108 PHILOSOPHICAL TRANSACTIONS. [aNNO 1786. 



diluted spirit of nitre, that when highly rectified spirit of wine, such as N° 8, is 

 diluted with 1-^ its weight of water, its point of aqueous congelation will be at 

 — 21°. The congealed part of the spirit was white like diluted milk, and even 

 the decanted part, which was full of thin films of ice, had a milky hue. The 

 fluid part was stronger than the rest, and no increase of cold was pro- 

 duced by adding snow to some of it, both of which are marks of aqueous con- ■ 

 gelation. 



The natural cold, when these experiments were made, is remarkable; as 

 there were at least Q mornings in which the cold was not less than that of freez- 

 ing mercury ; 4 in which it was at least 8° below that point, or — 47° ; and 1 in 

 which it was — - 50°. Whereas out of Q winters, during which Mr. Hutchins 

 observed the thermometer at Albany Fort, there were only 12 days in which the 

 cold was equal to that of freezing mercury, and the greatest cold seems to have 

 been — 45°. I cannot learn whether the last winter was more severe than usual 

 at Hudson's Bay ; or whether Henley-House is a colder situation than Albany, 

 which may perhaps be the case ; for though it is only 130 miles distant from it, 

 yet it stands inland, and to the w. or s. w. of it, which is the quarter from which 

 the coldest winds blow. 



XIF. New Experiments on Heat. By Col. Sir B. Thompson, Knt. F. R. S. 



p. 273. 



Examining the conducting power of air, and of various other fluid and solid 

 bodies, with regard to heat, I was led to examine the conducting power of the 

 Torricellian vacuum. From the striking analogy between the electric fluid and 

 heat respecting their conductors and non-conductors (having found that bodies, 

 in general, which are conductors of the electric fluid, arQ likewise good conduc- 

 tors of heat, and, on the contrary, that electric bodies, or such as are bad con- 

 ductors of the electric fluid, are likewise bad conductors of heat,) I was led to 

 imagine that the Torricellian vacuum, which is known to afford so ready a pas- 

 sage to the electric fluid, would also have afforded a ready passage to heat. The 

 common experiments of heating and cooling bodies under the receiver of an air- 

 pump I concluded inadequate to determining this question ; not only on account 

 of the impossibility of making a perfect void of air by means of the pump ; but 

 also on account of the moist vapour which, exhaling from the wet leather and 

 the oil used 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 recourse therefore to other contrivances. 



I took a thermometer tube, the diameter of whose globular bulb was just half 

 an inch, Paris measure, and fixed it in the centre of a hollow glass ball of the 

 diameter of 1 -|- Paris inch, in such a manner, that the short neck or opening of 



