Download Ethan Kessinger and Amanda Brockbank

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Amanda Brockbank and Ethan Kessinger
Physics, Period 5
Exploration 1: Ancient Physics
Any study of Ancient Physics must begin with the Babylonians. In fact, our entire
modern world would look completely different if it were not for the Babylonians. They created
the first written language, which started a pattern of ideas being
recorded and allowed ideas to pass on to others when they were
gone its original form. Ideas were passed along before, but the
accuracy was dependent on the person trusted with the
information. If people forgot or died before they were able to
explain their inventions/discoveries, then it was lost forever.
The Babylonians also had a very accurate counting system. In
trade as well as in science, the Babylonians had a system that
was consistent throughout the society. This was a very
important precursor to physics.
Aristotle had very specific ideas on the physical world.
His theories were taken as fact for centuries. The problem with
Figure 1 shows the Babylonian
language. This stone has survived
the tests of time and is a great
example of how permanent
written word was.
this was that Aristotle did not use tests and experiments to come
up with his ideas; Aristotle matched his ideas of the physical world with his philosophy.
Aristotle started out with preconceived notions, and found evidence and models that would
support those notions. Universities taught Aristotle physics for so many years, which hindered
these people from exploring the depths of physics. When a person is taught that something is
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true, they will not question the validity of the hypothesis nor will they look for other
explanations.
According to Aristotle, our planet was made up of four elements: Earth, Fire, Air, and
Water. Everything, living and nonliving, was made up of a combination of these elements. A
human for example was made up of all four elements. The Air made up the human’s lungs and
also served as its “breath of life.” The Fire kept the human warm (which is Aristotle’s way of
saying a human’s homeostasis). The Water made the humans blood. Finally, the Earth made the
human strong and also contributed to the human’s weight. In order to explain how water became
blood, Aristotle proposed that the concentrations of each element made the human look and
function the way that it did.
In Aristotle’s mind, all four elements were pure. However, our Earth and the air that we
breathe are not pure. They are mostly Earth and mostly Air,
but there are small concentrations of other elements.
Aristotle actually thought that there were five elements.
There were the four elements on our planet, and there was
one element that made up outer space. Quintessence, outer
spaces element, made up asteroids, starts, and all other space
matter.
Archimedes was also a Greek physicist, but he viewed
Figure 2 is a Roman copy of a bronze
Greek sculpture of Aristotle made during
his lifetime. Since the ancient artist was
carving 3-dimensionally instead of trying
to capture 3 dimensions on canvas, the
Greek sculpture would have been a much
more accurate depiction of Aristotle than
paintings of him. Bronze also holds up a
lot better than canvas, so even though all
we have today is a replica of the statue,
we can assume it is very accurate.
physics in a very different way than Aristotle did. While
Aristotle used philosophy and separated nature with
mathematics, Archimedes combined the two. He is viewed
by most as the first mathematical physicist. The other
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difference between Aristotle and Archimedes is that Archimedes used his knowledge to make
practical inventions. His most prolific invention was water screw. This was used in his time,
and is still used in some 3rd World countries, to move water from low-lying areas to ditches for
irrigation. This was a very important invention because of its simplicity. Archimedes used his
knowledge of motion to create a device that moved water out of “A double or triple helix built
from wood strips around a heavy wooden pole.” Archimedes is also said to have invented a
mirror that when directed at the sun shot a blast of fire in a specified direction. However, most
modern historians view this as a myth.
Even if his burning mirror did not exist, Archimedes did make several instruments of
war. He also discovered the physical law of buoyancy, known today as the Archimedes
principle. Archimedes’ principle states that “any body completely or partially submerged in a
fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force the magnitude of which
is equal to the weight of the fluid displaced by the body.” This is the first time that scientists
were able to explain the phenomenon of buoyancy and how it was the inverse of gravity.
Because of this, Archimedes is a very influential physicist whose ideas and research continue to
be used.
In the field of astronomy, Ptolemy was by far the most influential person of this time. He
did many things in his lifetime, and was a noted mathematician and geographer. However, his
astronomical contributions, such as codifying the Greek geocentric view of the universe, and
rationalizing his generations ideas on the apparent motions of the planets. Claudius Ptolemaeus,
now universally recognized as Ptolemy, lived in Alexandria around 87 AD to around 150 AD.
