HISTORY OF BIOLOGY (For Student,s)

The birth of biology: 5th - 4th century BC

The Greek philosophers, voracious in their curiosity, look with interest at the range of living creatures, from the humblest plant to man himself. A Greek name is coined by a German naturalist in the early 19th century for this study of all physical aspects of natural life - biology, frombios (life) andlogos (word or discourse). It is a subject with clear subdivisions, such as botany, zoology or anatomy. But all are concerned with living organisms.

The first man to make a significant contribution in biology is Alcmaeon, living inCrotona in the 5th century. Crotona is famous at the time for its Pythagorean scholars, but Alcmaeon seems not to have been of their school.


Alcmaeon is the first scientist known to have practised dissection in his researches. His aim is not anatomical, for his interest lies in trying to find the whereabouts of human intelligence. But in the course of his researches he makes the first scientific discoveries in the field of anatomy.

The subsequent Greek theory, subscribed to even byAristotle, is that the heart is the seat of intelligence. Alcmaeon reasons that since a blow to the head can affect the mind, in concussion, this must be where reason lies. In dissecting corpses to pursue this idea, he observes passages linking the brain with the eyes (the optic nerves) and the back of the mouth with the ears (Eustachian tubes).


Aristotle may be wrong about the brain being in the heart, but in general he gives a far more complete and well observed account of biology than any other Greek philosopher.

He inaugurates scientific zoology in his reliance on careful observation. He is particularly acute in his study of marine life, having much to say on the habits of fishes, the development of the octopus family, and the nature of whales, dolphins and porpoises. He is also a pioneer in attempting a system ofclassification. Observing an unbroken chain of gradual developments, as the life of plants shades into that of animals, he acknowledges the complexity of the subject and seems almost to glimpse the pattern of evolution.


Aristotle's notes on botany are lost, but many of his observations no doubt survive in the earliest known botanical text - nine booksOn the History of Plantswritten by Aristotle's favourite pupil,Theophrastus.

Writing in about 300 BC, Theophrastus attempts to classify plants, as well as describing their structure, habits and uses. His remarks are based on observations carried out in Greece, but he also includes information brought back from the newHellenisticempire in the Middle East, Persia and India, resulting from the conquests of Alexander the Great.


The influential errors of Galen: 2nd century AD

The newly appointed chief physician to the gladiators in Pergamum, in AD 158, is a native of the city. He is a Greek doctor by the name of Galen. The appointment gives him the opportunity to study wounds of all kinds. His knowledge of muscles enables him to warn his patients of the likely outcome of certain operations - a wise precaution recommended in Galen'sAdvice to doctors.

But it is Galen's dissection of apes and pigs which give him the detailed information for his medical tracts on the organs of the body. Nearly 100 of these tracts survive. They become the basis of Galen's great reputation in medieval medicine, unchallenged until the anatomical work ofVesalius.


Through his experiments Galen is able to overturn many long-held beliefs, such as the theory (first proposed by the Hippocratic school in about 400 BC, and maintained even by the physicians ofAlexandria) that the arteries contain air - carrying it to all parts of the body from the heart and the lungs. This belief is based originally on the arteries of dead animals, which appear to be empty.

Galen is able to demonstrate that living arteries contain blood. His error, which will become the established medical orthodoxy for centuries, is to assume that the blood goes back and forth from the heart in an ebb-and-flow motion. This theory holds sway in medical circles until the time of Harvey.


Science's siesta: 8th - 15th century

In the profoundly Christian centuries of the European Middle Ages the prevailing mood is not conducive to scientific enquiry. God knows best, and so He should - since He created everything. Where practical knowledge is required, there are ancient authorities whose conclusions are accepted without question -Ptolemy in the field of astronomy,Galen on matters anatomical.

A few untypical scholars show an interest in scientific research. The 13th-century Franciscan friar Roger Bacon is the most often quoted example, but his studies include alchemy and astrology as well as optics and astronomy. The practical scepticism required for science must await the Renaissance. 

Leonardo's anatomical drawings: 1489-1515

In about 1489 Leonardo da Vinci begins a series of anatomical drawings. For accuracy of observation they are far in advance of anything previously attempted. Over the next twenty-five years he dissects about thirty human corpses, many of them at a mortuary in Rome - until in 1515 the pope, Leo X, orders him to stop.

His drawings, amounting to some 750, include studies of bone structures, muscles, internal organs, the brain and even the position of the foetus in the womb. His studies of the heart suggest that he was on the verge of discovering the concept of thecirculation of the blood.


Illustrated books: 16th century

It is a coincidence of great value to biology, in which observation is of prime importance, that theRenaissancerevival of interest in science coincides with the invention of printing. As soon as books can be published withwoodcutillustrations set among printed text, naturalists have not only a large new readership but also the ability to show what they have so carefully observed.

The first to make serious use of this opportunity is a botanist, Otto Brunfels, whose three-volumeHerbarum vivae eicones (Living images of plants) is published in Strasbourg between 1530 and 1540.


Brunfels' pioneering example is soon improved upon by another German botanist, Leonhard Fuchs, whoseHistoria Stirpium(History of plants) is published in Basel in 1542. Fuchs introduces a new accuracy, in his depiction and his verbal description of the plants.

A French naturalist of this period provides a good example of theRenaissanceimpulse to match and perhaps even outdo the classical authors. In 1546 Pierre Belon sets off on a two-year tour of lands round the eastern Mediterranean with the specific purpose of finding and depicting animals and plants described by ancient writers.


Belon's travels and observations are recounted in a succession of illustrated volumes published in Paris during the 1550s - on fishes and dolphins (1551), on conifers (1553), on general Middle Eastern curiosities (1555), on birds (1555) and finally 'portraits of birds, animals, snakes, herbs, trees, men and women of Arabia and Egypt, together with a map of Mount Athos and of Mount Sinai for the better understanding of their religion' (1557).

