370  Mr.  J.  Morrow  on  the  Lateral  Vibration 
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Section  VI.   Correction  for  Rotatory  Inertia. 
§  24.  Hitherto  the  terms  depending  on  the  angular  motion, 
both  of  the  concentrated  masses  and  of  the  sections  of  the 
bars  themselves,  have  been  neglected.  This  is  equivalent  to 
supposing  the  inertia  o£  each  element  to  be  concentrated  at 
its  centre. 
The  effect  of  the  angular  acceleration  of  the  bar  is 
sufficiently  small  to  be  neglected  in  practice,  but  in  the  case 
of  a  concentrated  mass  the  additional  terms  may  be  important. 
There  are  various  methods  of  procedure.  An  important 
approximate  one  being  to  assume  in  the  first  place  that  the 
type  of  vibration  is  unaltered  by  rotatory  inertia  and  then  to 
find  the  correction  due  to  this  cause. 