While he authored several scientific treaties, his most remembered work was The Algamist. In
this, he focused on many different things. He challenged Aristotle’s cosmological outline,
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determined latitude lines, followed the motion of the sun, and looked at eclipses. The level of his
research and hypothesis are incomprehensible when you look at the lack of information available
at this time for him to build off of.
In 13 books, Ptolemy’s The Algamist used kinematic to explain solar, lunar, and
planetary motion. This book gave all scientists a much clearer picture of the physical world.
Islamic scientists especially used Ptolemy’s information effectively, and this led to their vast
contribution to physics. Islamic scientists are often famous for their contributions to the
mathematic world, such as the discovery of the number zero, and the coining of the term
algebra. However, there were three scientists who also made large contributions to the study of
the physical world; scientists whose discoveries paved the way for physicists such as Newton
and Bacon.
The first of these scientists was named Abu Raihan al-Biruni. Though he studied a wide
range of topics in his life, some of his most significant findings were the very beginnings of what
we now know as gravity. He defined the concept of gravitation as “the attraction of all things
towards the center of the earth.” Given the fact that al-Biruni lived from 973 to 1048, this
definition is impressively close to the modern definition, which is, “the force of attraction
between any two masses.” Though the concept of specific gravity is present in Archimedes work,
Al-Biruni was the first to define it. He was also one of the first to apply the concept of specific
gravity to an experiment: after measuring the specific gravity and the volume of gemstones, alBiruni found a direct correlation between the two measurements. Up until that point, the general
belief about gravity in relation to astronomy and planets was that which Aristotle had
hypothesized centuries earlier: heavenly bodies do not have gravity. Al-Biruni challenged this
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concept, saying that if gravitation, previously defined by him, pulls everything towards the
center, and then there must be gravity between the planets in order to keep them from falling
towards that center. While this is not fully correct, he was still one of the first physicists to think
critically about gravity and its application in the universe.
Al-Biruni made important discoveries and observations about other aspects of the
physical world that would come to be important in future scientist’s work. He was the first to
notice that the speed of light is far greater than the speed of sound and was the first to realize
acceleration is connected to non-uniform motion, which is a part of Newton’s second law. He
also was the first to observe that movement and friction cause heat. Applying this to the world,
he hypothesized that a lack of movement explains why it is so cold near the geographic poles.
The earth and the water form one globe, surrounded on all sides by air. Then, since much
of the air is in contact with the sphere of the moon, it becomes heated in consequence of
the movement and friction of the parts in contact. Thus there is produced fire, which
surrounds the air, less in amount in the proximity of the poles owing to the slackening of
the movement there.
Again, not all of his concepts about physics were completely correct. However, early physicists
like al-Biruni were more important because they were hypothesizing and providing a stepping
stone for future scientists to build upon.
Following al-Biruni came Abu'l Fath' Abd al-Rahman al-Khazini, who also played a
major role, among other things, in furthering the work on gravity. Of his three major works, two
are on astronomy. The first, al-Zidj al mu`tabar al-sandjari al-sultani (Sinjaric Tables), gave the
positions of 46 stars, calculated from the data given in the Almagest and gave a description of a
24 hour water clock he had built for astronomical purposes. This is one of the earliest recorded
examples of an astronomical clock. His second book, Risala fi ‘l-alat (Treatise on Instruments),
was a seven part book describing different astronomical instruments. However, his most
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influential book was called Kitab Muzan al-hikma (The Book of the Balance of Wisdom), which
was on hydrostatics and gravity. Using what had previously been published in these subjects,
Kitab Muzan al-hikma was superior to anything written up to this point. Most importantly, alKhazini, in this book, was the first to propose the gravity of a body varies with its distance from
the center of the earth. Like much of al-Biruni’s works, this was not completely accurate. It was,
however, one of the first notions of changes in gravity and weight with relation to the center of
the earth. Al-Khazini derived this concept beginning with a strict definition of specific weight,
saying, “the magnitude of weight of a small body of any substance is in the same ratio to its
volume as the magnitude of weight of a larger body (of the same substance) to its volume." This
is the exact definition we use today. One reason Al-Khazini was able to come up with such an
accurate definition is that he was the first to show any knowledge that air had weight and this
weight increases in density with a change in altitude. It is known that he was aware of this
because he also discovered that water is denser when it is closer to the earth’s center, a fact that
would later be proven by Roger Bacon in the 13th century. In order to come up with this, he first
had to define weight. Al-Khazini called weight “a force inherent in solid bodies which causes
them to move, of their own accord, in a straight line towards the center of the earth and towards
this centre alone.” Once more, this is not absolutely correct, but it is fairly close. Using all of the
aforementioned facts, Al-Khazini theorized that the gravity of a body changes as it gets closer or
farther from the center of the earth. In his book, he says:
For each heavy body of a known weight positioned at a certain distance from the centre
of the universe, its gravity depends on the remoteness from the centre of the universe. For
that reason, the gravities of bodies relate as their distances from the centre of the
universe. The farther is a body from the centre of the Universe, the heavier it is; the
closer to the centre, the lighter it is. For that reason, the gravities of bodies relate as their
distances from the centre of the Universe.
