for the libration of Antagonifl Mufcles. This libration be- 
tween other Mufcles is anfwer'd by the MTe/^^^-of the in- 
cumbent Atmofphere, which preffes upon the Thorax and 
other Parts of the Body, And, as in all other voluntary 
Motions the influence of the Will only gives a Prevalence 
to one of two Powers before equilibrated, fo here it ferves 
to enable thofe Mufcles to lift up a Weight too ponderous 
for their ftrength not fo afEfted 5 and therefore as foon as 
that affiftance is withdrawn, the are again deprefs'd 
by the meer Gravitation oi the At^ofphere^ which wou'd 
otherwife remain elevated thro the natural tendency of 
thofe Mufcles to contradion. 
This is evidently proved from the Torricel/ian exptn- 
ments, and thofe made upon Animals in Mr Boyle s En- 
gine 5 where, as foon as the Air is withdrawn, and the 
prejfnre th^xehy taken off, the Intercoftal Mufcles and Dia- 
phragm are contracted, and the Ribs elevated in an inftant, 
and can't by any power of the Will be made to fubfide, 
till the Air is again let in to bear 'em forcibly down. 
It were fcarce worth while to take notice here of a Mi- 
ftake of the Learned Dr WH/k, were it not for the Great 
Authority of the Man, which is almoft fufficient to keep 
Error in countenance. The Dr having obferv'd that the 
0$^%^^^^^^ the External and Internal Intercoftal Mukks rm 
uju. in a contrary order, as it were, dccuCfating each other, takes 
cccafion from thence to fancy, that there was an oppofition 
in their Office, and that as the External ktvd to raife up 
the Ribs, the Internal drew 'em down again, forgetting at 
that time. That, when a contraftile Body is faften'd at 
the feveral ends to Points unequally. movable, let the Cori- 
traftion happen in what part or manner foever, the mofe 
movable Point muft be drawn towards the left movable : 
By which rule, whether External ox iMernal li^^ 
contrafted, the lower Ribs WilF^^ 
upper, that is, be rais'd tijp. 
As 