Belon is an unashamed generalist. Meanwhile a highly specialized volume, the most significant of all the early illustrated scientific works, has been published in Basel in 1543 - bringing to a wide public the discoveries of Vesalius.



Vesalius and the science of anatomy: 1533-1543

A young medical student, born in Brussels and known to history as Vesalius, attends anatomy lectures in the university of Paris. The lecturer explains human anatomy, as revealed byGalen more than 1000 years earlier, while an assistant points to the equivalent details in a dissected corpse. Often the assistant cannot find the organ as described, but invariably the corpse rather than Galen is held to be in error.

Vesalius decides that he will dissect corpses himself and trust to the evidence of what he finds. His approach is highly controversial. But his evident skill leads to his appointment in 1537 as professor of surgery and anatomy at the university of Padua.


In 1540 Vesalius gives a public demonstration of the inaccuracies ofGalen's anatomical theories, which are still the orthodoxy of the medical profession.

Galen did many of his experiments on apes. Vesalius now has on display - for comparison - the skeletons of a human being and of an ape.


Vesalius is able to show that in many casesGalen's observations are indeed correct for the ape, but bear little relation to the man. Clearly what is needed is a new account of human anatomy.

Vesalius sets himself the task of providing it, illustrated in a series of dissections and drawings. He has at his disposal a method, relatively new in Europe, of ensuring accurate distribution of an image in printed form - the art of thewoodcut. His studies inaugurate the modern science of anatomy.
 
At Basel, in Switzerland, Vesalius publishes in 1543 his great work - De humani corporis fabrica (The Structure of the Human Body). There are seven volumes including numerous magnificentwoodcut illustrations. The book is an immediate success, though naturally it enrages the traditionalists who followGalen. Galen's theories have, after all, the clear merit of seniority. They are by now some 1400 years old.

But for those willing to look with clear eyes, the plates in Vesalius's volumes are a revelation. For the first time human beings can peer beneath their own skins, in these strikingly clear images of what lies hidden.

Attempts at classification: 1583-1704

It is a natural impulse for any academic, confronted by the bewildering array of nature's living forms, to try and establish some degree of order. One of the first to make a successful attempt is Andrea Cesalpino, whose De Plantis of 1583 classifies plants according to the characteristics of their flowers, seeds and fruits.

The Swiss physician and botanist Gaspard Bauhin extends Cesalpino's work in two books (Phytopinax1596, Pinax theatri botanici1623). Both titles mean 'gallery of plants', and Bauhin classifies some 6000 examples. The main significance of his work is that he is the first to arrange plants in separate groups, or genera.
 
Bauhin's work was the beginning of the binomial (two-name) system which subsequently prevailed in the classification of living organisms. Each is placed in a category, and the classification combines the name of the category with that of the wider group of which the organism is considered to be a member..

These two levels of classification eventually become standardized as the genus and the species. A basic problem of classification within this arrangement is to decide how much apparent variation can be allowed to plants or animals grouped as a single species. This is resolved in the work of the English naturalist John Ray, who makes extensive tours in Europe during the 1660s with his patron Francis Willughby. Their express purpose is to classify all plants and animals.


Ray publishes classifications of birds (1676), plants (from 1682), fishes (1686), land animals (1693) and insects (1705). In their original partnership the plan was for Willughby to undertake the animals and Ray the plants. Willughby dies young, in 1672, and Ray credits him with the text on birds and fishes (though amplifying it himself).

The greatest achievement is Ray's own work on botany. TheHistoria Plantarum(1686-1704) describes some 18,600 plants, categorizing them in ways which hold good today. His most influential decision is defining a species as a group which has a mutual fertility, each member capable of reproducing with any other. Ray's efforts prepare the way forLinnaeus.


Harvey and the circulation of the blood: 1628

A book is published in 1628 which provides one of the greatest breakthroughs in the understanding of the human body - indeed perhaps the greatest until the discovery of the structure of DNA in the 20th century.

The book consists of just fifty-two tightly argued pages. Its text is in Latin. Its title isExercitatio anatomica de motu cordis et sanguinis in animalibus ('The Anatomical Function of the Movement of the Heart and the Blood in Animals'). Its author is William Harvey. In this book he demonstrates beyond any reasonable doubt an entirely new concept. Blood, he shows, does not drift in the body in any sort of random ebb and flow. Instead it is pumped endlessly round a very precise circuit.



Until now it has been assumed that the blood in arteries and the blood in veins are different in kind. It is well known that they are of a different colour, and there have been many theories as to what each supply of blood does.

The most commonly held belief is that arterial blood carries some sort of energy connected with air to the body (not far from the truth), and that blood in the veins distributes food from the liver (less accurate).


By a long series of dissections (from dogs and pigs down to slugs and oysters), and by a process of logical argument, Harvey is able to prove that the body contains only a single supply of blood; and that the heart is a muscle pumping it round a circuit.

This circuit, as he can demonstrate, brings the blood up from the veins into the right ventricle of the heart; sends it from there through the lungs to the left ventricle of the heart; and then distributes it through the arteries back to the various regions of the body.


After much initial opposition, Harvey's argument eventually convinces most of his contemporaries. But there are two missing ingredients. His theory implies that there must be a network of tiny blood vessels bringing the blood from the arterial system to the venous system and completing the circuit. But his dissections are not adequate to demonstrate this. It is not till four years after his death that Marcello Malpighi observes the capillaries.

And Harvey is unable to explain why the heart should circulate the blood. That explanation will have to await the discovery ofoxygen.

