836 THE POPULAR SCIENCE MONTHLY. 



1651, on the quadrature of the hyperbola, ellipse, and circle, following 

 it with a criticism of Pere Gregory de Saint Vincent's treatise on the 

 same subject, and, three years afterward, with his discoveries on the 

 magnitude of the circle {de circuli magnitudine i/iventa nova). 



In 1655 he went to France, and received a degree in law from the 

 Protestant Academy at Angers. Returning to Holland, he engaged 

 with his brother in the manufacture of large lenses. With one of 

 these, an objective of twelve feet focal distance, he discovered the first 

 satellite of Saturn (the sixth in the order of distance), and announced 

 the fact, after the manner of his time, in an anagram. It is said that, 

 in the excitement attending his achievement, he engraved his anagram 

 upon the glass itself by the aid of which the discovery was made. He 

 afterward made glasses with one hundred, one hundred and seventy, 

 and two hundred and ten feet of focal distance, which could not be 

 inclosed in a telescopic tube on account of the swagging, to which so 

 long an instrument would be subject, but for which he contrived a 

 kind of framework support, while the observer stood at the focal point, 

 eye-glass in hand. The necessity of using such cumbrous contriv- 

 ances has happily been dispensed with by the introduction of reflect- 

 ing telescopes. 



In 1656, Huygens published, in Dutch, a memoir on the calcula- 

 tion of probabilities, for which Pascal and Fermat had prepared the 

 way, and which was translated into Latin by his preceptor, Schooten, 

 to be inserted as an appendix to his " Mathematical Exercises," in 

 illustration of the usefulness of algebi'a. In the same year he invented 

 the escapement of watches and clocks. Galileo had already recognized 

 the synchronism of the motion of pendulums, and experimenters had 

 begun to avail themselves of it in timing their observations ; but they 

 knew of no better way of using the pendulums than to employ a man 

 to keep them in motion and count their vibrations. Huygens con- 

 nected them with clock-work, very much as we now have them, and 

 made the whole operation automatic. 



In 1659, having constructed an objective of twenty-two feet focal 

 distance, Huygens turned his attention to Saturn's ring, which Galileo 

 had perceived but dimly, discovered its true character, calculated its 

 elements, and predicted its temporary disappearancee in 1671 ; a pre- 

 diction which his fellow-astronomers saw fulfilled twelve years after it 

 was made, with great admiration for his genius. In his work, giving 

 an account of these observations, " Systema Saturninum," he also de- 

 scribed the nebula in Orion, and the bands of Jupiter and Mars, an- 

 nounced that the fixed stars had no perceptible diameter, and made 

 known his device for measuring the apparent diameters of the planets, 

 an incipient micrometer. He discovered but one of the satellites of 

 Saturn, and did not seem to care to look for any other ; for his enter- 

 prise in this direction was bound by the opinion he entertained that 

 there was a relation between the number of planets and of satellites ; 



