426 



ILLUSTRATIONS OF THE 



circumference, they muft produce a retardation 

 in the diurnal revolution ; and from this muft 

 arife ari inequality, not uniformly progreffive in 

 the fame diredlion, but periodical, and confined 

 within certain limits, as the caufes are by which 

 it is produced *. 



377. Mr 



f 



ies from a higher to a 

 earth, the whole ten- 

 dency is not to increafe the velocity of the eartlVs rota- 

 tion, and many compenfations take place, which, when 

 the matter is conflclerecl onlj in general, are neceflarily 

 OYerlooked. This will appear evident, if we refleft,* 

 that it is not fimpl j the approach of a body towards the 

 centre of the earth, or its removal from that cqntre, 

 ivhich tends to dillurb the rotation of the earth j but itg 

 approach to the axis of the earth, or its removal from 

 that axis. The velocity with which a particle of mat- 

 ter revolves, whether on the farface, or in the interior 

 ©f the globe, is proportional to its diftance from the 



+ 



axis of rotation ; and therefore, when a body comes 

 nearer to the axis, it lofes a part of the motion which it 

 had before ; which part, of confequence, is communica- 

 ted to the whole mafs of the earth, and therefore tends 

 to increafe the velocity with v/hich it revolves. The 

 contrary happens when a body recedes frona the axis ; 

 for it then receives an addition to its velocity, which, 



Tom the rotatory motion 



earth. 







Hence, bodies moving in a horizontal plane, may m- 



creafe or diminilh the fwiftnefs of the diurnal motion, 



according 



I 



