Heating Effects at the Anode in Vacuum-Tubes. 189 



based on a calculation of the actual value of the diffusion 

 coefficient of hydrogen atoms through ordinary hydrogen. 

 The present results show that the actual degree o£ dissocia- 

 tion is much smaller than that previously found, and that 

 even at 3500° K. hydrogen is probably not dissociated to a 

 very great extent. It is hoped that the experiments at very 

 low pressures will make possible a quantitative estimation of 

 the degree of dissociation. 



In conclusion, the writer wishes to point out that the value 

 of 130,000 calories referred to by Bohr is undoubtedly too 

 high, and that the experimental evidence now indicates a 

 value of about 75,000 to 80,000 calories. That the correct 

 value, however, is as low as the 60,000 calculated by Bohr 

 seems very improbable. 



XIX. Heating Effects at the Anode in Vacuum- Tubes. By 

 B. Hodgson, M.Sc, Ph.D., Assistant Lecturer in Physics, 

 Ihe University, Bristol *. 



§1. TX a previous communication f the author showed 

 JL that the energy communicated to the anode during 

 discharge in air was approximately proportional to the 

 current through the tube. The experiments were made with 

 gas-pressures 2*7, 1*05, and 0*63 mm. The experiments to 

 be described have been carried out over a large range of 

 currents and pressures in oxygen. The apparatus used was 

 that described in earlier papers %. The method of experi- 

 menting was slightly altered. Instead of allowing the anode 

 to rise to that temperature at which the loss of energy by 

 radiation was equal to the gain from the bombardment of 

 negative carriers, the rise in temperature in a definite 

 interval of time was measured and a correction for loss by 

 radiation applied. This method was found to yield results 

 much more quickly with only a small loss in accuracy. The 

 anode used was of lead, and had a heat capacity of 2*2 gm. 

 calories. 



§ 2. Experimental Results. 



The results in Table I. show the heat energy received 

 by the anode in one second for currents varying from 

 O'OOl amp. to 0*007 amp. and pressures between 3'8 mm. and 



* Communicated by the Author. 

 t Hodgson, Phil. Mag. xxv. p. 458 (1913). 



X Hodgson, Phil. Mag. xxv. p. 453 (1913) : Hodgson & Maiustone, 

 Phil. Mag. xxvi. p. 411 (1913). 



