280 
Mr.  E.  L.  Hancock  on  the  Effect  of  Combined 
hoped  that  the  law  of  the  lowering  of  the  elastic  limit  may  be 
determined.  The  modulus  of  elasticity  in  tension  has  also 
been  lowered. 
Fig.   4  shows   the    stress-strain  diagram    of    carbon-steel 
in    tension.     The    curve  C  represents   the    average    of   two 
Fig.  3. 
Nickel-Steel. — Tension  part  only  of  Torsion-Tension  Tests. 
Series  E. 
JS      EQ 
simple  tension  tests  of  the  material,  showing  an  elastic  limit 
of  34,000  lbs.  per  sq.  in.  The  curve  Ca  shows  the  result  of 
a  tension  test  made  while  the  specimen  was  held  at  one-third 
its  elastic  limit  in  torsion;  Cb  while  held  in  torsion  at 
two-thirds  its  elastic  limit ;  and  Cc  while  held  in  torsion  at 
its  elastic  limit.  These  curves  also  show  a  lowering  of  the 
elastic  limit  :  a  lowering  of  about  6  per  cent.,  30  per  cent., 
and  54  per  cent,  for  Ca,  Cb,  and  Cc  respectively.  It  will  be 
noticed  that  this  is  not  exactly  the  same  rate  of  lowering  as 
that  given  by  fig.  3.  The  modulus  of  elasticity  in  this  case 
does  not  seem  changed  in  the  case  of  Ca,  but  is  lowered 
considerably  in  the  case  of  Cb  and  Cc. 
In  all  cases  the  increase  in  the  troptometer  readings  while 
