304         Prof.  H.  A.  Bumstead  on  the  Heating  Effects 
This    was    obtained    by    suddenly    moving    the    controlling 
magnet  at  the  time  t  =  0 ;   it  represents  the  response  of  the 
Fig.  4. 
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suspension  to  a  sudden  impulse.  The  following  values  for 
7  for  zinc  and  lead  were  obtained  from  the  cooling  portions 
of  these  curves  : 
Zinc. 
dV. 
V 
dt 
y. 
2-0 
1-2 
0-6 
10 
058 
0-58 
05 
0-38 
0-76 
Average    
0-65 
V. 
10 
0-5 
0-3 
Lead, 
dV 
dt 
lo 
0-8 
0-48 
Average 
1-5 
1-6 
1-6 
1-G 
Later  in  the  course  of  the  experiments,  the  aluminium 
widow  was  replaced  by  a  glass  one  and  the  strips  heated  by 
means  of  a  beam  of  light  ;  the  result  of  such  an  experiment 
