C 179 J 
XI. An Inquiry concerning the Weight ascribed to Heat. By 
Benjamin Count of Rumford, F. R. S. M. R. I. A. &c. 
Read May 2, 1799. 
The various experiments which have hitherto been made 
with a view to determine the question so long agitated, re- 
lative to the weight which has been supposed to be gained, or 
to be lost, by bodies upon their being heated, are of a nature 
so very delicate, and are liable to so many errors, not only on 
account of the imperfections of the instruments made use of, 
but also, of those, much more difficult to appreciate, arising from 
the vertical currents in the atmosphere, caused by the hot or 
the cold body which is placed in the balance, that it is not at 
all surprising that opinions have been so much divided, relative 
to a fact so very difficult to ascertain. 
It is a considerable time since I first began to meditate on 
this subject, and 1 have made many experiments with a view to 
its investigation ; and in these experiments, I have taken all 
those precautions to avoid errors, which a knowledge of the 
various sources of them, and an earnest desire to determine a 
fact which I conceived to be of importance to be known, could 
inspire ; but, though all my researches tended to convince me 
more and more, that a body acquires no additional weight upon 
being heated , or rather, that heat has no effect whatever upon 
the weights of bodies, I have been so sensible of the delicacy of 
