Proceedings of the Royal Institution. 3© 



One-tenth of the heat of the canister at 32" may be called [' ^.2 '*^ 



•' Nine-tenths of the heat of the M-all reflected from the canister;^ V.^^^ocf 

 Hih may be called 64 X 0.9, or . . • • • (/-'r.i3Jj 6 



f,h J 



Total quantity of heat supplied by the canister in return for what 

 II iul^hidpts ........ 



IgO'*^' 



Suppose next, that the black side of the canister is presented to 

 the thermometer, ., , . 



}{j (The canister now radiates nine-tenths of its own heat at ^^l%:^uilM^ 



, then 32 X 0.9 is j ! 



'' It reflects one-tenth of the heat at 64* 6.4 



jt:i ^Total quantity of heat returned by the canister in exchange for 1 



. ., wliat it intercepts J35.2 



It will now be clearly seen, that the bright side of the canister 

 gives, by the double means of radiation and reflection, nearly twice 

 as much heat as does the black side, in return for what is equally in- 

 tercepted in either case. The bright side should therefore depress the 

 thermometer least, as it is found to do ; and thus are all the difl5- 

 culties of radiant heat and cold fully explained on the ingenious 

 and fortimate hypothesis of M. Prevost, requiring no frigorific prin- 

 ciple, nor any particular assumption concerning the nature or cause 

 of heat. It accounts for all the phenomena hitherto observed, and 

 relieves the mind from the unphilosophical idea of a separate prin- 

 ciple of cold ; an idea which is as painful and repulsive to the ima- 

 gination as the idea of a principle of darkness independent of light ; 

 yet the latter would almost be involved in the former, when it is 

 considered in how many and how various situations heat and light 

 are united, obeying the same laws, and exhibiting the same relations. 



j,3j^,,,,. , April 9th and I6th. 



^fj^o meetings took place on these evenings, in consequence of their 



occurring in Passion and Easter weeks. y 



April 2Sd. 

 ■ MTVrXtttlity, bn the flowing of Sand under Pressure. — The eflfects 

 ilIU8tra;ted this evening, by a variety of experiments, are those which 

 were obtained by M. Huber Burnand, when he was engaged in con- 

 strutting an anemometer. Our readers will find them already de- 

 scribed in the Journal at p. 396, vol. v. of tliis series, to which, and 

 to the original paper in the Bib. Univ., xl. 22, we will refer them. 



2C2 



