CATALOGUE. — HEAT, llADIATIOK, 



407 



Found that a blackened wire was sooner heated and cooled 

 than a wire not coloured. 



Huttons dissertation on light, heat and fire. 8. 

 Ace. Ed. tr. IV. H. 7. Read 1794. 



Calls radiant heat obscure light ; observes the greater heat 

 of the red rays, and says that a blackened thermometer is 

 most sensible to the eflTect of obscure light, as well as to 

 that of visible light. 



*Herschel on the heat of the prismatic rays, 

 on the invisible rays of the sun, and on 

 the solar and terrestrial rays that occasion 

 heat. Pli. tr. 1800. <-l55, 284, 293,437. 

 Nich. IV. 320, 360. V. 69. Ph. M. VII. 

 VIII. Giib. VII. 137. 



With many experiments on the transmission of heat. 



fLeshe's observations on hght and heat. 



Nich. IV. 344, 4l6. Giib. X. 88. 

 *Leslie on heat. 



Benzenberg's remarks on Leslie. Giib. X. 

 ' '350. 

 Hermst'adt on the effect of heat on different 



colours. A. Berl. 1801. 83. 

 ^chraidtniliiler on the heat communicated 



to wood by the sun's rays. Giib. XIV. 



30G. 

 Kumford's experiments on radiant heat. Ph. 



tr. 1804. 77. B. Soc. Phil. n. 87. Giib. 



XVII. Sti, 218. 



On the effects of colours, and on the nature of the 

 surface. 



Bockmann's prize essay on the heating of 

 bodies in the solar rays. Note. Giib. XVII, 

 122. 



On the velocity of radiant heat. Ph. M. 

 XIX. 309. 



Parker's was a double convex lens, three feet in diameter, 

 3 inches thick in the middle : it weighed 212 pounds. Its 

 aperture when set was 32j inches ; its focal length fl feet 

 8 inches : the focal length was generally shortened by a 

 smaller lens. The most refractory substance fused was a 

 cornelian, which required 75" for its fusion; a crystal 

 pebble was fused in a" ; a piece of white agate in 30". 

 Cavallo. The finger might be pUced in the cone of rays 



within an inch of the focus, without inconvenience. 

 Imison's elements. I. 371. But tins remark appears to 

 require confirmation : if it were accurate, we might expect 

 the smallest imperfection in the focal adjustment of the eye 

 to cause a great difference in tlie apparent brilliancy of an 

 object ; which is not the fact : indeed Count Rumford's 

 late experiments appear wlioUy to confute it. 



Leslie discovered, by experiments made in 1802, that the 

 heat emitted by radiation was affected by the natme of ths 

 surface exposed. The action of a blackened surface of 

 tin being 100, that of a steel plate was 15, of clean tin 12, 

 of tin scraped bright 16, when scraped with the edge of a 

 fine file in one direction 26, when scraped again across 

 about 13, a surface of lead clean 19, covered with a grey 

 crust 45, a thin coat of isinglass 80, resin 96, writing paper 

 98, ice 85. Heat as well as light is so projected from a 

 surface as to be equally dense in all directions, consequently 

 from each point in a quantity which is as the sine of the 

 angle of inclination. The radiation is not affected by the 

 quality of the gas, in contact with the surface, but it is not 

 transmitted by water. For the time of cooling of a hol- 

 low tin ball 6 inches in diameter, filled with water, in 



still air, take, in minutes, L.— — L. , making the 



t a -^ I 



three first decimals integers, h and i being the tempera- 

 tures on the centigrade scale, and a being 50. And for 

 the same ball painted, make a z:: 110, and take ^^ of the 

 result: thus, from 100° C. to 50°, or 212° F. to 122°, 

 metal takes 124'.9, paper or paint 83'.2, to 10° C. or 50° 

 F. 602' and 344'. 1 respectively. For the effect of diffiirent 

 gases and different densities, in air the discharge from a 



vitreous surface is -5(3^^ + ■*(i^''), from a metallic surface 



i J Jt 1 



^(3 <;•' + f(2") ; in hydrogen gas Kisd* 4- id'^^), and 



^(12J' + Jd"). Thus, if d r: 1, theabductive power of 

 air is |, or .4286, tlie pulsatory energy of a vitreous surface 

 i, or .5714, of a metallic surface ,L, or .0714. In hydrogen 

 gas the pulsatory power the same, the abductive power 

 '-?, or 1.7143. If cir:-5^, the abductive power is .18 for air, 

 .857 for hydrogen, the pulsatory power .48 or .06 in air, 

 .51 or .0637 in hydrogen. If d :=^^!^, the abductive 

 power is .1071 for air, .5655 for hydrogen, the pulsatory- 

 power .433 or .054 for air, .475 or .0594 for hydrogen. 

 It would be easy to make an experiment on the velocity 

 with which radiant heat is conveyed to a distance, and 

 there is little doubt but that such an experiment would 

 confute Mr. Leslie's hypothesis of the transmission of heat 

 by a pulsation of the air propagated with the velocity of 

 sound. 



