276 Watson on the Heat produced by Friction. 
apparatus, the air would pass through the passage D e 
and be totally expelled; now turn the stop cock one quar- 
ter round and the communication between the air and the 
globe would be cut off, but that between the receiver and 
the globe through C would be opened, and as the 
mercury fell to its level, the air in the receiver would 
be rarefied ; restore the stop-cock to its original position, 
and the air in the globe might be again expelled by the mer- 
cury. Now suppose the receiver, by this method, to 
be exhausted of air; turn the stop-cock half round, 
and a communication is opened between the atmos- 
phere and the receiver. The requisite motions were 
to be communicated to the stop-cock by the same pow- 
er which was employed to work the pump, and methods 
of effecting this will readily suggest themse elves. I mention 
this matter not as claiming the credit of having proposed a 
construction of an air-pump, of the practical advantages of 
which I have great doubts, but simply as an improvement 
of that suggested by Mr. Patten. 
Art. XVII.—On the cause of the heat produced by Wee a 
by James .T. Watson. 
TO THE EDITOR. 
Dear Sir, 
] Have made some attempts to explain the cause of the 
heat excited by friction, an account of which | hope will 
be acceptable to you. 
In rubbing two bodies together it is evident that the air 
in their pores, and interstices will be compressed, and as 
air readily yields heat by pressure, it is possible that the 
heat excited by friction may be thus explained. 
If two subtances were rubbed together, and if at the 
same time, there could be similar friction in vacuo, by a 
comparison of the results an opinion might be formed of 
the effect of air with friction in exciting heat. I mentioned 
this explanation to Professor Renwick, and Dr. McNeven; 
they thought it probable, furnished air-pumps, and assisted 
in making experiments. 
A wooden spindle was fitted to a socket, and a similar 
spindle also fitted to a socket within the receiver of an air- 