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This concept of gravity was the starting point for our modern concept of gravitational potential
energy.
Al-Biruni and al-Khazini’s discoveries and methods changed the way science was
thought about. They were the first to apply experimental scientific methods to the fields of
hydrostatics and dynamics, which they unified to create the scientific field of hydrodynamics.
They also were the first scientists to study the science of gravity, (which would be further
developed in medieval Europe) generalizing the theory of centers of gravity and applying them
to three dimensional bodies. Without these two scientists who are often overlooked, the work
done by Newton and others would potentially never have occurred.
A third Islamic scientist, who actually did his work earlier than the previous two, was
influential in a very different field: optics. Before Abu Ali al-Hasan ibn al-Haitham, there were
two main theories on vision: the first, supported by Ptolemy and called the emission theory, said
that rays were emitted by the eye towards the object. Al-Haitham argued this was impossible
through the use of the stars: he said the distance from a star to the eye was too far for this to be
feasible. The second theory, called the intromission theory and supported by Aristotle, said that
physical forms emitted by the object enter the eye. Al-Haitham also thought this was inaccurate.
Instead, he argued that vision was different rays of light coming from each point on the object to
the eye, a much closer definition than either of the previous two. Through experimentation with
lens’, mirrors, refraction and reflection, he also found that light travels in a straight line. This was
all recorded in his book, Kitab al-Manazir (The Optics Thesaurus), an extremely influential book
for its time that introduced many of our modern concepts on optics, including the anatomy of the
eye. Eventually, a commentary was written by Kamal al-Din Abu’l- Hasan al-Farisi, which was
more frequently used by subsequent scientists than its predecessor.
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Al-Haitham made two other major contributions to the scientific world. The first, which
we still use today, was the use of the scientific method to obtain results. The second, which is
seemingly unrelated to optics, though still relevant, is that he was the first to theorize that a body
is in motion until something stops it. This is the beginnings of the concept of inertia, but alHaitham did not have any experiments to prove it, leaving the door open for Newton.
During the European Middle Ages, several factors contributed to the little exploration of
physics. The first was that the Church controlled all aspects of citizens’ lives and was against
science. Secondly, the economic recession that happened because of the Great Famine led most
people to solely focus on finding enough food to survive. Thirdly, The Bubonic Plaque killed
30% of the European population and isolated the remaining people in their own regions.
Without consistent communication, building ideas off or others’ experiments could not
effectively happen. This began to change with the European Crusades. Europeans who traveled
to the Middle East were exposed to the ideas of these Islamic scientists for the first time. These
ideas, new and exciting to the European Crusaders, were brought back to Europe and translated
so that they were accessible to educated Europeans, giving way to a whole new group of
scientists who emerged during the Renaissance. Four major scientists appeared, making their
most significant contributions in the field of astronomy: Nicolaus Copernicus, Galileo Galilee
Tycho Brahe and Johannes Kepler.
Copernicus, a polish scientist, lived from 1473-1543. Though there were other ideas, the
common belief of the time was in the Ptolemaic system, which, put generally, stated that the
earth is the center of the universe and all other planets moved in ‘epicycles’ around it.
Copernicus, however, disagreed with the Ptolemaic concept of equants and deferents. He says,
Yet the widespread [planetary theories], advanced by Ptolemy and most other
[astronomers], although consistent with the numerical [data], seemed likewise to present
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no small difficulty. For these theories were not adequate unless they also conceived
certain equalizing circles, which made the planet appear to move at all times with
uniform velocity neither on its deferent sphere nor about its own [epicycle's]
center…Therefore, having become aware of these [defects], I often considered whether
there could perhaps be found a more reasonable arrangement of circles, from which every
apparent irregularity would be derived while everything in itself would move uniformly,
as is required by the rule of perfect motion.
