370 . Prof. C. Slieard. on the 



prove that the bombardment theory does not represent even 

 to a small extent what takes place when secondary fluorescent 

 radiation is produced. That is, fluorescent radiation cannot, 

 be an indirect effect o£ /3-ray activity. 



In addition, it will be noticed that in the case of radiator I. 

 there is much less ionization in the gold than is the case in 

 radiator II. So that this experiment seems to negative those 

 theories which assume that it is on recombination o£ the gold 

 atoms that the fluorescent X-radiation is produced. 



The evidence of this paper strengthens the theory put 

 forward by Professor Barkla *, and supported by later paper?, 

 namely, that the atom from which the electron is ejected is 

 the seat of production of the radiation. 



Summary. 



The paper deals with Professor Bragg's theory that the 

 fluorescent X-radiation is produced indirectly by the action 

 of the expelled /3-rays, and not by the direct action of the 

 primary beam. 



His criticisms of a previous paper in w r hich an experiment 

 is described to test this theory have been discussed. 



Another experiment has been performed, in which the 

 theoretical objections he raised have been obviated. The 

 results obtained agree precisely with those given previously, 

 and indicate that Professor Bragg's bombardment theory 

 does not represent even to a small extent the process of 

 production of the fluorescent Rontgen radiation. 



In conclusion, I wish to express my thanks to Professor 



Barkla for his continued help and advice. 



Wheatstone Laboratory, 

 King's College. 



XXXIX. The Ionization produced by Heated Salts. By 

 Charles Sheard, M.A., Assistant Professor of Physics, 

 Ohio State University, and Fellow in Physics, Princeton 

 University^ . 



INVESTIGATIONS have been made in recent years upon 

 the existence of positive and negative emissions from 

 heated salts and upon the values of e/m of the emitted ions. 

 Many substances have been examined as to their ionizing 



* Jalirbiich der JRadioahtivitiit und Elektronik, iii. (1908). 



f Communicated by Professor O. W. Richardson. Read before the 

 American Physical Societv, New York Meeting, March 2nd, 1912. See 

 Abstract, Phys. Rev. xxxv. pp. 234- 236, 1912. " 



