ASTRONOMY, ETC., OF SEVENTEENTH CENT. 207 



FIG. 90. TELESCOPIC APPEARANCE OF SATURN. 



other position with regard to the earth, changed into the appearance 

 of a pair of long handles, and ultimately into the form of the ends of 

 a narrow ellipse. In 1656 Huyghens published his discovery in the 

 anagrammatic form which was the fashion of the time. The letters 

 of the anagram when transposed gave the announcement, as he showed 

 afterwards, that Saturn is surrounded by a thin flat ring inclined to the 

 ecliptic, and not joined to the planet. Huyghens also first discovered 

 a satellite of Saturn; and he appears to have convinced himself that 

 there could be no more, by a reason which appears now very curious, 

 namely, that the number of secondary planets of the 'solar system was 

 by his discovery raised to six, and as that was the number of the pri- 

 mary planets, the number of satellites must be complete. The dis- 

 ;ry by Cassini in 1671 of other satellites of Saturn brought this 

 . I of speculation into discredit. 



Among the discoveries and mechanical inventions of Huyghens, 

 none is more noteworthy than his application of the pendulum to re- 

 gulate the motion of clocks. The uniform duration of the oscillations 

 of a pendulum was discovered, as we have already seen, by Galileo. 

 It was Huyghens who devised the well-known arrangement by which 

 the oscillations of the pendulum are made to control the motion of 

 the clock. Fig. 91 will render the mechanism intelligible even to a 

 person who has never examined the movements of an ordinary clock. 

 T T is the rod of the pendulum attached to a fixed support at a, and 

 bearing at its lower end the large mass , called the bob of the pen- 

 dulum. When a pendulum of this kind is made to swing backwards 



