Claudius
Ptolemy (fl. 2nd century CE) was a Roman astronomer who wrote the highly influential
astronomical work, the Almagest. Ptolemy worked from the assumption
(shared by Europeans dating back to Aristotle and earlier) that the earth
was the center of the universe, and that the sun, planets, and stars revolved
around it. (This conception of the universe is called geocentrism.)
When early astronomers observed the actual motions of the planets (without
telescopes, no one could see stars moving yet), though, they realized that
planets do not move in perfect circles around the earth as Aristotle thought.
How to explain this? Ptolemy came up with a complicated set of devices that
would account for observed planetary motions while still maintaining a geocentric
universe. (This move, in which one fiddles with a theory in order to accommodate
rogue data, is often called “saving the phenomena.”)
Now
this gets a little complicated, but what you should notice about the account
below are the contortions Ptolemy was willing to go through in order to wedge
the planet’s observed movements into a geocentric system.
Ptolemy used three basic constructions,
the eccentric, the epicycle, and the equant (shown in that order above).
In an eccentric construction, the Earth, E, is displaced slightly
from the center, C, of the planet’s orbit. In the second construction, the
planet moved on a little circle (an epicycle) the center of which
rotated on the circumference of the large circle centered on the Earth. This
helped explain why from the Earth planets sometimes appeared to move backward
(retrograde motion). In the case of the equant, the center of construction
of the large circle was separated from the center of motion of a point on
its circumference, as shown below, where C is the geometrical center of the
large circle (usually called in these constructions the excentric circle)
but the motion of the center of the epicycle, O, is uniform about e, the
equant point.
Ptolemy
combined all three constructions to explain the motions of the planets, Sun,
and Moon. A typical model of a planetary orbit (combining eccentric, epicycle,
and equant) might look like the picture below, where E is the Earth, C the
geometric center of the eccentric circle, Q the equant point, F the center
of the epicycle, and P the planet. What a mess!
[Some material paraphrased from Al van Helden’s Galileo Project; images from Michael J. Crowe, Theories of the World from Antiquity to the Copernican Revolution]
It ought not to be disputed that rational nature was made holy by God, in order to be happy in enjoying Him. For to this end is it rational, in order to discern justice and injustice, good and evil, and between the greater and the lesser good. Otherwise it was made rational in vain. But God made it not rational in vain. Wherefore, doubtless, it was made rational for this end. In like manner is it proved that the intelligent creature received the power of discernment for this purpose, that he might hate and shun evil, and love and choose good, and especially the greater good. For else in vain would God have given him that power of discernment, since man’s discretion would be useless unless he loved and avoided according to it. But it does not befit God to give such power in vain. It is, therefore, established that rational nature was created for this end, viz., to love and choose the highest good supremely, for its own sake and nothing else.
garden at Montpellier (established 1593)
Descartes’ vortex theory, which Desaguliers calls a “physical Romance,” is ...
Condemned in England
but believed in France
For the bold
Britons who all tyrants hate
In Science as
well as in the State
Examined with
experimental eyes
The vortices
of the Cartesian skies
Which tried
by Facts and mathematick Test
Their inconsistent
principles confess’d...
But tow’ring
Genius, from its certain cause
Ev’ry appearance
a priori draws
And shows the
Almighty Architect’s unalter’d Laws
That Sol self-pois’d
in aether does reside
And there exerts
virtue far and wide
Like Ministers
attending ev’ry glance
Six worlds sweep
round his Throne in mystic dance
He turns their
motion from its devious course
And bends their
orbits by attractive force
His power coerc’d
by Laws, still leaves them free
Directs but
not destroys their Liberty...
And reigning
thus with limited Command
He holds a lasting
scepter in his Hand
By his example
in their endless race
The primaries
lead their satellites
Who guided,
not enslaved their orbits run
Attend their
chiefs, but still respect the Sun
Salute him as
they go and his dominion own.
a. modern genetics developed out of a combination of biochemistry & classical (Mendelian) genetics
i. biochemistry = 1 of several approaches in the 19th & 20th centuries
for understanding cell-level processes of life
(1) an alternative to biochemical approach: many embryologists described
the development they saw under microscope without chemical analysis
ii. 1870s-80s: several key cell-level discoveries
(1) acid substances in nucleus (later called nucleic acid)
(2) chromosomes (thread-like structures in cell’s nucleus)
(a) Weismann speculated that these contained the units of heredity
iii. 1920s-30s: deepening of knowledge of chromosomes
(1) genes arranged on line in chromosomes
(2) chromosomes consist of DNA, protein – most thought that proteins contained
genetic info
b. molecular revolution
i. molecular revolution = study of inheritance + focus on structure of genetic
material (new focus & indebted to physics/chemistry)
(1) in other words, combines:
(a) biochemistry (looking at chemical processes at cell level as way of
understanding development) w/...
(b) Mendelian genetics
* organism carries & transmits to its offspring a set of hereditary
elements (genes)
* each gene determines a single characteristic
ii. 1953: Watson & Crick
(1) argued that genetic info all inside DNA & that DNA molecule shaped
like double helix
(2) argued that once structure known, could then figure out how DNA broke
up & re-formed during creation of new cells & ultimately new organisms
iii. importance of physics to molecular revolution
(1) unusual for biologists before this to think w/mechanical models – more
typical for physics (where Watson coming from)
(2) X-rays used to detect structure of living molecules & ultimately
DNA (Franklin)
c. Human Genome Project (HGP)
i. HGP = scientific research effort to analyze DNA of humans & several
other organisms
ii. begun in US in 1990 under sponsorship
of Department of Energy & National Institutes of Health (NIH)
iii. related programs begun in several other countries in coordination w/US
program
iv. goals
(1) identify chromosomal location of every human gene
(2) determine each gene’s precise chemical structure in order to...
(3) elucidate its function in health & disease
(4) address ethical, legal & social implications of the information
obtained
v. HGP competing w/commercial enterprises, which have beat HGP to the punch
on mapping code
During a visit that German physicist Werner Heisenberg took to the United States in the late 1920s, he had the following conversation about his uncertainty principle with an American physicist:
American: You Europeans, and particularly you Germans, are inclined to treat such new ideas as matters of principle. We take a much simpler view.... Perhaps you make the mistake of treating the laws of nature as absolutes, and you are therefore surprised when they have to be changed.... I believe that once all absolutist claims are dropped the difficulties will disappear by themselves!
Heisenberg: Then you are not at all surprised that an electron should appear as a particle on one occasion and as a wave on another? As far as you are concerned, the whole thing is merely an extension of the older physics, perhaps in unexpected form?
American: Oh no, I am surprised; but, after all, I can feel that it happens in nature, and that’s that.
– source: Gerald
Horton, “The Formation of the American Physics Community
in the 1920s and the Coming of Albert Einstein,” Minerva 19 (1981):
569-81.