Malpighi and the microscope: 1661

Marcello Malpighi, a lecturer in theoretical medicine at the university of Bologna, has been pioneering the use of themicroscope in biology.

One evening in 1661, on a hill near Bologna, he uses the setting sun as his light source, shining it into his lens through a thin prepared section of a frog's lung. In the enlarged image it is clear that the blood is all contained within little tubes.
 
Malpighi thus becomes the first scientist to observe the capillaries, the tiny blood vessels in which blood circulates through flesh . They are so fine, and so numerous, that each of our bodies contains more than 100,000 kilometres of these microscopic ducts.

With their discovery, the missing link in Harvey'scirculation of the blood has been found. For the capillaries are literally the link through which oxygen-rich blood from the arteries first delivers its energy to the cells of the body and then finds its way back to the veins to be returned to the heart.


Leeuwenhoek and the microscope: 1674-1683

Malpighi's pioneering work with themicroscope is taken further by the Dutch researcher Anton van Leeuwenhoek. Teaching himself to grind lenses to a very high degree of accuracy and clarity (some of them providing a magnification of 300x), he uses a simple microscope with a single lens - in effect a tiny and extremely powerful magnifying glass.

With instruments of this kind he is able to observe phenomena previously too small to be seen. In 1674 he is the first scientist to give an accurate description of red blood corpuscles. In 1677 he observes and depicts spermatozoa in the semen of a dog. In 1683 he provides a drawing of animalculae (or bacteria) seen in saliva and dental plaque.


His discoveries, published for the most part in the Philosophical Transactions of the Royal Society in London (though he himself lives in Delft), vividly suggest the excitement of being the first to wander with such enlarged vision among the minutiae of the animal kingdom.

His account of the common flea follows its development from egg to the practical perfection of its adult anatomy. His researches demonstrate for the first time that the tiniest living things have a life cycle and generative systems like any larger creature.

The Linnaean system: 1735-1758

The Swenish botanist Carl von Linné, or in the Latin version of his name Linnaeus, is an obsessive classifier. Outside his own field of natural history he tries his hand at organizing a system of minerals and even of diseases. But his fame derives from his having finally put in place, at the end of an experimental period lasting nearly two centuries, the method of classification in the plant and animal kingdoms which still prevails today.

In 1735 Linnaeus publishesSystema naturae(System of nature), in which he proposes a system capable of classifying all living things. It is based on the twin categories genus and species, pioneered byBauhin and developed by John Ray.


Linnaeus begins his task by defining the genera into which the species of plants will be divided (Genera plantarum1737). Next, over a much longer period, he assigns some 6000 species of plants to their appropriate genera (Species plantarum1753). He follows this with an updated edition of theGenera in 1754.

Linnaeus' criterion for grouping plants, by the number of their stamens and pistils, has proved misleading and has been revised. But his version of the Binomial systemsurvives intact, applying to animals as effectively as to plants. He proposes the use of genus and species to classify animals in the tenth edition of Systema naturae(1758), listing 4236 species as a preliminary contribution.







Cuvier and paleontology: 1812

William Smithin the late 18th century has used the evidence of fossils in rock strata for the advancement of geology. Georges Cuvier studies the fossils for their own sake, and in doing so founds the science of palaeontology.

His researches concentrate on the fossils of mammals and reptiles found in rocks in the Paris region, with special emphasis on extinct mammals of the tertiary period. His results are published in 1812 in the four volumes of Recherches sur les ossements fossiles des quadrupèdes(Researchs on the fossil bones of quadrupeds).


The discoveries revealed in this pioneering work provide the basis for subsequent theories of evolution, though they do not suggest that explanation to Cuvier himself. Confronted by the remains of extinct species, he concludes that the earth has gone through a series of cycles (which he calls 'revolutions'), corresponding to the observableGeological periods.

Each revolution, he believes, ends in some catastrophe of nature which destroys most of the existing fauna and flora. The survivors are joined by fresh species resulting from a new bout of creation. Subsequent researches by others, unearthing transitional fossils, give weight to the argument for a more gradual or evolutionary process.

HISTORY OF PHYSICS (For Student,s)