This first challenge of Ptolemaic ideas was a part of his Commentariolus, a small manuscript that
was only circulated, never printed in Copernicus’ lifetime. It is believed that Copernicus’
opposition to Ptolemy’s idea of equants is what prompted him to write Commentariolus. He was
exposed to and saw the flaws in Ptolemy’s system because at the time, he was working for the
church (one main reason he waited to publish his idea until right before his death) to reform the
calendar. The reason he had to reform this calendar was due to Ptolemy’s system. It is unknown
when Commentariolus was written, though based on later works, it is guessed that it was
probably sometime between 1508 and 1514. It was intended as an introduction to a later work, as
in it he says it is the “the mathematical demonstrations intended for my larger work should be
omitted for brevity's sake…” In it, he listed assumptions that he believed to solve the problems
of the current beliefs in astronomy. These included the concepts that the earth is only the center
of gravity and the moon’s orbit rather than the center of the universe, that all planets encircle the
sun (which is not in the center of the universe), the universe is much larger than it was previously
assumed to be, and the motion of the heavens, including the sun, is all due to the motion of the
earth. It also dealt with the correct order of the known seven planets (this was before Galileo, so
everything known about the universe had to be able to be viewed with the naked eye.)
Elaborations on his theory, called the heliocentric system, explained the motion of the planets
much more simply, and were published in his book, De revolutionibus (On the Revolutions),
published right around Copernicus’ in 1543 for fear of punishment from the church. The first
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book sets out the order of the planets, one of the strongest pieces of evidence for a heliocentric
universe. Copernicus says, “[The sphere of the fixed stars] is followed by the first of the planets,
Saturn, which completes its circuit in 30 years. After Saturn, Jupiter accomplishes its revolution
in 12 years. The Mars revolves in 2 years. The annual revolution takes the series' fourth place,
which contains the earth…together with the lunar sphere as an epicycle. In the fifth place Venus
returns in 9 months. Lastly, the sixth place is held by Mercury, which revolves in a period of 80
days.” This made the planets a unified system, established a relationship between the planet’s
distance from the sun and their periods, and corrected Ptolemy’s concept that since the universe
was geocentric, the sun, Mercury, and Venus all had the same period. This provided an
explanation for retrograde motion: Since earth is closer to the sun, it has a faster orbit. Thus, it
will sometimes overtake other planets farther from the sun, making it look as though the other
planets are moving backwards. Copernicus’ heliocentric system was not perfect (he believed
planets move in perfect circles at a constant speed), nor
was he able to prove it, but it was an extremely important
concept that would forever change the way astronomers
looked at the solar system.
Galileo, who followed Copernicus’ ideas, is
considered by many to be the father of modern science,
because he represents a turning point scientific history:
Figure 3 is a picture from Copernicus' original
publication. It shows that all bodies in our solar
system, with the exception of the moon, orbit
around the sun.
when observational experiments were used in addition
to thought and reason to prove nature’s laws. He is
most famous for discoveries in two fields: motion and
astronomy. His studies on motion began as a contradiction to Aristotle, who believed that heavier
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objects will always fall faster than lighter ones. To prove Aristotle wrong, Galileo dropped two
balls of different weights from the leaning tower of Pisa. As he suspected, both balls hit the
ground at the same time. Had Aristotle been correct, the heavier one would have hit the ground
first. In 1638, Galileo published a book that mathematically described his concepts of motion in
addition to the concept of friction.
The key piece of Galileo’s discoveries in astronomy was his
invention of the telescope in 1609. Using this, he was able to view things
that no one had before, and would be some of the strongest evidence for a
heliocentric system, something in which Galileo strongly believed. The
strongest piece of evidence for Copernicus’ theory was the discovery that Venus went through
phases like the moon, proving that it reflects the sun’s light and thus revolves around the sun.
Other important discoveries Galileo was able to make due to the presence of the telescope
include seeing the mountains and craters of the moon, viewing the rings of Saturn, and observing
the moons of Jupiter, proving Earth is not the only planet with a moon.
