272 Dr. A. D. Denning on a Simple Method of 



in the figure by the dotted line, and which, before an 

 experiment, was evenly coated with a layer of lampblack 

 produced by the combustion of camphor. The space 

 between the cylindrical and hemispherical vessels was used 

 as a reservoir for steam or the other substances which were 

 employed to maintain the hemispherical radiator at the 

 temperature T,. The kibe B served as an inlet and the tube 

 C as an outlet for the steam ; the wider tube, D, was 

 subsequently added for the purpose of covering the hemi- 

 spherical radiator with ice. During the course of a series 

 of observations this part of the apparatus rested on the wooden 

 board, W. (The stands supporting this latter are not shown in 

 the diagram.) 



As mentioned above, the elements of the thermo-junctions 

 were silver and constantan. In order to have an appreciably 

 large surface to receive the radiation at the one junction, the 

 silver and constantan wires were soldered on to a silver disk, 

 JW. This disk, after having been thoroughly well polished, 

 was mounted in a vulcanite frame, FGr, which fitted into 

 the wooden board carrying A. The disk also was lamp- 

 blacked before being used. If it be considered desirable to 

 prevent the disk receiving radiation at the sides, felt or some 

 other non-conducting material might be so wrapped round 

 the disk that only the top surface of it was exposed to the 

 hemispherical radiator. The Avires coining from the disk 

 were led down the arm GH to the binding-screws at the 

 bottom. The other junction of the thermo-couple was placed, 

 together with a thermometer, T, in a test-tube containing oil 

 in the glass beaker, K. The two constantan wires were 

 further soldered to copper wires leading through a mercury 

 commutator to the galvanometer. These last two (the 

 Cu-constantan) junctions were passed through rubber tubing- 

 fitting into two holes in the lid of a tin canister packed with 

 cotton-wool. 



The dimensions of the silver disk were : 



Diameter = 2'015 cm. Weight = 8*911 gr. 

 Thickness = 0*275 cm. Sp. Ht. =00567. 



This value for the specific heat was the mean of several 

 determinations made by means of a Joly steam calorimeter. 



Inasmuch as the source of steam and also the outlet from 

 the vessel A were on the side CD of the apparatus, a long- 

 piece of sheet nickel, polished on the one side, w r as tacked on 

 to the wooden stand W, with the idea of screening the 

 underside of the silver disk from the hot air currents. It 

 was also found advisable to further protect the disk from 



