sS 
Sir Benjamin Thompson's 
differences in the warmth of these substances were much less 
than I expected to have found them. 
Suspecting that this might arise from the volumes or solid 
contents of the substances being different (though their weights 
were the same), arising from the difference of their specific gra- 
vities; and as it was not easy to determine the specific gra- 
vities of these substances with accuracy, in order to see how far 
any known difference in the volume or quantity of the same 
substance, confined always in the same space, would add to, or 
diminish, the time of cooling, or the apparent warmth of the 
covering, I made the three following experiments. 
In the first, the bulb of the thermometer was surrounded by 
16 grains of Eider down ; in the second by 32 grains ; and in 
the third by 64 grains ; and in all these experiments the sub- 
stance was made to occupy exactly the same space, viz. the 
whole internal capacity of the glass globe, in the centre of 
which the bulb of the thermometer was placed ; consequently 
the thickness of the covering of the thermometer remained the 
same, while its density was varied in proportion to the num- 
bers 1, 2, and 4. 
The results of these experiments were as follow : 
