508 On (he Radiation of Cold. 



Acrts. 



Brought forward 433,090 



Rother (upper parts) 43,000 



Schoo 1 0,000 



Sence (in Ravenstone) 2,000 



Sheaf (upper part) 5,000 



Shelf 10,000 



Trent (middle parts) 70,000 



Wye 45,000 



Total of Derbyshire 629,080 



[In my next I intend to follow up thjs subject, by extractino- Mr. Farcy's 

 account of tlie more rocky and prrcipitous I'uLUys, &c. — Editor.] 



XXIX. On the Radiation of Cold. By a Correspondent. 



To Mr. Tilloch. 



Sir, XlAviNG lately seen repeated at the Royal Institution, 

 the experiment of the supposed radiation of cold ; and be- 

 ing dissatisfied with the explanations commonly offered of 

 this phaenonienon, I am induced to trouble yon with this 

 cointnunication, in order to learn uhether an explanation 

 which I have to (jffcr, may appear to others more satistaclory 

 than any of th(^se usually given. 



The experiment is too familiar to men of science to need 

 description ; I will just mention the explanation usually 

 given, as I draw my conclusion from precisely the same 

 premises, without attempting any new experiments. 



Mr. Daw stated that heat constantly radiated from all 

 bodies ; and as the temperature of the thermometer placed 

 in the focus nf the one nurror is maintained by such radia- 

 tion, if a piece of ice be placed in the focus of the other 

 mirror, it displaces a portion of air which bcfoie assisted 

 by its radiation (for he said that air did radiate heat) in niain- 

 taininiT that temperature : the thermometer therelore falls, 

 but the ice being removed it again rises. Were this ex- 

 planation the. true one, it would follow, that when the ther- 

 mometer is placed in the focus of the one mirror, although 

 there be nothing but air in the oppositt; one, it ought to 

 rise; otherwise U could not be depi<s>eil by the abstraction 

 of that air, anv mure than by that of an equal quantity in 

 anv other spot at an equal distanec. 



but if it be true, that all bodies do constantly radiate 



heat. 



