74 - Mechanical Philosoplii/, [Chap. I, 



Dr. I lerschel, of Great Britain ; who, by the aid of 

 very powerful and accurate instruments, and with 

 the skill and perseverance for which they are so 

 eminently distinguished, have made surprising pro- 

 gress in investigating this department of the lunar 

 phenomena. 



A\'hen Newton died, several of the inequalities 

 of the planetary motions, arising from the disturb- 

 ing forces of various bodies, were with difficidty 

 reconciled with the astronomical principles which 

 he had laid down. These inequalities have been 

 successively investigated since that time, their 

 causes ascertained, their laws fixed, their perfect 

 consistency with the Newtonian theory demon-, 

 strated, and thus a very formidable objection to 

 that theory satisfactorily removed. — It is known to 

 mathematicians, that this celebrated philosopher, 

 calculating the effect of the sun's force in pro- 

 ducing the precession of the equinoxes^ fell into an 

 errour, and made it \^'i,'&, by one half, than the 

 truth. The true quantity of this motion was first 

 determined by M. d'Alembert, in 1749^ who 

 also, in the course of his inquiries, more fully ex- 

 plained the nutation of the eartKs axisy which had 

 been discovered a few years before by Dr. Brad- 

 ley. With no less diligence the inequalities in 

 the revolutions of all the planets, and especially 

 of Jupiter and Saturn, have been examined, ascer- 

 tained, and reduced to regular principles. lu 

 these difficult investigations, many astronomers 

 have employed themselves, in the course of the last 

 century, and by their labours rendered important 

 services to this science , but, perhaps, none of the 

 number deserve more honourable distinction than 