Another astronomer who expanded on the ideas of Copernicus was named Tycho Brahe.
He did not fully agree with Copernicus, nor did he disagree. Rather, he saw advantages in both
systems. He believed that physics would be undermined if Earth were not the center of the
universe, because heavy bodies fall to the center of the earth. On the other hand, the heliocentric
system had its advantages, such as a better explanation of lunar motion and explanation of
retrograde motion. So, Brahe created his own system. He put earth at the center of the universe,
so Aristotelian physics still made sense. The moon, sun, and stars revolved around the earth, but
the other planets revolved around the sun. This system was adopted by various astronomers
throughout the 17th century that could neither accept Ptolemy’s ordering of the planet, nor agree
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with Copernicus’ system for one reason or another (often, including in the case of Brahe, it was
for religious reasons).
Brahe made a number of other important contributions to astronomy. He revolutionized
astronomical instruments, was the first to observe celestial bodies throughout their orbits thus
discovering that planets do not always move in perfect circles, made corrections for atmospheric
refraction, and proved, through observations of comets that the atmosphere could change,
contradicting previous Aristotelian beliefs.
Following Brahe was Johannes Kepler. Though Brahe was Kepler’s mentor, Kepler
believed in the heliocentric system of Copernicus. However, he wanted to improve upon
Copernicus’ concepts. His first effort at this was trying to find a geometrical reason for the
distance between each planet and the sun. Unfortunately, this got him nowhere. His next try was
much more successful. By analyzing the orbits of various planets with a focus on Mars, Kepler
was able to establish three laws of planetary motion. First, planets move in an elliptical orbit
around the sun, rather than a perfect circle. Second, planets “sweep out” equal areas over equal
amounts of time. Third, the square of the time of a revolution is proportional to the cube of their
distance from the sun. These laws were influential in more than the astronomical world: Newton
used them to establish universal gravitation.
Kepler also made advances in the field of gravitation. He disagreed with Aristotle’s
theory on gravity, saying “gravity is a mutual tendency between material bodies toward contact,
so the earth draws a stone much more than the stone draws the earth. Heavy bodies are attracted
by the earth not because it is the center of the universe, but simply because it contains a lot of
material, all of which attracts the heavy body.” He realized that the tides occur because of
gravity, stating that "If the earth ceased to attract the waters of the sea, the seas would rise and
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flow into the moon..." and went on to add: "If the attractive force of the moon reaches down to
the earth, it follows that the attractive force of the earth, all the more, extends to the moon and
even farther..." Both of these statements are extraordinarily accurate applications of the concept
of gravity. He did, however, fail to realize that gravity plays a role in determining the motions of
the planets because he believed that a force must be acting upon the planets to keep them in
motion. Galileo disproved this years later through the use of projectiles. Newton then used this
information on projectiles and applied it to planetary bodies, a concept that is one of the
beginnings of the Newtonian Revolution.
The history of physics involves all aspects of ancient life. Without contribution made by
the Babylonians in written word and measurement, mathematical contributions from Euclid and
Pythagoras, and astronomical contributions by Thales all the way through Hipparchus, Physics
would not be important. Our history of Aristotle, Archimedes, Ptolemy, the European Middle
Ages, Early Islamic science, and the European Renaissance focus mostly on physics, but cannot
be completely understood without this other knowledge. The most important conclusion is that
all discoveries prior to the Newtonian Revolution were important because they allowed for
Newton to expand on them and allow the study of Physics to exponentially grow at an
unbelievable rate since that time.
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Works Cited
“Islamic Scientists." Al-Islam.org by the Ahlul Bayt DILP - Home. N.p., n.d. Web. 4 Oct. 2010.
<http://www.al-islam.org/encyclopedia/chapter11/4.html>.
"Abu Rayhan Biruni - Wikipedia, the free encyclopedia." Wikipedia, the free encyclopedia. N.p.,
n.d. Web. 4 Oct. 2010. <http://en.wikipedia.org/wiki/Abu_Rayhan_Biruni>.
"Abul Fath `Abd al-Rahman al-Khazini." Center for Islam and Science. N.p., n.d. Web. 4 Oct.
2010. <http://www.cis-ca.org/voices/k/al_khazini.htm>.
"Alhazen - Wikipedia, the free encyclopedia." Wikipedia, the free encyclopedia. N.p., n.d. Web.
