ON THE NATURE OF HEAT. QQI 



The latter statement requires however some qualification The latter in 



and restriction; for 1 must now observe, that, allhoneh '''^"•^ ^.^^'^'f 

 _.,-., . 1 -J II 1 i/v • uuasmissible, 



iVlr. l-eslie s experiments prove decicledly the ditterence be- 



tvi'eeu solar and culinary heat in this respect, yet he has I 

 believe proceeded too fur, in asserting, that the latter is not 

 at ail transmissible through transparent media. That the 

 heat of a candle is in some degree refracted by glass is prc7«l 

 by the 13th experiment of Dr. J^erschel ; the heat of a com- 

 mon fire was transmitted and refracted in the 14th and l6th ; 

 the heat of redhot iron was refracted in the 15th; and invisi- 

 ble culinary heat was refracted in the 19th and 20th experi* 

 ments*. The heat emanating from a candle, from a boiling; 

 mixture of sulphuric acid and water, and from boiling wa- 

 ter, was transmitted through glass, in some experiments per- 

 formed by my friend Mr. Maycock f. 



The whole of these experiments concur in establishing a butnotequally 

 remarkable difference, between the transmission of radiant ^^ ^°^^^ ^^^^* 

 culinary and solar heat. Solar heat is scarcely if at all im- 

 peded, culinary heat almost entirely intercepted by transpa- 

 rent media I 



But this is not the only difference between solar and culi- Difference m 

 nary heat ; another distinction is observed in their reflection, 'h« reflection 

 «* Cover each ball of a differential thermometer with a coat culinarv^heau 

 ** of tinfoil, and rub that one below which the scale is af- 

 ** fixed gently with sand paper; or it may be rubbed before 

 " it is applied to the glass. Placing the instrument now in 

 *« the sun, the liquor will visibly rise, perhaps 5 or 10 de- 

 grees." *' Set this differential thermometer now directly 

 opposite the fire, and about two or three feet distant from 

 ** it. In this situation a very remarkable depression will 

 ** quickly take place, equal perhaps to 30 or 40 degrees.'* 

 ** This beautiful experiment likewise indicates clearly the 

 ** distinction between the solar rays and culinary fieat J.'* 



The explanation of this phenomenon, which follows its Attempt to ac- 

 relation, will not, I conceive be readily acquiesced in; '* the count for this* 

 * light from the fire, has," it is said, " some tendency, to 



<( 



i 



» Phil. Trans. 1800 j or Journal as above, 

 •; Phil. Journal, Vol. XXVl, p. 75. 

 Iloquirj, p. 8S> et t«^. 



•* counteract 



