EADIATION or HEAT BY OASEOBS MATTEE. 
93 
the. gas to be examined into contact with the source. I obtained thus an action forty 
times what I knew it ought to be, and was confirmed in the view which caused me to 
interpose a vacuous chamber in front of the experimental tube. Let me here record a 
few experiments made on the 4th of last November in connexion with this subject. 
I first satisfied myself that the drying apparatus was in perfect condition, the air of 
the laboratory producing, when sent through it, an absorption of 1. This same air was 
sent into the front chamber, that is, into direct contact with the source. The galvano- 
meter needle moved as it does in the case of absorbent gases, and at the end of two 
minutes declared .a loss of heat equivalent to an absorption of 50. The front chamber 
is 8 inches in length; the experimental tube is 33 inches long; hence a column of 
8 inches, in contact with the radiating surface, produced at least fifty times the effect of 
a column more than four times as long when the air was separated from the radiating 
surface. 
I made the foregoing experiment three times in succession, and after two minutes 
found the needle pointing to precisely the same degree ; the lowering of the source was 
perfectly constant and regular, and in all cases showed a loss equivalent to an absorp- 
tion of 50. 
It will be remembered that Professor Magxus obtained a greater absorption with 
hydrogen than with either oxygen or air. This result is perfectly explained by refer- 
ence to the quicker convection of this gas. I operated with hydrogen as I did with air, 
first satisfying myself that a column of it 33 inches long exercised an absorption less 
than unity. In fact it could not be measured. The same hydrogen introduced into the 
first chamber, and allowed to remain there for two minutes, caused a withdrawal of heat 
from the source equivalent to an absorption of 
65. 
Now the absorption of air in Professor Magnus’s experiments is to that of hydrogen as 
11-12 : 14-21, 
or as 50 : 64, 
while my results of convection are as 50 : 65. 
The coincidence is so perfect that I am disposed to regard it as in part accidental. 
Substantially the same remarks apply to the experiments with the glass tube stopped 
with plates of glass 4 millimetres thick. According to Melloni, 61 per cent, of the rays 
of a Locatelli lamp are absorbed by a plate of glass only 2-6 millimetres thick. Pro- 
fessor Magnus surrounded his flame by a glass cylinder, and this, it may be urged, par- 
tially sifted the heat of the lamp before it reached the end of the tube. But in so doing 
the glass cylinder itself must become intensely heated, and to the heat of the cylinder 
the glass ends of the tube would be ojpake. They would absorb it all. Cold air admitted 
into such a tube is exactly similar to cold air let into my front chamber, it chills what 
is in part the source of heat, and maintains that chill by convection. The heat applied 
