101 
and the Mode of its Communication. 
the instrument in 30^ minutes, it appears that the velocity with 
which the heat was given off from the naked metallic surface, 
was to the velocity with which it was given off from the same 
surface covered with four coatings of spirit varnish, as 66 % to 
30^, or as 10000 to 4566. 
Without pursuing these computations any farther, at present, 
and without stopping to make any remarks on the curious facts 
they present to us, I shall hasten to experiments from the results 
of which we shall obtain more satisfactory information. But, 
before I proceed any farther, I must give an account of an in- 
strument I contrived for measuring, or rather for discovering , 
those very small changes of temperature in bodies, which are oc- 
casioned by the radiations of other neighbouring bodies, which 
happen to be at a higher, or at a lower temperature. 
This instrument, which I shall take the liberty to call a ther - 
moscope, is very simple in its construction. Like the hygrometer 
of Mr. Leslie, (as he has chosen to call his instrument,) it is 
composed of two glass balls, attached to the two ends of a bent 
glass tube; but the balls, instead of being near together, are 
placed at a considerable distance from each other ; and the tube 
which connects them, instead of being bent in its middle, and its 
two extremities turned upwards, is quite straight in the middle, 
and its two extremities, to which its two balls are attached, are 
turned perpendicularly upwards, so as to form each a right 
angle with the middle part of the tube, which remains in a hori- 
zontal position. 
At one of the elbows of this tube, there is inserted a short 
tube, of nearly the same diameter, by means of which, a very 
small quantity of spirit of wine, tinged of a red colour, is intro- 
duced into the instrument ; and, after this is done, the end of 
