166 Dr. T. Preston on Radiation Phenomena 



not be ignored till it had been proved by experiment that the 

 modifications were actually caused by other agencies, and 

 this I endeavoured to do by two lines of attack. 



In the first place, if these phenomena are due to reversal, it 

 is likely that they will cease to exist when the quantity of 

 vapour in the source of light is greatly reduced. I accord- 

 ingly tried sparking with weak solutions of salts instead of 

 with metallic electrodes, but in no case did the quartets, or 

 other modifications, reduce to the triplet form, but on the 

 contrary they became clearer and more precise as the lines 

 became sharper with the reduced quantity of vapour. Never- 

 theless this was not regarded as conclusive or even seriously 

 in opposition to the supposition of reversal, for the appearance 

 of reversed lines in the strong magnetic field when the spark 

 is blown about might differ from that of an ordinary reversal. 



I accordingly endeavoured to gradually increase the strength 

 of the magnetic field and observe if the components of the 

 supposed reversed line remained at the same distance apart 

 or became more widely separated as the strength of the field 

 increased. The extent to which I w 7 as able to increase the 

 field at that time was not, however, sufficient to enable me to 

 determine with sufficient certainty whether the reversal 

 hypothesis was tenable or not. For although the com- 

 ponents of the supposed reversed line appeared to separate 

 under the increased field, yet this separation was not suffi- 

 ciently great to overthrow the reversal hypothesis, for it 

 might be said that the absorbed band along the middle of the 

 line had merely become a little wider. The weight of 

 evidence, however, appeared to be against the reversal theory; 

 and in order to further test this matter I had a powerful 

 electromagnet specially built which it was hoped would 

 furnish a field sufficiently strong to determine matters 

 decisively, and in this respect it has not disappointed expect- 

 ation. Thanks to the courtesy of the University Authorities 

 and of the Curator, Dr. W. E. Adeney *, I was able to resume 

 work at the Royal University with improved apparatus, and 

 it was soon found that the reversal theory must be abandoned 

 and that the explanation of the various deviations from the 

 normal triplet-types must be sought for in other agencies. 



Before describing these more recent results, it will render 

 the explanation more intelligible if we refer for a moment to 

 figs. 1, 2, 3, 4, In fig. 1 the three lines A, B, C are 



* I am deeply indebted to Dr. Adeney throughout this and the 

 previous investigations, for he invited me to the Royal University 

 laboratories and facilitated my work under conditions which necessarily 

 interfered with his own researches. 