                                 History of Physics

The History of Physics is intertwined with the History of Astronomy.  In fact, Astronomy is a subject area belonging to the broader topic of Physics.  Astronomy is a subset of Physics.
Historically science has its roots in peoples' efforts to understand and explain the world and the universe around them of which they are a part.  While many observations were made about phenomena here on earth, the heavens were also observed.  People wanted to know what was going on and why.  Their interest was born of concern and fear as well as curiosity.  They wanted to feel some degree of control of their lives or at least be able to explain what was going on and why.
Our collective knowledge about our environment, the earth and the sky, came about slowly through observation and interpretation of those observations.  Knowledge was accumulated slowly in different societies and cultures.  Sometimes the knowledge found was lost and only rediscovered much later.  The history of western civilization from several thousand B. C. to the present is very much a story of discovery, disagreement, loss, and rediscovery.
Early history of man involves very little ability to investigate more than could be observed with the senses.  This resulted in people making up stories to explain phenomena for which they had no real understanding.  This is not unlike stories made up to help little children deal with their every day experiences.  Often adults won't try explain the physics principles behind a thunder storm to a frightened little child, even if they understood it themselves.  Instead they make up a cute story to provide the child with something to explain a scary situation in terms of something less scary.  As an example, in many Christian homes in western civilization the explanation often given to little children afraid of thunder storms was that the angels were bowling.  The noise of the thunder was the noise of the bowling balls and the lightning was their using light to find the ball so they wouldn't lose it.
This explanation has nothing to do with what is going on in a thunder storm or what lightning or thunder is.  On the other hand it gives the child comforting information, which they can then use to face the world.  This same phenomenon can be seen in ancient civilizations.  People attributed phenomena to the presence or actions of gods.  A close look at ancient civilizations like the Greeks reveals a colorful history filled with such stories about gods.  All civilizations have their beliefs and mythologies (creation stories) explaining their origins and how the earth and sky came about.
On the other hand, among the people of these civilizations there were some who wanted to know more.  They didn't accept the myths on faith, but chose to investigate further.  These people wanted to find the truth so they could understand the world and the universe better. We find such people among the members of many societies of which we have knowledge.  Collectively, today, we might call such people scientists, though in their own times they may not have had that label.
"Historians have a tendency always to go further back.  They justify this because of the belief that one cannot understand what happens at a certain time without understanding the past."  (Daniel Barret - from his lecture notes, 1995.)
The study of mathematics and the sciences, particularly astronomy and physics, often begins with the Ancient Greeks.  There were other civilizations which predate or coexisted around the eastern Mediterranean that had certain knowledge of these subjects, but in a short review of events such as this page, only some of the most significant people and events are mentioned.  The most famous of the Greek philosophers Socrates, Plato, and Aristotle are often quoted or paraphrased, because it is these three that are seen as having a most significant impact on the development of western civilization.  What is a curious question is "What influence did other civilizations and their knowledge, such as the Egyptians, have on forming the thinking of these great philosophers and Greek knowledge and society as a whole?"  We'll leave that for you, the reader, to pursue, if you are curious.  We'll begin with the Greeks and the view that came down from Aristotle.  His influence was so great that it had a major impact on western civilization's philosophy, law, religion (Christianity), and science, all the way to the present.
The ancients' view was that the earth was the center of the universe.  Until the beginning of the renaissance only a few in western civilization ever thought that the sun might be the center of planetary motion.  It was never a popular view, though, because Aristotle's explanation of phenomena both on earth and in the heavens dominated western thinking until the renaissance. They were aware of five known planets and believed that they moved in complicated paths.  The need to explain their motion in terms of complicated paths was the result of the apparent complicated motions of planets as they are observed moving across the sky.  This observed motion is called apparent motion, which means the motion as seen by an observer here on earth.  The planets do not appear to move at a steady rate across the sky from night to night, as one who does not watch the sky might think.  In fact there are times when a planet like Mars appears to move backwards with respect to its usual forward motion.  This motion is called retrograde motion and required some very creative imaginations to explain this motion based on a belief that the earth was the center of everything.
Aristotle viewed the process of learning as one of observation and thinking.  He would study the ideal situation, but he would not conduct experimentation.  He believed that truth could be found through good reasoning powers and experimentation would not enhance any study of the world.   Experimentation was not something he supported in his ideas about how to determine the answers to questions.  The insinuation of doubt and suspicion of the scientific method (the use of experimentation as well as observation) even in today's society no doubt has its roots in Aristotelian logic, though some people are less skilled in logical reasoning than others and may feel intimidated by the scientific method, because they do not really understand it for the process that it is.  It wasn't until the beginning of the renaissance that we see a change in the direction of thought as experimentation and observation become equally important.  Galileo Galilei in the 14th gave us two very important tools that brought about change in the way the earth and sky were studied and conclusions made.  He believed in experimentation, including the theoretical experiment which he, himself, used to investigate falling bodies. He also used mathematics to describe and define phenomena, something which hadn't really been done before.
Socrates (470-399 B.C.) He is a famous Greek philosopher whose ideas are the basis for western civilization's philosophy.  He is also well known for his teaching style which is based on a dialogue where the teacher and pupil both reason through an argument to the truth.  This is known today as the Socratic method.
Plato (427-347 B.C.) He is a student of Socrates. His philosophy is a belief in an idealized world.  He saw the real world as decaying and changing.  He believed that true knowledge could not be found from such a corruptible world.  Plato outlined the creation of the world as the actions of a demiurge (a supernatural being) working with less than perfect material creating the world according to a rational plan.  This being fashioned the world as perfect as possible within the limitations of what it had to work with.  This perfection involved using the circle, which he considered the most perfect shape, to describe the motion of the heavenly bodies.
Eudoxus of Cynidus (400-347 B.C.)  He was an associate of Plato.  He created a very complex astronomy in terms of his description of the movement of heavenly bodies.  He described the motion by means of concentric spheres.  For example the moon was explained by three concentric spheres.  The outer most sphere moved it from east to west every 24 hours.  The second sphere moves the moon through one complete revolution every 223 synodic months.  The third sphere accounts for the moon's motion through the zodiac.  The system becomes more and more complex as other heavenly bodies' motions are described in terms of concentric spheres.  [These types of mental imaginings come close to describing a possible explanation for the apparent motion of objects in the sky.  They do not, unfortunately have any connection to the truth, that is, what is really going on as we observe the motion of objects in the sky.]
Aristotle (384-322 B.C.) He was a student of Plato.  He saw the sphere as the perfect shape.  He adopted the ideas of Eudoxus about concentric spheres.  He even went further and said that the system described by Eudoxus involves physically real spheres.  He related this idea to the model he had created for the physical world of which he said the following.
Celestial Objects above the moon were part of a fifth, perfect element called the aether. From the moon on down everything was made of the four elements consisting of earth, fire, water, and air. These elements had their particular motions that was their nature to move in.  These are listed below.

