5 3 Mr.  button  on  the  initial 
time  anfwering  to  a certain  number  of  vibrations,  the 
finding  of  the  center  of  ofcillation  is  eafy : for  if  <v  de- 
note the  number  of  vibrations  made  in  s feconds,  then  it 
is  well  known,  that  as  vv  : ss  : : 39.2  : 
39-2*5 
V v 
= the  dif- 
A/ 
a 
. 
/ 
t 1 ■ 
J 1 
|. 
B y 
J 
tance  in  inches  from  the  axis  of  motion  to  the  center  of 
ofcillation ; and  by  this  rule  the  place  of  that  center  was 
found  for  each  day. 
The  center  of  gravity  was  afcertained  by  one  or  both 
of  the  two  following  methods.  Firft, 
a triangular  prifm  of  iron  ab,  being 
placed  upon  the  ground  with  an  edge 
upwards,  the  pendulum  was  laid 
acrofs  it,  and  moved  forward  or  backward  on  the  Item  or' 
block  as  the.  cafe  required,  till  the  two  ends  exactly  ba- 
lanced each  other;  then,  as  it  lay,  the  diftance  was  mea- 
fured  from  the  middle  of  the  axis  to  the  part  which 
refted  on  the  edge  of  the  prifm,  or  the  center  of  gravity 
of  the  pendulum.  The  other  method 
was  as  in  the  latter  of  the  two  annexed 
figures,  where  the  ends  of  the  axis  being 
fupported  on  fixed  uprights,  and  a chord 
fattened  to  the  lower  end  of  the  pen- 
dulum, was  patted  over  a pulley  at  p,  dif- 
ferent weights  w were  fattened  to  the 
other  end  of  it,  till  the  pendulum  was 
brought 
r\ 
