RADIATION IN ABSOLUTE MEASURE. 
443 
indicated on the diagram by the dots surrounded by dotted circles. It will be seen 
that, so far as they have gone, my experiments give no confirmation to this supposed 
law; and the results of Herr Schleiermacher lead to a precisely similar conclusion. 
Comparing the results of Schleiermacher with my own, I find a satisfactory 
agreement between them. His results, except for what is termed, in connection with 
Stefan’s Law, “ the radiation constant,are not stated in absolute measure;! but the 
particulars given in his paper enable me to calculate the loss, in heat-units lost per 
square centimetre per second. Schleiermacher used in his experiments three wires 
—two of bright polished platinum, and one of platinum coated with black oxide of 
copper. These are called respectively Pt 1 , Pt 3 , and Pt 3 . 
The following Tables, and the corresponding curves, Plate 26, show the results 
of Schleiermacher reduced to absolute measure. The column headed t gives the 
temperature Centigrade of the radiation wire ; that headed CHt/Js is the loss of 
heat in gramme-water-degree units per square centimetre per second; while the 
column headed Em is the emissivity, and is found by dividing the absolute loss by 
the difference of temperatures of radiation wire and surroundings. The temperature 
of the water surrounding the envelope, which was of glass, was in each case quoted 
0° C. Along with these results I give for comparison a similarly calculated set of 
results from one of my own series. 
Ptq, No. 1. (Enclosure at 0° C.) 
t 
C 2 R/Js 
Em 
o 
180 
28-08 x 10 4 
2L-6 x 10- 6 
200 
60-0 
30-0 „ 
337 
181-1 
53-8 „ 
581 
793 
137 
826 
2600 
315 
Pt 2 , No. 1. (Enclosure at 0 C C.) 
t 
C 2 R/Js 
Em 
O 
65 
9-45 x 10~ 4 
14-5 x 10- G 
no 
20-53 „ 
18-7 „ 
232 
74-7 
32-2 „ 
383 
236 
61-6 „ 
740 
1468 
198 
900 
3218 
358 ,, 
* The radiation constant is C 2 R/Js (T 4 — T 0 4 ). 
t It is surprising to find the paucity o£ the experimental results as to emission of heat which are 
stated in absolute measure ; so that, although we have many comparisons between surfaces of lampblack, 
black paper, white paper, oxidised metal, polished metal, &c., there is scarcely a trustworthy result to be 
