580 PHILOSOPHICAL TRANSACTIONS. [aNNO I76I. 



viate in part, the difficulty of such intricate calculations, he has supposed the 

 orbits of the earth and Venus to be originally circular, and to suffer no other alter- 

 ation but what is occasioned by their mutual attraction, and the attraction of the 

 other planets. Where the forces of two planets are considerable with respect to 

 each other, as in the case of Jupiter and Saturn, it may be necessary in such 

 computations to have regard to the excentricity of their orbits ; and this may be 

 reserved for a subject of fliture scrutiny. But the supposing the orbits of the 

 earth and Venus to be circular, may, in the present case be admitted without 

 difficulty, as the forces of these two planets are so small, and the excentricity of 

 iheir orbits not considerable. On these grounds therefore he has computed 

 the variations which are the effects of the earth's action : 1 st, the variation of 

 Venus's distance from the sun ; 'Zdly, that of its place in the ecliptic ; 3dly, the re- 

 trograde motion of Venus's nodes ; and4thly, the variation of inclination of its orbit 

 to the plane of the ecliptic. 



The similar irregularities in the motion of the earth, occasioned by its gravita- 

 tion to Venus, are here likewise computed : but it is to be observed, that the abso- 

 lute quantity of these irregularities is not here given, it being impossible, at 

 present, to do it ; because the absolute force of Venus is not known to us. He 

 has therefore stated that planet's force by supposition, and has accordingly com- 

 puted the effects it must produce : with the view that the astronomers may 

 compare their observations with the motions so calculated, and from thence dis- 

 cover how much the real force differs from that which has been supposed. But 

 the exact determination of the force of Venus must be obtained by observations 

 made on the sun's place, at such times when the effect of the other planets is 

 either null or known. 



The influence of Venus on the earth being thus computed, that of the other 

 planets on the same may likewise hereafter be considered : by which means, the 

 different equations, that are to enter into the settling of the sun's apparent place, 

 will be determined ; the change of the position of the plane of the earth's orbit 

 will also be known ; and consequently the alteration that thence arises in the 

 obliquity of the ecliptic, and in the longitude and latitude of the fixed stars. 

 These matters of speculation are reserved for another occasion, in case what is here 

 offered should deserve approbation. But the later more accurate calculations and 

 astronomical observations have rendered a further account of this elaborate paper 

 unnecessary. 



LIIl. An Account of a Treatise in French, presented to the Royal Society, 

 tntitled, Lettres sur I' Electriciti, by the Abb} Nollet, Member of the Royal 

 Academy of Sciences, &c. ^c. By William Watson, M.D., F.R.S. p. 336. 



About 8 years since, the learned and ingenious author of the work before us 



