from heated phosphorus compounds. 333 



but was deflected in the positive direction in strong fields. These 

 rays were evidently anode rays similar to those obtained by 

 Gehrcke and Reichenheim. The spectrum showed some calcium 

 lines and other lines which could not be identified in the short 

 time during which the rays persisted. Thus we see that anode 

 rays can be obtained from calcium phosphide, although they could 

 not be produced from the phosphates experimented with. 



Gehrcke and Reichenheim have connected the production of 

 anode rays from the halogen salts of the alkalis and alkaline 

 earths with their easy fusibility and their property of dissociating 

 when strongly heated. The heated salt is supposed to be decom- 

 posed electrolytically by the passage of the current, the metal 

 being liberated at the surface of the anode and travelling across 

 the tube. Close to the anode the electric force is very strong on 

 account of the anode fall of potential, and it is in traversing this 

 region that the liberated metal atoms obtain their great velocity. 

 Some time ago it was shown by Matthies* that the anode fall in 

 a vacuum tube was greatly increased by the presence of a halogen 

 vapour. In a recent paper Reichenheim -f states that, at low pressures 

 and with large currents, the anode fall in the halogens amounts 

 to several thousand volts. This abnormally high value Reichen- 

 heim thinks maybe explained on the supposition that the halogen 

 vapours possess, in a higher degree than other gases, the power of 

 absorbing negative electrons. If this be correct, other electro-nega- 

 tive vapours should behave in a similar manner, and Reichenheim 

 shows that a large anode fall is also obtained in phosphorus 

 vapour. In the experiments described in this paper it is probable 

 that phosphorus vapour was present in the case of the calcium 

 phosphide anode, owing to its decomposition when heated. There 

 would thus be a large anode fall and a strong force near the anode 

 which would give to the liberated atoms the energy to make them 

 luminous anode rays. The phosphates, on the other hand, are 

 extremely stable bodies, and in their case there would be no 

 phosphorus vapour to cause an abnormal anode fall and con- 

 sequently no anode rays. Thus these experiments seem to confirm 

 the view of Gehrcke and Reichenheim as to the origin of anode 

 rays, and to show that there is no connection between this pheno- 

 menon and the emission of positive electrification from heated 

 salts. 



The author wishes to acknowledge his indebtedness to the 

 Government Grant Committee of the Royal Society for the means 

 of purchasing some of the apparatus used in these experiments. 



* Matthies, Ann. der Phys. xviii. p. 473, 1905. 



t Reichenheim, Verh. d. D. Phys. Ges. p. 168, 1909. 



