771 



PHILOSOPHICAL TRANSACTIONS. 



[ANNO 1800. 



Min. Black paper. Black satin scattering. 



Exper. 210. 76'i - 76\ Black satin scatters 1409 rays of 



5 79 80-L . . . 2f : 5} = 1.409- heat, and 243 of light. 



Ex/er. 211. — Having now ascertained, that of all the white and black substances I had tried, white 

 muslin scatters the least, and black satin the most Min. White muslin. Black satin scattering, 

 heat, I placed the former on one tablet, while the 764 76% 



latter was put on the other. 5 80 80£ . . . 34, : 3£ = 1 .069. 



Here the black object scattered more heat than the white one ; but, in order to try again the equality 

 of the tablets and apparatus, I placed the objects Min. Black satin. White muslin scattering, 

 under the opposite thermometers, and had as 78 78 



annexed. 5 80*- 80| . . . 24, : 2 J = 1.050. 



So that, notwithstanding some little difference in the apparatus, or other unavoidable circumstances, 

 the black object gave again the greatest scattering of heat ; and consequently as no colour can be more 

 opposite than black and white, colour can have no concern in the laws that relate to the scattering 

 of heat. 



Exper. 212. — I wished now to try some expe- Min. Iron, 



riments of the scattering power of metals, and 74 



had some plates of iron, brass, and copper, 2 5 78| 



inches square, set flat, and smooth-filed, by round strokes. 



Min. Tin foil. Gold-leaf paper scattering. 



Exper. 213. 74 74 But the tin foil was considerably 



5 77 J 79$ ••• 3f : &f = l - 500 - tarnished. 



Exper. 214. — Binding the form of the last ex- Min. White paper. Tin foil scattering. 



Copper scattering. 

 733 

 77\... 4$: 4* = .917. 



50{ 

 534 



52 



541. 



3| : ftg = .885 



periments inconvenient, for want of a standard, 

 I had recourse again to white paper. 5 



This substance scatters 885 rays of heat, and 8483 of light. 



Min. White paper. Iron. 



Exper. 215. 51f ( 53| 



5 544, 55| . . . 3 : 24 = .750. 



the present one, this plate of iron was not now so bright as before, and seems to have suffered 

 more than brass or copper from having been laid by : it scatters now only 750 rays of heat, and 10014 

 of light. 



Brass. 

 51| 



55% ... 3^ 

 Copper. 

 51} 



55J... 3^:4= 1.280. 

 Gold-leaf paper. 

 55% 



Min. 

 Exper. 216. 



Exper. 217- 



Exper. 2^8. 



White paper. 



50 



53| 

 White paper. 



m 



53 

 White paper. 

 54f 

 56£ 



4' = 1.320 



Some time having elapsed be- 

 tween the former observation and 



It scatters 1320 rays of heat, and 

 no less than 43858 of light. 



It scatters 1280 rays of heat, and 

 13128 of light. 



56 



1| 



« I changed the tablets to see what difference there 

 might be. 



I = .357. 



Gold paper. 

 55f 

 561 



White paper. 

 55£ 



572... 



\\ = .500 



A mean between the two gives .429- 

 less than 124371 rays of light. 



Min. Black velvet. 

 Exper. 219. 52 



5 53£ 



Gold paper therefore scatters only 429 rays of heat, and no 



Gold paper scattering. 

 51, 



5*f;. 



!£:£ = .556. 



I turned the tablets, in order to ascertain the 

 difference. 



Min. 

 

 5 



Gold paper, 

 51 

 51j 



Black velvet. 

 51| 

 53 ... I : l£ = .600. 



From a mean of both it appears, that when black velvet scatters 1000 rays of heat, and only 7 rays of 

 light, gold paper, on the contrary, scatters no more than 578 rays of heat, but 124371 of light. 



Art. 7. Whether Light and Heat be occasioned by the same, or by Different 

 Rays. — Before we enter into a discussion of this question, it appears to me that we 

 are authorised, by the experiments which have been delivered in this paper, to make 



