VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 57Q 



the heats of my own kilns and ovens, without being perceivable by the workmen 

 at the time, or till the ware was taken out of the kiln. 



p. s. Since the foregoing experiments were made, I have seen a curious Me- 

 moir by Messrs. Lavoisier and De la Place, containing a method of measuring 

 heat by the quantity of ice which the heated body is capable of liquefying. The 

 application of this important discovery, as an intermediate standard measure be- 

 tween Fahrenheit's thermometer and mine, could not escape me, and I imme- 

 diately set about preparing an apparatus, and making the experiments necessary 

 for that purpose; in hopes either of attaining by this method a greater degree of 

 accuracy than I could expect from any other means, or of having what I had 

 already done confirmed by a series of experiments on a different principle. But 

 in the prosecution of these experiments I have, to my great mortification, hitherto 

 failed of success; and I should have contented myself for the present with saying 

 little more than this, if some phenomena had not occurred, which appear not 

 unworthy of further investigation. 



The authors observe, that if ice, cooled to whatever degree below the freezing 

 point, be exposed to a warmer atmosphere, it will be brought up to the freezing 

 point through its whole mass before any part of its surface begins to liquefy; 

 and that consequently ice, beginning to melt on the surface, will be always ex- 

 actly of the same temperature, viz. at the freezing point; and that if a heated 

 body be inclosed in a hollow sphere of such ice, the whole of its heat will be 

 taken up in liquefying the ice; sd that if the ice be defended from external 

 warmth, by surrounding it with other ice in a separate vessel, the weight of the 

 water produced from it will be exactly proportional to the heat which the heated 

 body has lost; or, in other words, will be a true physical measure of the heat. 



For applying these principles in practice, they employ a tin vessel, divided, by 

 upright concentric partitions, into 3 compartments, one within another. The 

 innermost compartment is a wire cage, for receiving the heated body. The 2d, 

 surrounding this cage, is filled with pounded ice, to be melted by the heat; and 

 the outermost is filled also with pounded ice, to defend the former from the 

 warmth of the atmosphere. The first of these ice compartments terminates at 

 bottom in a stem like a funnel, through which the water is conveyed off; and 

 the other ice compartment terminates in a separate canal, for discharging the 

 water into which that ice is reduced. As soon as the heated body is dropped into 

 the cage, a cover is put on, which goes over both that and the first ice compart- 

 ment; which cover is itself a kind of shallow vessel, filled with pounded ice, 

 with holes in the bottom for permitting the water from this ice to pass into the 

 2d compartment, all the liquefaction that happens here, as well as there, being 

 the effect of the heated body only. Over the whole is placed another cover with 

 pounded ice, as a defence from external warmth. 



4 F. 2 



