RADIATION IN ABSOLUTE MEASURE AT VERY LOW TEMPERATURES. 
359 
25. The emissivities in the present paper are calculated by two methods. To 
explain the working out of the results we cannot do better than quote two specimen 
pages out of the calculation note-books. These pages are not selected because they 
show any special feature; they are simply average specimens. 
Method 1. 
26. This method of calculating the emissivities is the one chiefly used in the former 
paper, ‘ Phil. Trans.,’ 1893. It is fully explained and illustrated there in an appendix, 
and a brief description of it here will suffice. Referring to p. 360 : Column 1 contains 
the times, against which the corresponding galvanometer deflections are noted in 
Column 2. These deflections correspond to the differences of temperatures between the 
thermojunctions,* and give the temperatures of the globe at those particular instants 
of time. Taking the common logarithms of Column 2, we get Column 3 ; and the 
difference between the successive logarithms of the deflections give us Column 4. 
To obtain the emissivities from the numbers in Column 4, they must be multiplied by 
(M x c) / (300 x S), the value of which is 3'868 x 10 -3 . This constant is smaller than 
that used in the 1893 paper on account of a reduction in the numerical value of c 
which it has been necessary to make for the diminished value of the heat capacity of 
the copper globes, owing to the low temperatures of the experiments.! 
27. The differences of the temperatures of the globe and its surroundings are read 
off from the thermojunction calibration curve already mentioned, § 14, and these are 
placed in Column 6 ; and Column 7 contains the arithmetic means of the successive 
pairs of these numbers. 
By adding the absolute temperature of the surrounding bath to the latter tempera¬ 
tures we get the absolute temperatures of the globe. These are placed in Column 8. 
Method 2. 
.28. In the second method the series of observations during any one experiment, 
lasting perhaps 2|- hours or more, are taken as a whole ; and the emissivities at various 
temperatures, from the highest to the lowest, are calculated as a continuous series ; the 
emissivity being supposed to alter continuously with the absolute temperature of the 
cooling body. 
For purposes of numerical calculation, however, the observed deflections, and the 
logarithms of these numbers, are, in this method, expressed as functions of the time 
reckoned from the beginning of the experiment in the way which is about to be 
* In Dr. Bottomley’s 1893 experiments it was necessary to apply certain corrections to the galvano¬ 
meter readings : (1) for the straight galvanometer scale used; and (2) a thermojunction correction. 
These were described among the details of calculation. They are not required here owing to our present 
improved arrangements. 
t U. Behn, ‘ Wiedemann’s Annalen,’ 66, 2, pp. 237-244 (1898); ‘ Annalen der Physik,’ 1, 2, 
pp. 257-269 (1900). Schmitz, ‘ Proc. Roy. Soc.,’ 72, pp. 177-193 (1903). 
