PREFACE. 
vii 
which are alfo continued to each other , and hav- 
ing their proper Fluid the elaftic Aura or Air\ 
which are more fully explain d and conneBed 
in my fecond Lecture , together with an Account 
of Two Kinds of ^Equilibria proper to Mufcles , 
deducible from thefe Syjlems. 
VI. 
I have endeavoured. , as much as poffible , to 
be brief in my Explanation throughout the 
Whole ; avoiding every Digreffon that might 
in the leaf interrupt the Chain of my Reafon- 
ing : And as I have made fome ObjeBions to 
the fever al Opinions in my firjl LeBure , which 
I think they feemd liable to (in order the bet- 
ter to arrive at their uth, yet , with all poffible 
Regard to their Characters and Learning), the 
World is welcome to ufe me with the fiame Free- 
dom ; and indeed I fhall be always glad, if any 
Improvement arifes from fuch Objections to my 
Sentiment as the 'Judicious may juftly make \ 
