RADIATION IN ABSOLUTE MEASURE AT VERY LOW TEMPERATURES. 375 
curves II. and III., it seems almost sure that the emissivity found would have been 
very close to that shown on curve I. 
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At the present time, Mr. King and I are endeavouring to make arrangements for 
carrying out experiments on the cooling of a sooted body, very much on the same 
lines as those on which we have been working, but with the cooling globe heated at 
the commencement to a temperature considerably above that of boiling water, and 
with the enclosure kept all the time at the temperature of liquid air. In our experi¬ 
ments up till now we have only been able to work, as it were, piecemeal and in 
sections; first, from the high temperature down to say 15° C., and then from 15° on 
to the lower temperature of liquid air. An experiment through the long range, and 
with the enclosure kept at the temperature of liquid air, would give data suitable for 
direct comparison with curve III. 
It may be, however, that after all a copper globe sooted is not a true “ black ” body, 
no matter how carefully prepared. One point, among others, on which there seems 
great uncertainty in this connection, is the question of conduction of heat from the 
surface of the copper to the sooty covering. This was a difficulty with the late Sir 
George Stokes, who discussed it with me on more than one occasion. 
I am preparing comparative experiments to test my sooted globe against the 
artificial black body. 
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