426 
Substituting these values we find 
Roe (5 ne 1) LOOT, a} mm 
C be c Xu 
The units being gramme, metre, second, centigrade. 
The experimental value of z for aluminium has not He 
found, but Prof. Maxwell has pointed out to me that Edlund 
has determined it for some other metals. So, though we are 
unable to calculate the amount of the heating for an aluminium 
disk, we may get an idea of its magnitude by taking some other 
metal. If we take silver we shall have 
© =1-0203, 
Cc 
e= 057,45 
yw = 000057, 
X= 8481 x 10° grammes per square metre, 
m =10'4 x mass of cubic metre of water, 
=10°4 x 10° grammes. 
Substituting these we find for a silver disk under the con- 
ditions of the experiment, 
Fall of temperature on expanding = 4° C. 
As the conductivity of silver is very high, the heat absorbed 
during rotation would be rapidly conducted inwards, and there- 
fore after 40” the disk will almost have risen to the surround- 
ing temperature, and consequently on stopping the disk we 
should get the whole effect of -4°C. showing itself. If we 
take into consideration the effect of the conduction at the end 
of 40”, the surface would be -04° C. below the surrounding space, 
and therefore on stopping the disk the temperature observed 
ought to be 36°C. ; 
The order of magnitude of the effect is thus the same as 
