of Electricity from Hot Bodies 



307 



A. Wehnelt {Ann. d. Physik, vol. xiv. p. 3, 1904, and 

 Phil. Mag. vol. x. 1905) found that the negative leak from 

 hot platinum was very much increased on coating the metal 

 with a thin layer of calcium oxide or barium oxide *. 



In the following experiments an attempt was made to 

 determine whether these two effects were independent or not. 



The apparatus was arranged as follows : — 



A loop of pure platinum wire *1 mm. diameter and about 

 8 cms. long was sealed to platinum electrodes passing through 

 glass tubes. These were fitted into a rubber stopper so that 

 the platinum loop could be introduced into the middle of a 

 wide glass tube. 



A brass tube to which a copper wire had been soldered was 

 passed up from the lower end of the glass tube so as to 

 surround the platinum loop, the copper wire being sufficiently 

 rigid to hold it in position out of contact with the glass. This 

 wire also passed through a narrow glass tube fitted into a 

 rubber stopper which closed the end of the glass tube. 



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Hydrogen or air could be passed into the tube through 

 two delivery-tubes passing through the rubber stoppers. The 

 stoppers and various tubes were sealed into position by means 

 of sealing-wax which was found to keep the apparatus 

 sufficiently air-tight. 



The platinum loop was heated by a current from a secondary 

 battery which was measured by an ammeter, and could be 



* See also "On the Discharge of Negative Electricity from Hot 

 O-Icium and from Lime," by F. Horton, Roy. I Soc. Proc. p. 528,. 

 1907. 



