Here are the numbered explanatory notes, and some commentary, regarding some of the discoveries in the timeline.
Cheers, Robert Lang
NOTES
(1) Very very few maps have survived from Ancient Greek times. As with the astronomical observations of the Greeks, the accuracy of their mapping continued to increase with the passing of the years. Eratosthenes (circa 275-194 BC) certainly had that knowledge of astronomy & geometry & mathematics which is necessary for the production of an accurate map of large parts of the surface of the Earth. Lamentably, his work is only known from secondhand accounts rather than from the original texts! It seems that the Sumero-Akkadians, probably the oldest civilization that has directly passed on many of its fundamental ways of thinking and organizing to modern Western Civilization, were already capable of making accurate plans of buildings and accurate town plans. But it seems that accurate smaller-scale (wider area) maps may have been beyond them. This e-book has chapters about ancient cartography:
http://www.press.uchicago.edu/books/HOC/index.htm
(2) The scribes & astrologers of the ancient Babylonian Empire also engaged in astrometry of the moon and planets. I have no idea how accurate they were.
(3) A lot of experts say that Leonardo da Vinci was the first accurate anatomist, but these experts tend to be from an arts background. How accurate, really, were Leonardo's anatomical drawings?
(4) Galileo is widely credited with heroically proving the heliocentric system, and the story of his interrogation by the Inquisition and his subsequent house arrest is well known, but the Cardinals were not fools and they knew that he did not have in his posession a mathematical proof of the correctness of a Sun-centred solar system.
(5) Antoine Lavoisier seems to be the first person who was doing exact chemical science in the modern sense, using concepts and procedures and nomenclature that we would recognize today. However, I have not assessed whether or not the credit for some of his discoveries should really be shared with other workers.
(6) Herschel's sky surveying and cataloging of non-stellar objects laid the essential groundwork for Galactic and Extragalactic astronomy, so it qualifies as a major advance in science.
(7) I have only listed Michael Faraday and Andre-Marie Ampere as discoverers of major advances in electromagnetism in the 1820s. But this was truly a golden decade for discovery in this field, and there were many other workers making important discoveries at this time, e.g. Ohm, Oersted, Arago, Biot, Savart, Poisson, etc. Here is a remarkably detailed and comprehensive timeline of advances in electricity and magnetism, not that I can vouch for its accuracy:
http://www.magnet.fsu.edu/education/tutorials/timeline/
(8) Several other parallaxes were published by other workers in the same year. However they were wrong!
(9) The invention of the telegraph had made this feasible.
(10) Any kind of exact knowledge of human and animal brains is at most 120 years old! Neurobiology, like molecular biology, is a
very recent science.
(11) What is nitrogen fixation? And
why will I
die if I don't know about it? See this article:
http://www.nature.com/scitable/knowl...ation-23570419
(12) The existence of the last Ice Age had become evident during the 19th C., but Penck and Bruckner provided abundant geological evidence to back up a plausible chronology for multiple glaciations and deglaciations.
(13) The Bohr model of the atom is also justifiably called the Rutherford-Bohr model.
(14) Kapteyn's now obsolete model of the Milky Way was that of a small galaxy with the Sun conveniently located near to its centre. While Harlow Shapley's model (in a series of papers between 1918 and 1919) greatly overestimated the diameter of our own Galaxy, it established the correct picture of our Milky Way Galaxy as a gigantic stellar system with the Sun's position a long way out from its centre.
(15) Cecilia Payne-Gaposchkin's 1925 PhD thesis is arguably the best in the entire history of astronomy, proving that the stars are made up of mainly hydrogen & helium. Even schoolchildren know that Newton discovered the laws of motion and Darwin discovered evolution, but it is
not well known that Payne-Gaposchkin
showed that hydrogen is the most abundant element in the universe.
(16) Harlow Shapley had taken the position that the Milky Way
is the entire universe, a view that was still tenable in the early 1920s. However, a 1929 paper by Edwin Hubble officially announced the first totally convincing resolution of the Andromeda Galaxy into stars & star clusters. Hubble also announced the discovery of many Cepheid variable stars within M31, and he used the Cepheid P-L relation to
calculate that M31 was at
8.5 times the distance of the SMC. While Hubble had already (in 1925 & 1926 papers) found some evidence that the "spiral nebulae" are likely to be vast stellar structures similar to our Milky Way Galaxy, his landmark 1929 paper about the Andromeda Galaxy convinced even the skeptics that this is the case. See for example:
http://adsabs.harvard.edu/abs/1999ApJ...525C.212C
In fact, Hubble certainly had not proved his case in 1923, though you will find this misinformation repeated again and again on the internet! It took a long time for astronomers to get comfortable with the idea that the universe contains multiple super-giant stellar systems comparable to the Milky Way. In fact, there was already hard evidence for this in the 19th Century; for example, William Huggins found that the spectrum of the Orion Nebula contained primarily emission lines from low-density gas and the spectrum of Messier 31 contained primarily absorption lines.....which have to be from cool gas in front of incandescent gas......stellar photospheres!
NOTES 17 to 26 in Next Post
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