• Fire moves up
• Air moves up
• Water moves down
• Earth moves down

The center of the earth (the center of the universe) was where all things that moved down moved towards.  The earth was spherical because of all of the things that moved downwards towards its center.  Which ever element dominated an object's make up (composition in terms of the four elements) determined which way an object would move.  The heavens were considered perfect, such that anything made up of aetheral matter moved in a circle that was above and distinct from the earth.
Ptolemy (90-168 A.D.)  He defined a very complex movement of heavenly bodies that complimented Aristotle's physics that said matter must move either up, down, or in a circle according to its nature.  He added more spheres to an already complicated system.  His model was more accurate than that of Eudoxus.  In fact though his model was not based upon what was really happening in terms of the movement of the planets, it did as good a job as a tool for making predictions as to apparent motion in the sky as the early renaissance "astronomers" could operating with newly rediscovered information.  [This means that as a "calculating machine" of sorts, his model was useful for predicting positions of objects in the sky, but did not in any way explain the actual motions of the planets and moons in our solar system or why they moved as they did.]
It can be said at this point that the goal of explaining apparent motion of the planets etc. involved a way of thinking that focused on preserving the appearances, that which was seen, and not on the truth based on experiment and observation that would focus on what events were occurring to produce the appearances or what was seen.  It should be noted here that there was a small group of Greeks called the Ionians who interpreted what they saw in the heavens as the sun being at the center of the universe.  Their ideas were not held by the general population or the more influential people such as Aristotle.  Their ideas would go unnoticed for close to 2,000 years until the heliocentric universe was "rediscovered".
Copernicus (1473-1543 A.D.)  In 1543 year his heliocentric theory was published.  His model said that the sun was at the center of things and not the earth.  He said that the five known planets as well as the earth were all traveling around the sun, making sun the center of all of the action.
At the time, the known planets from the sun outwards were:

