Experiments upon Heat. 6*3 
That thread wound light round the bulb of the thermometer 
should form a covering less warm than the same quantity of 
wool, or other raw materials of which the thread is made, sur- 
rounding the bulb of the thermometer in a more loose manner, 
and consequently occupying a greater space, is no more than 
what I expected, from the idea I had formed of the causes of 
the warmth of covering ; but I confess I w’as much surprised 
to find that there is so great a difference in the relative 
warmth of these two coverings, when they are employed to 
confine great degrees of heat, and when the heat they confine 
is much less in proportion to the temperature of the surround- 
ing medium. This difference was very remarkable ; in the 
experiments with sheep’s wool, and with woollen thread, the 
W’armth of the covering formed of 16 grains of the former, 
was to that formed of 16 grains of the latter, when the bulb of 
the thermometer was heated to 70° and cooled to 6o°, as 79 to 4 6 
(the surrounding medium being at o 4 ) ; but afterwards, when 
the thermometer had only fallen from 20° to io° of heat, the 
warmth of the wool was to that of the woollen thread only as 
426 to 410 ; and in the experiments with lint, and with linen 
thread, when the heat was much abated, the covering of the 
thread appeared to be even warmer than that of the lint, 
though in the beginning of the experiments, when the heat 
was much greater, the lint was warmer than the thread, in the 
proportion of 80 to 46. 
From hence it should seem that a covering may, under cer- 
tain circumstances, be very good for confining small degrees of 
warmth, which would be but very indifferent when made use 
of for confining a more intense heat, and vice versa. This, I 
believe, is a new fact ; and, I think the knowledge of it may 
