100 



Professor H. L. Callendar 



[March 10, 



third power law at high temperatures, and would not be admitted aa 

 probable, at least by physicists, at the present time. 



The various formulae above mentioned, together with the methods 

 employed and the results deduced, are summarised in the following 

 table : — 



Table I. — Law op Kadiation. 



Observers and date. 



Dulong and Petit/ 

 (1817) \ 



Kosetti (1878) ..{ 



Stefan (1878) 

 Schleiermacher / 

 (1885) \ 



Weber (1888) 



Bottomley(1888)..| 



Paschen (1893) ..{ 



Wilson and Gray/ 

 (1897) \ 



Petavel (1898) ..{ 



Temperature 

 measured by 



Radiation 

 observed by 



Mercury 

 thermometer 



Mercury 

 thermometer 



Rate of cool-1 



ing in vac. J 



Thermopile \ 



Sb-Bi J 



No experiments made. 



Platinum Heat loss "I 



resistance | C 2 R in vac. J 



No experiments made. 



Heat loss "I 

 C 2 R in vac. / 



Bolometer 



Radio- ) 

 micrometer J 



Bolometer 



Formula 

 proposed. 



E, 1-0077? 



E 3 T 3 (nearly) 

 E 4 T 4 

 E 4 T 4 



E 2 T1-00043t 

 E 6 T 5 - 7 * 



E 6 T 5 - 7 * 



E 4 T 4 



E,T S * 



Solar ti-nip, 

 deduced. 



°C. 

 1900 



12,700 

 6900 

 6900 

 2450 

 4000 



4000 



6900 



4800 



* Formulas deduced by the writer from the observations. 



The foregoing table is not intended to be exhaustive, but merely 

 as a comparison of typical formulae, reduced to a common standard. 

 It does not contain the results of photometric investigations. 



The conclusion to be derived from the above illustrations appears 

 to be, that in order to arrive at any certain knowledge with regard to 

 the law of radiation, and the measurement of such extreme tempera- 

 tures as those of the arc, and of tho sun, the first step must be to 

 secure a higher order of accuracy in the determination of the highest 

 temperatures which can be observed and measured in the laboratory 

 with material thermometers. There are other difficulties which are 

 peculiar to the determination of the law of radiation, but wo are at 

 present concerned primarily with those relating to the measurement 

 of temperature. 



There are two comparatively independent lines along which 

 research may proceed with advantage at the present time: (1) The 

 direct comparison of different arbitrary methods ; (2) the extension of 

 the range of the gas-thermometer. 



In order to secure consistency of statement and the reduction of the 

 results of different observers to a common standard, it is in the first 

 place desirable that the various methods available at the present time 

 for the measurement of high temperatures in the laboratory should be 

 directly compared inter se, through the greatest possible range. It is 



