Current of Electricity from a hot Platinum Wire, etc. 501 



to be pushed forward so as to surround the electrodes when the 

 wire was in its position between the electrodes. The introduction 

 of this earth-connected cylinder was the most important feature 

 in this new apparatus. For it is now found that, in general, even 

 at very high temperatures by far the greater part of the discharge 

 could be stopped by the magnetic field. If, however, the platinum 

 cylinder was disconnected from the earth then at the higher 

 temperatures the discharge was practically unaffected by the 

 magnetic field. 



As is well known, the negative discharge from platinum exhibits 

 great irregularities. Dr A. H. Wilson has shown (Phil. Trans. 

 A, Vol. 202, pp. 243-275, 1903) that these irregularities can be 

 very largely got rid of by boiling the wire in nitric acid and by 

 driving occluded gases out of the wire by continuous heating. 

 The object of this investigation, however, being to obtain informa- 

 tion with regard to the mechanism of the discharge from 

 platinum in general, experiments were made with wires exhibiting 

 different degrees of irregularity depending upon their previous 

 treatment. 



The results given below represent the main conclusions 

 arrived at. 



Table II. gives the variation of the discharge with the 

 potential. After setting the wire up in the plane of the plati- 

 num disc, the latter was dipped into cold nitric acid and then 

 rinsed in distilled water. Temperature of wire = 795° C. 



Table II. 

 Oct. 17, 1903. Wire I. Pressure 0-011 mm. 



The numbers given in the above table have been plotted in 

 Diagram II. 



