50 ESSAYS ann OBSERVATIONS 
which impells them towards the fun, as to 
endue this fuppofed aether with a power 
which repells it from the fun, Therefore 
the argument which is juftly urged by this 
author himfzlf againft a plenum in the 28th 
query, at the end of his opticks, may be ur- 
ged with equal fuccefs againft this fuppofed 
aether, ‘* It is of no ufe ; and, as there isno 
‘‘ evidence for its exiftence, it ought tobe 
¢¢ sejected,”” 
I muft own, at the fame. time, great re- 
luctance, to embrace a doctrine which over- 
turns, or feems to overturn, the moft beau- 
tiful part of Sir J/aac’s own theory, and that 
which affords the ftrongeft conviction of. its 
truth, wz. the connexion, by a common 
caufe, betwixt the curvilinear motion of the 
planets, and the defcent of bodies towards 
the center of this earth. Suppofing an ae- 
therial medium to be the caufe of the former, 
it cannot well alfo be the caufe of the latter. 
Among other reafons, this occurs, that the 
different denfities of the fuppofed aether, 
on the oppofite fides of a bit of. matter left 
free in the air, muft be, quam proxime, no- 
thing. This muft be yielded ; and the con- 
fequence is, that the bit of matter involved in 
a 
4 