4 Oct. 2010. <http://en.wikipedia.org/wiki/Alhazen>.
"Archimedes' principle (physics) -- Britannica Online Encyclopedia." Encyclopedia - Britannica
Online Encyclopedia. N.p., n.d. Web. 4 Oct. 2010.
<http://www.britannica.com/EBchecked/topic/32827/Archimedes-principle>.
"Aristotle's Physics." Smoot Group Cosmology. N.p., n.d. Web. 4 Oct. 2010.
<http://aether.lbl.gov/www/classes/p10/aristotle-physics.html>.
"Contributions of Ancient Arabian and Egyptian Scientists on the Development of Physics &
Technology - News Techno." News Techno. N.p., n.d. Web. 4 Oct. 2010.
<http://newstechno.org/contributions-of-ancient-arabian-and-egyptian-scientists-on-thedevelopment-of-physics-technology>.
"Galileo Galilei (Stanford Encyclopedia of Philosophy)." Stanford Encyclopedia of Philosophy.
N.p., n.d. Web. 4 Oct. 2010. <http://plato.stanford.edu/entries/galileo/>.
"Galileo and the Telescope ." Galileo and Einstein Home Page. N.p., n.d. Web. 4 Oct. 2010.
<http://galileoandeinstein.physics.virginia.edu/lectures/galtel.htm>.
"History of Physics." Astronomy Notes. N.p., n.d. Web. 4 Oct. 2010.
<www.astronomynotes.com/history/>.
Jones, Andrew Zimmerman. "Archimedes, Hipparchus, & Ptolemy - physics of the greeks
Archimedes, Hipparchus, & Ptolemy." Physics. N.p., n.d. Web. 4 Oct. 2010.
<http://physics.about.com/od/physicshistory/a/GreekPhysics_3.htm>.
"Legacy of Islam - Muslim Heroes and Personalities Glimpses of Renowned Scientists and
Thinkers of Muslim Era by H M Said." Ismaili Web by Nina Jaffer. N.p., n.d. Web. 4
Oct. 2010. <http://www.amaana.org/ISWEB/contents.htm#pos10>.
"More Kepler ." Galileo and Einstein Home Page. N.p., n.d. Web. 4 Oct. 2010.
<http://galileoandeinstein.physics.virginia.edu/1995/lectures/morekepl.html>.
"Nicholas Copernicus." Windows to the Universe. N.p., n.d. Web. 4 Oct. 2010.
<http://www.windows2universe.org/people/ren_epoch/copernicus.html&d=&frp=/windo
ws3.html&fr=f&sw=false&edu=mid&art=ok&cdp=/windows3.html&cd=false&back=/s
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earch/search_navigation.html>.
"Nicolaus Copernicus (Stanford Encyclopedia of Philosophy)." Stanford Encyclopedia of
Philosophy. N.p., n.d. Web. 4 Oct. 2010.
<http://plato.stanford.edu/entries/copernicus/#2>.
"Project MUSE - Technology and Culture - Sennacherib, Archimedes, and the Water Screw: The
Context of Invention in the Ancient World." Project MUSE. N.p., n.d. Web. 4 Oct. 2010.
<http://muse.jhu.edu/login?uri=/journals/technology_and_culture/v044/44.1dalley.pdf>.
"Renaissance Scientists." Yukon Education Student Network - Home. N.p., n.d. Web. 4 Oct.
2010. <http://www.yesnet.yk.ca/schools/projects/renaissance/scientists.html>.
"Stephen Hawking's Universe: Universes." PBS. N.p., n.d. Web. 4 Oct. 2010.
<http://www.pbs.org/wnet/hawking/universes/html/coper.html>.
"The Renaissance and the Scientific Revolution 1453." Mr. Van Overen's Virtual Classroom Welcome!. N.p., n.d. Web. 4 Oct. 2010.
<http://kvo27.com/renaissance_reading_packet.htm>.
"Tycho Brahe." Galileo and Einstein Home Page. N.p., n.d. Web. 4 Oct. 2010.
<http://galileoandeinstein.physics.virginia.edu/1995/lectures/tychob.html>.
"al-Khazini." Wikipedia. N.p., n.d. Web. 4 Oct. 2010. <en.wikipedia.org/wiki/Al-Khazini>.