346.  The  mode  in  which  the  relative  dis-
tances moved  through  by  the  Power  and
the  Resistance  are  estimated,  will  be  under-
stood from  the  following  considerations :
Suppose  that  the  machine  is  turned  once
Fig.  65.  round,  so  as  to  unwind  some  cord  from  the

wheel.  Then  the  length  of  cord  which  is
thus  removed  from  the  wheel  is  equal  to  its  circumference  ;  and
this  expresses  the  distance  moved  through  by  the  power.  Also,
the  length  of  cord  which  is  at  the  same  time  wound  up  on  the
axle,  is  equal  to  its  circumference  ;  and  this  expresses  the  dis-
tance moved  through  by  the  resistance.  If,  for  instance,  the
circumference  of  the  wheel  is  12  inches,  and  the  circumference
of  the  axle  is  6  inches,  then  the  power  moves  through  J^-,  or
twice  as  much  space  as  the  resistance.  Therefore  the  mechanical
advantage  of  such  a  wheel  and  axle  would  be  2 ;  and  a  power
of  1  Ib.  applied  at  P,  would  raise  a  resistance  of  2  Ibs.  (nearly)
applied  at  W.
