RADIANT HEAT, AND ITS CONVERSION THEREBY INTO SOUND. 
325 
Long experimental tube. 
Pressure. Absorption. 
1 inch.22*3 per cent. 
2 inches.29*5 „ 
Short experimental tube. 
Pressure. Absorption. 
3*5 inches .... 22*5 per cent. 
7*0 .... 30-0 
The agreement here is almost as close as that established by the first experiment. 
With a still brighter source of heat the absorptions were :—- 
Long tube. 
1 inch.18'4 per cent. 
2 inches.25*7 „ 
Short tube. 
3*5 inches 
7*0 „ 
18*8 per cent. 
25*6 
>5 
When, therefore, the density of the vapour varies inversely as the length of it 
traversed by the calorific rays, the absorption remains constant. 
The hydride of amyl lends itself conveniently to experiments of this character. 
With it, and with the lime light as source, the following measurements have been 
made :— 
Hydride of amyl. 
Long experimental tube. 
Pressure. Deflection. 
1 inch .... 10° 
2 inches ... 15° 
Total heat 49*4° 
Absorption. 
12*8 
19*2 
Short experimental tube. 
Pressure. Deflection. Absorption. 
3*5 inches . . . 10° 12*2 
7*0 „ . . . 15° 18*3 
Total heat 50*5° 
