492 Mr. Cavendish’s Experiments to determine 
any sensible effect, and though it seemed improbable that, in 
all the foregoing experiments, the weights should happen to be 
warmer than the case, I resolved to examine into it, and for 
this purpose removed the apparatus used in the last experi- 
ments, and supported the weights by the copper rods, as before ; 
and, having placed them in the midway position, I put a lamp 
under each, and placed a thermometer with its ball close to 
the outside of the case, near that part which one of the weights 
approached to in its positive position, and in such manner 
that I could distinguish the divisions by the telescope. Having 
done this, I shut the door, and some time after moved the 
Weights to the positive position. At first, the arm was drawn 
aside only in its usual manner; but, in half an hour, the effect 
was so much increased, that the arm was drawn 14 divisions 
aside, instead of about three, as it would otherwise have been, and 
the thermometer was raised near i°i; namely, from 6i°to 6 2°i 
On ^opening the door, the weights were found to be no more 
heated, than just to prevent their feeling cool to my fingers. 
As the effect of a difference of temperature appeared to be so 
great, I bored a small hole in one of the weights, about three- 
quarters of an inch deep, and inserted the ball of a small 
thermometer, and then covered up the opening with cement. 
Another small thermometer was placed with its ball close to 
the case, and as near to that part to which the weight was ap- 
proached as could be done with safety; the thermometers 
being so placed, that when the weights were in the negative 
position, both could be seen through one of the telescopes, by 
means of light reflected from a concave mirror. 
