USEFUL PROJECTS. 
periments for surrounding or cover- 
ing the bulb of the thermometer, 
_ fluids excepted, had in a greater, or 
in a less degree, confined the heat, 
or prevented its passing into or out 
of the thermometer so rapidly as it 
would have done, had there been 
nothing but air in the glass globe, 
in the centre of which the bulb of 
the thermometer was. suspended. 
But the great question is, how, or 
in what manner, they produced this 
effect ? 
And, first, it was not in conse- 
quence of their own non-conducting 
powers, simply considered ; for if, 
instead of being only bad conductors 
of heat, we suppose them to have 
been totally impervious to heat, their 
volumes or, solid contents were so 
exceedingly small in proportion to 
the capacity of the globe in which 
they were placed, that, had they 
had_no effect whatever upon the 
air filling their interstices, that air 
would haye been sufficient to have 
conducted all the heat communi- 
cated, in less time than was actually 
taken up in the experiment. 
The diameter of the globe being 
1.6 inch, its contents amounted 
to 2.14466 cubie inches; and the 
contents of the bulb of the thermo- 
meter being only 0.08711 of a cu- 
bie inch (its diameter being 0.55 of 
an inch) the space between the bulb 
of the thermometer and the internal 
surface of the globe amounted to 
2.1440—60.087 11=2.05755 cubic 
inches; the whole of which space 
was occupied by the substances by 
which the bulb of the thermometer 
was surrounded in the experiments 
in question. 
. But though these substances oc- 
copied this space, they were far 
from filling it; by much the greater 
4 e722 
‘substances in question. 
409 
part of it being filled by the air 
which occupied the interstices of the 
In the ex- 
periment No. 4, this space was oc- 
cupied by 16 grains of raw silk ; and 
as the specific gravity of raw silk is 
to that of water as 1734 to 1000, 
the volume of this silk was equal to 
the volume of 9.4422 grains of wa- 
ter; and as one cubic. inch of water 
weighs 253,185 grains, its volume 
was equal to 7234325=0.037294 
of a cubic inch; and, as the space 
it. occupied amounted to 2.03755 
cubic inches, it appears that the silk 
filled no more than about =; part 
of the space in which it was con- 
fined, the rest of that space being 
filled with air. 
In the experiment No. 1, when 
the space between the bulb of the 
thermometer and the glass globe, 
in the centre of which it was con- 
fined, was filled with nothing but 
air, the time taken up by tbe ther- 
mometer in cooling from 70° to 10° 
was 576 seconds; but in the expe- 
riment No. 4, when this same space 
was filled with 54 parts air,and one 
part raw silk, the time of cooling 
was 1284 seconds. 
Now, supposing that the silk bad 
been totally incapable of conduct- 
ing any heat at all, if we suppose, 
at the same time, that it had no 
power to prevent the air remaining 
in the globe from conducting it, in 
that case its presence in the globe 
could only have prolonged the time 
of cooling in proportion to the quan- 
tity of air it had displaced to the 
quantity remaining ; that is to say, 
as 1 is to 54, or a little more than 
10. seconds. But the time of cool- 
ing was actually prolonged 708 se- 
conds (for in the experiment No. 1, 
it was 576 seconds, and io the ex- 
periment 
