upon Radiant Heat. 373 
Gold. Inclination, Yellow glass. Red glass. 
100: 70 100: 55 
Rough surface .........00 100: 66 100.51 
3 100: 71 100: 57 
Polished surface............ 100: 66 100 :50 
Unrefiected heat ......... 100 ; 65 100: 50 
We see here that the qualitative difference, in the case of heat 
reflected from a roughened surface of gold, disappears wholly 
when the rays fall upon the plate at a very small angle. 
Similar experiments were made with silver, mercury, copper 
and brass: the results are collected in the following Table :— 
Silver. Inclination. Yellow glass. Red glass. 
80 100:71 100 : 55 
Rough surface .........4.. 2 100: 65 100:51 
Polished surface ....,.... - ae a ae a 
Unreflected heat ......... 0 100 : 65 100: 50 
aes 80 100: 73 100 : 55 
Dull white surface......... 2 100: 69 100:51 
Shining metallic surface.. S ao a she 5 
Unreflected heat ....... 33 0 100 : 67 100: 51 
Copper. 
80 100: 73 100 : 53 
Rough surface ............ 2 100: 66 100: 48 
. 80 100: 73 100:53 
Polished surface,....0,..... 2 100 : 66 100: 48 
Unreflected heat ......... 0 100: 65 100 ; 48 
Sool 
wing 100: 70 100: 48 
Rough surface ............ 100: 66 100: 48 
3 100: 69 100: 48 
Polished surface............ 100: 64 100: 48 
Unreflected heat 100: 65 100; 48 
In all these cases the qualitative peculiarity which distinguishes 
