274 &V Benjamin Thompson’s 
Examining the conducing power of air, and of various 
other fluid and folid bodies, with regard to heat, I was led to 
examine the conducting power of the 'Torricellian vacuum . 
From the finking analogy between the eleCtric fluid and heat 
refpeCting their conductors and non-conduCtors (having found 
that bodies, in general, which are conductors of the electric 
fluid, are likewife good conductors of heat, and, on the con- 
trary, that eleCtric bodies, or fuch as are bad conductors of the 
eleCtric fluid, are likewife bad conductors of heat), I was led to 
imagine that the Torricellian vacuum, which is known to 
afford fo ready a paffage to the eleCtric fluid, would alfo have 
afforded a ready paflage to heat. 
The common experiments of heating and cooling bodies 
under the receiver of an air-pump I concluded inadequate to 
determining this queftion ; not only on account of the impof- 
fibility of making a perfeCt void of air by means of the pump ; 
but alfo on account of the moift vapour, which exhaling from 
the wet leather and the oil ufed in the machine, expands under 
the receiver, and fills it with a watery fluid, which, though 
extremely rare, is yet capable of conducting a great deal of 
heat : I had recourfe therefore to other contrivances. 
I took a thermometer, unfilled, the diameter of whofe 
bulb (which was globular) was juft half an inch, Paris 
meafure, and fixed it in the center of a hollow glafs ball of 
the diameter of i J Paris inch, in fuch a manner, that the 
ftiort neck or opening of the ball being foldered faft to the tube 
of the thermometer yi lines above its bulb, the bulb of the 
thermometer remained fixed in the center of the ball, and 
confequently was cut off from all communication with the 
external air. In the bottom of the glafs ball was fixed a fmall 
hollow tube or point, which projecting outwards was foldered 
to 
