PREFACE 
/ N the Year 1733 I publifhed an Ejjay on 
Mufcular Motion , founded on the New- 
tonian Philofophy of Attra&ion and Repul - 
fion ; and though the thoughts were hafiily put 
together , and the Performance in general, 
very inaccurate , yet I mufi own I have not 
met with any Reafen , fence that ‘Time , to alter 
my Sentiments in regard to the Caufe and Mari- 
ner of ContraBion in the mufcular Fibres. 
I did not think indeed of ingaging my f elf any 
further in folving fuch abjlrufe Phenomena ; 
but being defined by my ever honouredFriend Sir 
Hans Sloane Baronet , to make feme Experi- 
ments which might illuflrate and confirm the 
Truth of my Hypothecs, I readily and chear- 
fully complied with his Commands \ and after- 
wards I drew up the following Le&ures , 
vdhich were by Order of the Prelid ent and 
Council read before the Royal Society, as 
the Croonean Le&ures for the Year 1747. 
purfuant 
