Temperature of the Carbons of the Electric Arc, Sfc. 25 



that pieces of its substance could be detached while the arc was 

 passing ; these white-hot pieces fell into a calorimeter, and from the 

 amount of heat given up, the temperature was calculated, assuming 

 the specific heat of carbon at this point to have its theoretical 

 value. The method does not seem at first sight a very reliab 1 .) 

 one, and Violle states that the result is only to be regarded as an 

 approximation. 



The method adopted by the authors of this paper is exactly the 

 same as that which they employed last year in their " Experimental 

 Investigations on the Effective Temperature of the Sun,"* in the 

 account of which full descriptions of the apparatus used, &c., are 

 given. 



A Brockie-Pell arc lamp was employed in the experiments, the 

 current being obtained from a dynamo worked by a gas engine. It 

 would have been preferable for some reasons to have worked the arc 

 off the 26 Epstein accumulators which we had at our disposal, but 

 the current from these was used in heating the platinum strip, and we 

 did not wish to run the cells off too quickly. Platinoid resistances 

 were inserted in circuit with the arc until it burnt steadily. 



The general arrangement of the apparatus is shown diagram- 

 matically in Fig. 1. 



FIG. 1. 



J 



JR. 



P is the platinum-strip radiator (our modification of Joly's meldo- 

 meter), the dotted line representing the water-jacket which is placed 

 over the strip. B, is the radio -micrometer ; A and B are tubes 

 through which radiation can pass to fall on the receiving surfaces 

 within. The diameter of the aperture at A is accurately known ; as 

 also is its distance from the receiving-surface, so that the apparent 

 area of platinum, as seen from the latter, may be calculated. 



L is the lamp, which is placed inside a wooden box, lined internally 

 with tin-plate, both wood and metal being pierced with small holes 

 opposite to the arc. 



A screen, S, hangs in front of the box, and contains a small, 

 carefully-measured hole, which can be adjusted until the brightest 

 (or any) part of the glowing carbons shines directly into the tube B. 

 * Wilgon and Gray, ' Phil. Trans.,' A, vol. 185, 1894, p. 361. 



