late Difcoveries in Science. 127 



of the decompofition of forces. He then treats of the mo- 

 tion of a foHd body, whatever be its figure ; gives the con- 

 ditions of the motion of fluids, and appHes them to the mo- 

 tion of the waters of the fea and to that of the atmofphere. 

 He then determines what ought to be the force a£ling on the 

 celeftial bodies to render their movements fuch as they are 

 exhibited to our obfervation. The laws of Kepler conduct 

 him direftly to the principle of univerfal gravity ; that is to 

 fay, that the aftion which the celeftial bodies exercife on 

 each other is in the dire6l ratio of their malles and the in- 

 vcrfe of the fquare of their diftances. The new illuftrations 

 which he gives are highly worthy the attention of geome- 

 tricians. 



Fofl'ombroni has treated the principle of virtual forces 

 like an able geometrician. 



ASTRONOM7. 



Herfchel has publiflied his obfervations on the fatellites 

 of Jupiter, in which he determines the length of their days, 

 or their revolutions round their axes. The ^rft turns round 

 its axis in i day 18 hours 26' 6"; the fecond in 3 days 

 18 hours 17' 9"; the third in 7 days 3 hours 59' 6 '; and 

 the fourth in 16 days 18 hours 5' i'^. He endeavours to 

 determine the fize of thefe bodies, but has not yet been able 

 to attain to great accuracy. " We may only conclude," fays 

 he, " that the firft fatellite is larger than the fecond ; that 

 the fecond is the fmalleft of all ; that the third is much larger 

 than any of the reft ; and that the fourth is nearly as large as 

 the firft." 



Le Fran9ais Lalande continues with perfeverance his cata- 

 logue of the ftars of our hemifphere. He has already carried 

 the number to 49,000. 



Bouvard has completed a grand labour on the movements 

 of the moon. He has calculated the eclipfes mentioned by 

 I'tolemy, and thofe obfer^'ed by the Arabs. All thefe eclipfes, 

 compared with modern obfervations, have given him 13'' 21 

 of correction for the fynodical motion, and 8 '34'' 5 for the 

 njean anomaly. This agrees with the refults which Laplace 

 has found by calculation. 



5 The 



