Recent Results of Northlight Investigations. 1019 



down in the filament varied between 6 and 8 volts during 

 these experiments. The curves show radiation setting in 

 at 356 volts. It is difficult to see how this point can lie 

 outside the limits 354-358 volts in view of these experi- 

 ments. As in the case of carbon, the two corrections practi- 

 cally cancel each other. The corresponding wave-length 

 limits are 34'6 to 35'0 A.U. and the probable value 34'8 A.U. 

 Calculating from an empirical formula given by Vegard * 

 for the M a line, 



z,/R= r J T N 2 -2-37Nf40, 



where v is the frequency, R Rydberg's constant, and N the 

 atomic number, the extrnpolated wave-length for the Ma 

 line for molybdenum is found to be 35'2 A.U. As we 

 should expect the radiations to be excited by a voltage 

 corresponding to a frequency somewhat higher than that of 

 the ol line of the series, we see that there is good ground for 

 identifying the phenomena here investigated with the exci- 

 tation of the M X-rays of molybdenum. 



The ultimate objective of the experiments is to examine 

 the frequencies of the emitted radiations by measuring the 

 energy of the electrons which they liberate by photoelectric 

 action. We believe that this apparatus is capable of giving 

 the desired information, and the work is being carried for- 

 ward at the present time. During the past three years similar 

 measurements have been made by one of us (C. B. B.) on 

 sodium, potassium, and lithium, on which it is hoped shortly 

 to publish results. During 1919-20 some tests were made in 

 the Wheatstone Laboratory by Mr. Gr. Williamson, using 

 lithium salts and carbon, and by Dr. Holtsmark with carbon. 

 Whilst these experiments did not lead to results which 

 seemed unequivocal, we feel that we have probably profited 

 through the experience gained thereby. 



CVII. Remark concerning Professor Vegard' s Paper entitled 

 " Recent Results of Northlight Investigations and the 

 Nature of the Cosmic Electric Rays." By Professor Carl 

 Stormer, Christiania j. 



IN consequence of a paper appearing under the above title 

 in the Philosophical Magazine for July, 1921,1 beg 

 to draw attention to the work I have recently completed, 

 and which appeared at the beginning of July last in Geo- 

 fysiske Publikationer, vol. 1. No. 5, Christiania, under the 

 title " Rapport sur une expedition d'aurores boreales a 

 Bossekop et Store Korsnes pendant le printemps de Tannee 

 1913/' 269 pages with 104 plates. 



* Phil. Mag', vol. xxxv. p. 316 (1918). 

 f Communicated by the Author. 



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