1. 1 Mercury
2. 2 Venus
3. 3 Earth
4. 4 Mars
5. 5 Jupiter
6. 6 Saturn

While he did make a serious bold step in the scheme of things, producing a theory of heliocentricity, he did not abandon the use of epicycles.  An epicycle is a small circular path whose center moved along the circumference of a larger circle whose center was the earth.  He kept the idea of epicycles because he believed that the paths of the planets were circles and the only model that would explain the motion seen in the sky using circles requires that the planets follow epicycles rather than single circles around the earth.  [It was not yet learned that the true shape of the planetary orbits were ellipses and epicycles were not in anyway a true description of how planets moved about the sun.]
Tycho Brahe (1546-1601 A.D.)  He was man who at a young age had a strong interest in astronomy and some connections at court.  He was upset that current astronomical tables of information were noticeably off in their measurements.  The Danish King, Fredrick II, gave him the small island of Hven off of the coast of Denmark.  He erected an observatory (some sources say two were erected) on this island.  Along with the help of assistants, but without the use of telescopes (they were not invented yet), he carried out the most exact astronomical observations ever done up to that point in time.  He used a great mural quadrant, a device that works similar to a giant protractor, to determine the height above the horizon of objects at the time they cross the meridian.  In 1577 he witnessed a comet which because of his accuracy showed it to be six times further from earth than the moon.  This didn't bode well for the popular Aristotelian model of the universe which said that the heavens were unchanging.  It also was bad for the solid sphere model because the comets path took it right through those spheres.  Before this time, comets were just thought of as being "shooting stars" moving above the earth but closer to the earth's surface than the moon.  He looked for stellar parallax which would indicate that the earth is moving, but with the unaided eye he could not detect any.  Thus caused him to doubt the earth moved and disagreed with Copernicus.  For over twenty years he did gather volumes of data, data which would eventually fall into the hands of Johannes Kepler.  Tycho himself believed that Saturn, Jupiter, and Mars revolve counter clockwise around the sun.  Mercury and Venus did too, but on smaller circles.  The sun revolves about the earth once a day while the sphere carrying the stars turns once a day as well.  Tycho supported an earth centered universe.
Johannes Kepler (1571-1630)  Kepler asked question like "why were there six planets?" and "why do those further from the sun move more slowly?"  Kepler studied and taught astronomy.  While teaching he came to the conclusion that Copernicus was correct, but there was no need for epicycles.  Instead he reasoned that the ratios of the planetary orbital radii were related to certain geometric shapes.  He first noted that the ratio of Jupiter's to Saturn's radii was similar to a ratio of an inner circle to an outer circle with a triangle inscribed within it, except that actual geometric shapes that appear to work for the ratio of planetary orbits are more complex. He set out and determined the geometric shapes which would fit inside an inner - outer circle ratio of each pair of planetary radii.  Below is a list of the geometric shapes that he determined would fit between the circles representing the orbits of the six known planets.
Mercury
            > octahedron
Venus
            > icosahedron
Earth
            > dodecahedron
Mars
            > tetrahedron
Jupiter
            > cube
Saturn
He communicated this information both to Tycho Brahe and Galileo Galilei.  He was convinced that this geometric pattern explained why only six planets existed and why they had the orbital radii that they did.  Later he joined Tycho Brahe.  Kepler acquired Tycho Brahe's data when Tycho died in 1601.  Kepler studied this data for a good twenty years.  It was during this time that he developed his three laws of planetary motion.  These three laws are:
1. The planets travel in elliptical paths.  (Their orbits are ellipses with the sun at one of the two foci)
2. The planets sweep out equal amounts of area in equal amounts of time.  This law says that a planet such as the earth speeds up and slows down during one revolution about the sun.  Since the sun is off center, being at one of the two focus points of the elliptical path it slows down as it moves away from the sun and speeds up as it moves closer to the sun.
3. The relationship between the period (the time for one revolution about the sun) and the average radius of a planet is related by the mathematical expression that says the period squared divided by the average radius cubed is equal to a numerical constant.  If a person knows that constant it is easy to calculate the radius of an orbit from the period of the planet or the period of the planet from the average radius of the an orbit.
Galileo Galilei (1564-1642)  Galileo was a brilliant man.  He gave us the idea of doing thought experiments as well as reinforced the concept of doing physical experiments.  He also gave us the idea of using mathematics to describe relationships among variables and describe phenomena.
A very big investigation on his part was the concept of motion.  Aristotle, who used as his approach observation followed by logical thought to arrive at "truths", reasoned that the natural state of an object was at rest because he saw all moving objects slow down and come to rest.  He either didn't perceive or couldn't conceive of the reason an object slowed down. He apparently was not aware of the presence of the force we call friction.  Slowing down to him was a natural state of things.  He wasn't aware of forces at work.  Galileo, on the other hand, believed that a person should test ideas with observations based upon further experimentation wherever possible and see whether the results could still be explained in terms of existing theories.  Theories have to be continually tested as new data through new experimentation is gathered and analyzed.  Galileo reasoned that the natural state of an object is either at rest or moving with constant speed, for as long as no unbalanced forces are acting on the object.  Aristotle didn't realize that on earth objects always tend to come to rest because of the unbalanced force of friction acting on the object.  Galileo understood that an object at rest would continue to remain at rest until an unbalanced force acted on it.  Galileo was also able to reason that if friction and other forces acting on an object were balanced (canceled out, if you prefer), an object not at rest would continue to move along with constant speed because there would be no reason for it to ever come to rest or even change its speed until an unbalanced force acted on it.
Aristotle also reasoned that heavier objects fall faster than lighter ones although today we know that that only appears to happen whenever friction is present, because friction has a greater effect on small light weight objects than on large heavy objects.  Galileo reasoned that all objects fall at the same rate when there are no unbalanced forces like friction acting on them.  He wasn't able to create an environment where he could reduce friction to essentially zero such as we do today in vacuum chambers, but he was able to imagine it and work through a thought experiment that led to his correct conclusion.  Galileo studied the motion of objects under the influence of the force of gravity and came to understand the concept of acceleration.
Galileo also heard about the development of the telescope by the Flemish optician Hans Lipperhey.  In 1609 he made one of his own.  Though he didn't invent the telescope, he did make significant improvements to it.  He ground his own lenses and had eight to nine power telescopes when others had only six power telescopes back in 1609.  At the end of 1610 he had a twenty power scope.  By today's standards these is not impressive at all, but at the beginning of this technology this was great stuff.  Galileo studied the surface of the moon making some sketches of what he saw.  He studied the four large moons of Jupiter.  He found stars that were not visible with the naked eye.  He found that unlike planets and moons which appeared larger and with more detail when observed through more powerful telescopes, stars did not appear to look larger, but did appear as brighter points of light.  He published the "Starry Messenger" in which he reported his findings.
