ASTRONOMY IN SHAKESPEARE'S TIME— ABBOT X15 



The second epoch was ushered in by the theory of Copernicus. By 

 the invention of the telescope and the mechanical clock, great physical 

 aids became available for observation. Printing, that greatest agency 

 of human culture, had been invented. Mathematics, which in the 

 first epoch grew to comprise arithmetic, algebra, geometry, and trig- 

 onometry, received in the second epoch not only the introduction of 

 logarithms but the superpowerful reinforcement of the calculus which 

 was invented by those great geniuses. Sir Isaac Newton and Leibnitz. 

 Besides these great names already mentioned, Tycho Brahe, Kepler, 

 Galileo, La Place, Bradley, the Herschels, and many others of nearly 

 equal fame immortalize this epoch. The laws of Kepler, interpreted 

 by Sir Isaac Newton in his theory of gravitation, were outstanding 

 triumphs of theory. Bradley, with his discovery of aberration of 

 light and his catalogs of star places, was the apostle of an accuracy 

 almost modern. 



At the beginning of the third epoch, about 1810 to 1840, stand four 

 invaluable discoveries and one revolutionary observation. Photog- 

 raphy, the spectroscope, the wave character of light, and improved 

 optical glasses were the four discoveries, and the first measurement of 

 the immense distance of one of the nearest stars by Bessel was the 

 revolutionary observation. Bessel's measurement in 1837 gave an un- 

 impeachable standing to the system of Copernicus. Prior to that time 

 everyone who accepted the view of Copernicus, that the earth re- 

 volves about the sun, had to accept on faith the proposition that all 

 the stars are so immensely distant that they are shifted on\j im- 

 perceptibly in apparent position by the displacement of the earth in 

 its revolution round the sun through nearly 200,000,000 miles each 6 

 months. Bessel measured such a shift. It corresponded to a star 

 distance of 60 trillion miles. How astonishing must have seemed this 

 tremendous extension of the universe to those to whom this immense 

 distance first stood undeniably revealed ! The improvements in op- 

 tical glass led in this epoch to the construction of large achromatic 

 refracting telescopes of short enough focus to be manageable. The 

 older telescopes had required an excessive focal ratio to avoid spheri- 

 cal aberrations and were terribly unwieldy. Thus great power was 

 added to eye observations. The diffraction grating for spectroscopic 

 work was perfected by Angstrom and Rowland. Photography, how- 

 ever, was delayed in coming to its own for astronomical use until near 

 the beginning of the fourth astronomical epoch in which we now 

 live. Spectrum analysis disclosed the chemistry of the sun and stars 

 at the middle of the nineteenth century. Here again was something 

 almost incredible: That we should ever know the composition of 

 bodies trillions of miles away ! 



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