306 Mr. G. H. Martyn on the Discharge 



determine the number of ions (n) at the surface of the metal 

 which are affected by the various forces, these forces being 

 proportional to the square root of the intensity. 



The experiments show that for small intensities, n diminishes 

 much more rapidly than F 2 , so that it may be that for very 

 small forces n would be zero. 



In conclusion I wish to acknowledge my indebtedness to 

 Professor Town send, in whose laboratory the experiments 

 were performed, for his kindly interest and valuable sug- 

 gestions throughout the course of the investigation. 



XXY. The Discharge of Electricity from Hot Bodies. By 

 G. H. Maetyn, B.Sc, Wheatstone Laboratory, King's 

 College, London *. 



[Plate X.] 



THE following paper contains an account of some expe- 

 riments on the rate of loss of electricity from negatively 

 charged hot platinum in air and in hydrogen at atmospheric 

 pressure, and also on the effect on the rate of loss produced 

 by coating the wire with calcium oxide. 



H. A.Wilson (Phil. Trans. A. vol. cxcvii. 1901) measured 

 the leak from hot platinum in air at various temperatures, 

 and showed that the energy required to produce an ion could 

 be calculated from the rate of variation of the leak (#), due 

 to a small difference of potential, with the absolute tempe- 

 rature (0) by means of the formula 



/l 1\ , xfO* 



where Q is the energy required to produce one gram-mole- 

 cular weight of ions of either sign. 



0. W. Richardson showed (Phil. Trans. A. p. 343, 1903) 

 that the negative leak from hot platinum in gas at low 

 pressures could be represented by a formula of the type 



where <£ = the current per square centimetre, — the absolute 

 temperature, and A is a constant. 



H. A. Wilson found' (Phil. Trans. A. p. 352, 1903) that 

 the leak in hydrogen was enormously greater than in a 

 vacuum. 



* Communicated by Prof. H. A. Wilson, F.R.S. 