Galileo did not make known his support of Copernicus' heliocentric model until 1613.  The discovery of the four moons of Jupiter appears to be the piece of the puzzle that really convinced him of the heliocentric view of the heavens as being correct.  He dismissed the geocentric (earth centered) view.  Of course this got him into trouble with the Roman Catholic Church which had dominated western civilization since the time of the Roman empire.  The church had secured and preserved thousands and thousands of documents not just in the Vatican, but in many monasteries scattered across western Europe, etc., even as far away as Ireland.  Along with the Renaissance came the reformation and the Church was being attacked by a number of groups who were trying to change Christianity and/or abolish it altogether.  They were very skeptical of Galileo's ideas because they ran contrary to what had been believed true about the universe for some 2,000 years.  Their cautiousness is understandable from the point of view of that they had preserved western civilization and the faith from the time of the fall of the roman empire, through the dark ages, to the beginning of the renaissance, when Galileo came out with his research results.  Its a complicated story, but in the end he was placed under house arrest on a nice estate with maid service because he couldn't prove beyond a doubt that his evidence was proof positive of a heliocentric universe.  He continued to write and had material snuck out to Holland for publishing.
Isaac Newton (1642-1727)  Newton was born into a poor farming family.  His interest lay elsewhere and he went to Cambridge to become a preacher.  It was here that he studied mathematics and got into considering planetary orbits and the related physics of motion.  Newton developed his famous three laws of motion which were defined and described in his large publication the "Philosophiae Naturalis Principia Mathematica" (Mathematical Principles of Natural Philosophy) (1687), often shortened to Principia Mathematica or simply "the Principia.''
The story about his developing these three laws of motion says that he did it when he left the university to return to the farm so as to avoid the plague.  Here is where the story of the falling apple comes from.  While we won't really ever know whether he was actually struck by an apple, we do know that what got him thinking about gravity were questions such as "If an apple and the moon are both affected by gravity, then why does only the apple fall to earth and not the moon?".  He took and built upon Galileo's thinking about forces and motion and investigated the concept of force much further developing his three laws of motion. In addition to his three laws of motion he developed the equation linking the force of gravity to both the mass of the two objects between which there was a force of attraction and the distance which separated them.  This is referred to as Newton's Law of Universal Gravitation.  His investigation of motion lead him to develop Calculus from the point of the derivative.  A German scientist by the name of Leibniz (1646-1716 A.D.) also developed Calculus from the point of view of the integral.
Newton's Three Laws of Motion:
1. Newton's First Law:  An object that is at rest will remain at rest and an object that is moving in a straight line with constant velocity will continue to do so, if the net force (the sum of all forces acting on the object) is equal to zero.  Newton generalized Galileo's study of motion to fit motion in any direction.  His first law is often referred to as the law of inertia.  Inertia is the tendency of an object to resist change, as in this case, a change in its motion.
2. Newton's Second Law:  The force exerted on an object is a function of both the object's mass and the rate of acceleration it experiences as a result of the force.  This means that force is both proportional to mass and to acceleration when one of the two remains constant, but mass and acceleration are inversely proportional to one another when force remains constant.
The equation for Newton's Second Law
F = m a F is Force, m is mass, and a is acceleration.
3. Newton's Third Law:  Whenever one object exerts a force on a second object, the second object exerts a force on the first object.  Sometimes this law is described as saying "to every action there is an equal and opposite reaction".  It must always be remembered that the action and the reaction force are acting on different objects.  As you think about this look at your hand when you are pushing against a heavy object.  That the shape of your hand is affected is evidence that a force is acting on it and it is not just exerting a force on something else.  You can feel the force as well and if you are pushing hard enough, it is pushing back on you hard enough to make your hand hurt.  An ice skater could move across the ice by pushing against something, and the something will push back on the skater.  For example, a stationary skater in the middle of a low friction smooth frozen pond holding a handful of baseballs could move off the ice by throwing one ball at a time until they have reached the edge of the pond The as the each ball is thrown (pushed) forward with a force it pushes backwards with an equal but opposite force.  This too is how rocket engines work the hot exhaust gas is pushed out the rear of the engine while at the same time the hot gas is pushing the back on the rocket.  As a final example, consider when you walk or drive a car.  You or the car tire are pushed forward by the earth at the same time your foot or the car (tire) is pushing back on the earth.
Newton's Law of Universal Gravitation:  Newton was able to express his law in terms that applied to the motion of planets orbiting the sun.  His law agreed with Kepler's third law which provided proof that he had he and Kepler were on the right track and in agreement about the observable known universe.  His law defined the force of gravity in terms of the mass of the two objects exerting gravitational force on each other and the distance which separates them.  His law says that the Force of gravity between two objects varies directly with the masses of the two objects and varies inversely with the distance separating them squared.
The Equation for Newton's Law of Universal Gravitation
F_g a m₁ m₂ / d².     (a proportionality)
F_g = G m₁ m₂ / d².          (an equality) Where G is a numerical constant changing the proportionality into an equality.  Unfortunately Newton did not have the means (the equipment) to measure very small gravitational forces in a laboratory experimental setting so he wasn't able to determine the value for G.  It wasn't until around 100 years later that a person by the name of Henry Cavendish was able to experimentally determine the value for G and calculations using Newton's Law of Universal Gravitation could be done.
Modern Physics (The 20th century, 1900-2000)  The physics coming down to us from the past which focusses very much on motion and the nature of the universe was further defined and perfected by Isaac Newton was dominant until the beginning of the 20th century.  This physics is sometimes called Newtonian physics or more often  generally referred to as classical physics.  This physics is adequate for most everyday phenomena involving motion where relatively large massive objects moving with relatively slow velocities are involved.
By the early 1900's though a very famous person by the name of Albert Einstein came along and shook up the world by saying the universe is not a big mechanical gadget like a lot of people who understood newton were saying.  Instead it is a much more complicated and at the same time curiously interesting and different than what Newton's view gave us.  The universe is very different when you consider that small high speed particles do not behave as would be predicted using Newton's Laws.  Instead they behave according to a new set of principles that require one to open one's mind to exciting new principles and century of research into the unknown of the very large and the very small.  Einstein kicked off the 20th century with his theory of relativity and we left the last century with emphasis on quantum theory.
This is as far as this summary goes for now.  Understand that the information provided here is just the proverbial first step into the 1,000 mile journey.  If you choose to take it, you'll enjoy it.

