liISCOVERIES IN THE CELESTIAL SP \CES. 317 



the Novum Organon. The invention of the telescope, an5 

 the greatest discoveries in physical astronomy (viz., Jupiter'a 

 satellites, the sun's spots, the phases of Venus, and the remark- 

 able form of Saturn), fall between the years 1609 and 1G12. 

 Kepler's speculations on the elliptic orbit of Mars=* were be- 

 gan in 1601, and gave occasion, eight years after, to the com- 

 pletion of the work entitled Astroiiomia nova seu Phijsica ce- 

 testis. " By the study of the orbit of Mars," writes Kepler, 

 *' we must either arrive at a knowledge of the secrets of astron- 

 omy, or forever remain ignorant of them. I have succeeded, by 

 untiring and continued labor, in subjecting the inequalities of 

 the movement of Mars to a natural law." The generaliza- 

 tion of the same idea led the highly-gifted mind of Kepler to 

 the great cosmical truths and presentiments which, ten years 

 later, he published in his work entitled Harmonices Miaidi 

 lih'i quinque. " I believe," he well observes in a letter to 

 the Danish astronomer Longomontanus, " that astronomy and 

 physics are so intimately associated together, that neither can 

 be perfected without the other." The results of his researches 

 on the structure of the eye and the theory of vision appeared 

 in 1604 in the Paralipoinoia ad Vitellionein, and in 161 If 

 in the Dioptrica. Thus were the knowledge of the most im- 

 portant objects in the perceptive world and in the regions of 

 space, and the mode of apprehending these objects by means 

 of new discoveries, alike rapidly increased in the short period 

 of the first ten or twelve years of a century which began with 

 Galileo and Kepler, and closed with Newton and Leibnitz. 



The accidental discovery of the power of the telescope to 

 penetrate through space originated in Holland, probably in tlie 

 closing part of the year 1608. From the most recent investi- 

 gations it would appear that this great discovery may be 

 claimed by Hans Lippershey, a native of Wesel and a spec- 

 tacle maker at Middleburg ; by Jacob Adriaansz, surnamed 

 Metius, who is said also to have made burning glasses of ice ; 

 and by Zacharias Jansen.t The first-named is always called 



* Delambre, Hist, de V Astroyiomie Ancienne, t. ii., p. 381. 



t See Sir David Brewster's judgment on Kepler's optical works, in 

 the " Martijrs of Science,'' 1846, p^ 179- 182. (Compare Wilde, Gesch. 

 der Optik, 1838, tli. i., s. 182-210.) If ihe law of the refraction of tha 

 rays of light belong to Willebrord Snellius, professor at Leyden (1626), 

 who left it behind him bm'ied in his papers, the publication of the law 

 in a trigonometrical form was, on the other hand, first made by De» 

 cartes. See Brewster, in the North Bnhsk Review, vol. vii., p 207 ; 

 VVilde, Gesch. der Optik, th. i., s. 227. 



I Compare two excellent treatises on the discovery of the tele&ccpe 

 by Professor Moll, of Utrecht, in the Journal of the Royal Institution, 



