236 



Apparent Radiation of Cold. 



Art. XXII. On the Apparent Radiation op Cold. By 

 Benjamin F. Joslin, M. D. Prof. Math. Union College. Cor- 

 responding Member. 



In a well known experiment with two concave specula, a calorific 

 principle is evidently radiated and reflected, and moves in right 

 lines with great velocity. The celebrated Florentine experiments, 

 a modification of the former, seems at first sight to establish no 

 less conclusively the radiation of a frigorific principle, which ob- 

 serves the same laws as radiant heat. " It becomes therefore a 



explanation of this phenomenon, which shall accord with the dLtrine 

 that cold is simply the negation of heat." M. Prevost has, in my 

 opinion given a satisfactory solution of this interesting problem, in 

 his'highly ingenious yet simple theory. With this distinguished 

 philosopher the idea originated, that a mutual participation of radi- 

 ant caloric takes place between bodies at all temperatures, and that 

 a warm body has its temperature reduced by a cold one in its vici- 

 nity, merely in consequence of receiving only a partial compensa- 

 tion for the rays it has emitted. This hypothesis, however, has 

 not been universally adopted. It has been rejected by many phi- 

 losophers, and among others, by the late celebrated Dr. Murray, 

 and by the authcr of the article on " Cold," in that valuable sci- 

 entific work, the New Edinburgh Encyclopaedia. The latter re- 

 marks, that " this explanation, depending upon the assumed prin- 

 ciple that bodies at all temperatures radiate caloric, in a degree 

 proportional to the quantity of that power which they contain, is to- 



of bodies. ForlfTt^ p^X^nT^ 

 perature takes place between the hotter and the colder body, until 



even goes on after an equilibrium is established between thenjit 

 is evident that a hot body ought to cool more slowly when it is pla- 

 ced near a large body of inferior temperature, than near a small 

 one. But the fact is precisely the reverse." 



nau? 6 * n8Wer t0 thiS ^ °f ViOUS ' ^ mtensit7 ° f ° alorific ema ~ 

 is inversely as the distance from the point whence ZPem^nZd; 

 whdst two surfaces of a similar figure, being placed at different 

 distances irom a thermometer, and subtending equal angles at it, 