History of Chemistry (For Students)

Chemistry is a branch of science that has been around for a long time. In fact, chemistry is known to date back to as far as the prehistoric times. Due to the amount of time chemistry takes up on the timeline, the science is split into four general chronological categories. The four categories are: prehistoric times - beginning of the Christian era (black magic), beginning of the Christian era - end of 17th century (alchemy), end of 17th century - mid 19th century (traditional chemistry) and mid 19th century - present (modern chemistry).

Time Intervals	Specific Times	Events	Description
Prehistoric Times -Beginning of the Christian Era (Black Magic) http://tqd.advanced.org/2690/hist/black.html	1700 BC	King Hammurabi's reign over Babylon	Known metals were recorded and listed in conjunction with heavenly bodies.
	430 BC	Democritus of ancient Greece	Democritus proclaims the atom to be the simplest unit of matter. All matter was composed of atoms.
	300 BC	Aristotle of ancient Greece	Aristotle declares the existence of only four elements: fire, air, water and earth. All matter is made up of these four elements and matter had four properties: hot, cold, dry and wet.
Beginning of the Christian Era -End of 17th Century (Alchemy) http://tqd.advanced.org/2690/hist/alchemy.html	300 BC - 300 AD	The Advent of the Alchemists	Influenced greatly by Aristotle's ideas, alchemists attempted to transmute cheap metals to gold. The substance used for this conversion was called the Philosopher's Stone.
	13th Century (1200's) - 15th Century (1400's)	Failure of the GoldBusiness	Although Pope John XXII issued an edict against gold-making, the gold business continued. Despite the alchemists' efforts, transmutation of cheap metals to gold never happened within this time period.
	1520	Elixir of Life	Alchemists not only wanted to convert metals to gold, but they also wanted to find a chemical concoction that would enable people to live longer and cure all ailments. This elixir of life never happened either.
	End of 17th Century	Death of Alchemy	The disproving of Aristotle's four-elements theory and the publishing of the book, The Skeptical Chemist (by Robert Boyle), combined to destroy this early form of chemistry.
End of 17th Century - Mid 19th Century (Traditional Chemistry) http://tqd.advanced.org/2690/hist/traditional.html	1700's	Phlogiston TheoryCoulomb's Law	Johann J. Beecher believed in a substance called phlogiston. When a substance is burned, phlogiston was supposedly added from the air to the flame of the burning object. In some substances, a product is produced. For example, calx of mercury plus phlogiston gives the product of mercury. Charles Coulomb discovered that given two particles separated by a certain distance, the force of attraction or repulsion is directly proportional to the product of the two charges and is inversely proportional to the distance between the two charges.
	1774-1794	Disproving of the Phlogiston Theory	Joseph Priestley heated calx of mercury, collected the colorless gas and burned different substances in this colorless gas. Priestley called the gas "dephlogisticated air", but it was actually oxygen. It wasAntoine Lavoisier who disproved the Phlogiston Theory. He renamed the "dephlogisticated air" oxygen when he realized that the oxygen was the part of air that combines with substances as they burn. Because of Lavoisier's work, Lavoisier is now called the "Father of Modern Chemistry".
	1803	Dalton's Atomic Theory	John Dalton publishes his Atomic Theory which states that all matter is composed of atoms, which are small and indivisible.
Mid 19th Century - Present (Modern Chemistry or 20th Century Chemistry) http://tqd.advanced.org/2690/hist/modern.html	1854	Vacuum Tube	Heinrich Geissler creates the first vacuum tube.
	1879	Cathode Rays	William Crookes made headway in modern atomic theory when he used the vacuum tube made by Heinrich Geissler to discover cathode rays. Crookes created a glass vacuum tube which had a zinc sulfide coating on the inside of one end, a metal cathode imbedded in the other end and a metal anode in the shape of a cross in the middle of the tube. When electricity was run through the apparatus, an image of the cross appeared and the zinc sulfideglowed. Crookes hypothesized that there must have been rays coming from the cathode which caused the zinc sulfide to fluoresce and the cross to create a shadow and these rays were called cathode rays.
	1885	The Proton	Eugene Goldstein discovered positive particles by using a tube filled with hydrogen gas (this tube was similar to Thomson's tube...see 1897). The positive particle had a charge equal and opposite to the electron. It also had a mass of 1.66E-24 grams or one atomic mass unit. The positive particle was named the proton.
	1895	X-rays	Wilhelm Roentgen accidentally discovered x-rays while researching the glow produced by cathode rays. Roentgen performed his research on cathode rays within a dark room and during his research, he noticed that a bottle of barium platinocyanide was glowing on a shelf. He discovered that the rays that were causing the fluorescence could also pass through glass, cardboard and walls. The rays were called x-rays.
	1896	Pitchblend	Henri Becquerel was studying the fluorescence of pitchblend when he discovered a property of the pitchblend compound. Pitchblendgave a fluorescent light with or without the aid of sunlight.
	1897	The Electron and Its PropertiesRadioactive Elements	J.J. Thomson placed the Crookes' tube within a magnetic field. He found that the cathode rays were negatively charged and that each charge had a mass ratio of 1.759E8 coulombs per gram. He concluded that all atoms have this negative charge (through more experiments) and he renamed the cathode rays electrons. His model of the atom showed a sphere of positively charged material with negative electrons stuck in it. Thomson received the 1906 Nobel Prize in physics. Marie Curie discovered uranium and thorium within pitchblend. She then continued to discover two previously unknown elements: radium and polonium. These two new elements were also found in pitchblend. She received two nobel prizes for her discovery; one was in chemistry while the other was in physics.
	1909	Mass of the Electron	Robert Millikan discovered the mass of an electron by introducing charged oil droplets into an electrically charged field. The charge of the electron was found to be 1.602E-19 coulombs. Using Thomson's mass ration, Millikan found the mass of one electron to be 9.11E-28 grams. Millikan received the 1932 Nobel Prize in Physics for this discovery.
	1911	Three Types of Radioactivity	Ernest Rutherford sent a radioactive source through a magnetic field. Some of the radioactivity was deflected to the positive plate; some of it was deflected to the negative plate; and the rest went through the magnetic field without deflection. Thus, there were three types of radioactivity: alpha particles (+), beta particles (-) andgamma rays (neutral). By performing other experiments and using this information, Rutherford created an atomic model different from Thomson's. Rutherford believed that the atom was mostly empty space. It contains an extremely tiny, dense positively charged nucleus (full of protons) and the nucleus is surrounded by electrons traveling at extremely high speeds. The Thomson model was thrown out after the introduction of the Rutherford model.
	1914	Protons within a Nucleus	Henry Moseley attempts to use x-rays to determine the number of protons in the nucleus of each atom. He was unsuccessful because the neutron had not been discovered yet.
	1932	The NeutronNeutron Bombardment and Nuclear Fission	James Chadwick discovers the neutron. Enrico Fermi bombards elements with neutrons and produces elements of the next highest atomic number. Nuclear fissionoccurred when Fermi bombarded uranium with neutrons. He received the 1938 Nobel Prize in physics.
	1934	Artificial Radioactive Elements	Irene Curie and Frederic Joliot-Curie discovered that radioactive elements could be created artificially in the lab with the bombardment of alpha particles on certain elements. They were given the 1935 Nobel Prize.
	1940's	Manhattan Project	Albert Einstein and Enrico Fermi both warned the United States about Germany's extensive research on atomic fission reaction. Below the football field at the University of Chicago, the United States developed the very first working nuclear fission reactor. The Manhattan Project was in process.

 

Each link for each time interval contains some information about that period. Unfortunately, the information is sparse and the presentation of the info leaves much to be desired. However, more information on chemical history can be found in the links listed below. The list is collated in a chronological manner so like the table above, alchemy and black magic should be on top while traditional and modern chemistry should be closer to the end of the list. Also, there are some other links besides the ones that are in the time-interval section and these links should lead you to more information about the underlined topics.