206 HISTORY OF SCIENCE. 



cember in the same year; but Gassendi in vain observed the sun 

 several days before and after that date. A transit of Venus actually 

 occurred, and it was seen by no mortal but by two young English- 

 men, natives of Lancashire. One of these, JEREMIAH HORROCKS, had 

 undoubtedly so great a genius for scientific work, that his premature 

 death in 1640, at twenty years of age, must be regarded as a great 

 loss to science. Horrocks had discovered some errors in the pub- 

 lished tables, and he calculated that on the 4th of December, 1639, 

 there would, contrary to the showing of Kepler's tables, be a transit 

 of Venus, the precise hour for which he calculated. He wrote to a 

 friend named Crabtree, asking him to observe the sun with a telescope 

 at the time he named. The event realized his predictions, and these 

 two young men had the satisfaction of observing the first transit of 

 Venus ever witnessed. The importance of these transits of the in- 

 ferior planets across the sun's disc, as phenomena confirming the 

 Copernican theory is sufficiently obvious. 



The next name to be mentioned is that of HUYGHENS, who held 

 one of the highest places as a mathematician, an astronomer, and a 

 physicist. He was born at the Hague on the 4th of April, 1629, and 

 being intended for the legal profession, he was pursuing his studies at 

 Leyden when he was attracted to mathematical learning, and soon 

 made himself master of even the most difficult branches of the Carte- 

 sian geometry. His reputation in mathematics became so high that in 

 1655, when the Academy of Sciences at Paris was instituted, Louis 

 XIV. invited him to reside in that capital, and he continued from 1666 

 to 1 68 1 to enrich the Memoir es of the French Academy with a number 

 of remarkable papers. At the revocation of the Edict of Nantes he re- 

 turned to Holland, where he continued his scientific labours, and died 

 on the 5th of June, 1695, in the sixty-fifth year of his age. One of 

 the first of Huyghens' astronomical discoveries was that of the real 

 figure of Saturn, the nature of which had been a puzzle to all preced- 

 ing astronomers. He had given much attention to the art of grinding 

 and polishing the lenses of telescopes, and he had succeeded in fabri- 

 cating some excellent object-glasses of a very great focal length. He 

 constructed a telescope of 23 feet focal length, with which he made 

 the discovery of Saturn's real form, and subsequently he made other 

 telescopes of much greater length. The difficulties of handling a tele- 

 scope of so great a length were partly overcome by suppressing alto- 

 gether the tube of the ordinary instrument, which, though the most 

 conspicuous part of the telescope, is by no means essential. 



When Galileo first turned his telescope to Saturn, he was astonished 

 to find that planet accompanied, as it appeared to him, by two con- 

 tiguous bodies, which he poetically compared to servants aiding Saturn 

 in his old age. The nature of these adjuncts defied all his conjectures 

 until forty years afterwards, when Huyghens saw Saturn with what 

 appeared at first a line of light, which, as the planet passed into an- 



