452  Mr.  A.  0.  Rankine  on  the  Decay  of 
III.  Results. 
The  curves  shown  in  figure  3  are  copied  from  the  experi- 
mental curves.  The  break  in  the  curve,  which  probably 
indicates  the  point  at  which  the  elastic  limit  is  reached,  will 
Fig.  3. 
500 
0  1  2  3  4 
7>Af£   ///  //OURS. 
be  noticed  in  the  cases  of  the  3*4,  4*0.  4*2,  and  4*4  per  cent, 
specimens.  It  was  not  found  practicable  to  maintain  the 
temperature  constant  for  a  sufficient  time  to  obtain  such  a 
break  in  the  4*5  per  cent,  curve.  It  will  be  seen,  too,  that 
these  points  lie  on  a  curve  which,  from  theoretical  con- 
siderations, must  pass  through  the  point  t  =0  W=500.  For 
in  the  limiting  case  when  the  substance  possesses  no  elasticity, 
it  follows  that  it  has  no  tendency  to  recover  when  stress  is 
removed;  and  hence  the  whole  weight  would  be  removed 
instantaneously,  and  the  curve  representing  the  removal  of 
weight  with  time  would  simply  consist  of  the  two  straight 
lines  at  right  angles,  ^  =  0  and  W=500.  I£  we  suppose  that 
all  the  curves  do  break  when  they  meet  this  dotted  curve,, 
then  it  is  obvious  from  the  diagram  that  the  breaking  point 
of  the  4*5  per  cent,  curve  must  be  at  a  considerably  greater 
time  and  a  considerably  less  weight  than  that  of  the  4*4  per 
cent,  curve.     This  supposition  is  to  some  extent  justified  by 
