560 Prof. L. Vegard on the Spectrum 



I used a cylindrical tube of the form shown in the figure 

 and of the very same type as those used in the experiments 

 of Wilsar on the Doppler effect of hydrogen lines. The 

 rays pass through a narrow boring in the cylindrical cathode 

 to the observation chamber, which ends in a glass tube about 

 5 cm. long and 0*75 cm. diameter. 



This narrow glass tube was placed between the poles of a 

 strong electromagnet, in the way shown in the figure, and 

 the rays could be made to pass a strong magnetic field of 

 11,500 gauss for a distance of 4*2 cm. The luminosity was 

 analysed and measured at the end of the glass tube by 

 means of a spectrograph of high light-power and a suitable 

 dispersion for observations of the Doppler effect. The 

 direction of the collimator axis formed an angle of about 35° 

 with the direction of the rays, and it was thus obtained that 

 only light from the very end of the glass tube passed into 

 the spectrograph. 



During discharge a constant current of hydrogen was 

 maintained by continual pumping. By a simple arrange- 

 ment, the direction of the current of the gas through the 

 boring in the cathode could be reversed ; and in this way 

 the potential of the discharge-tube could be changed inde- 

 pendently of the pressure in the observation chamber. The 

 discharge-tube was surrounded by a thick cylinder of soft 

 iron, to prevent the magnetism from exercising an influence 

 on the discharge. The spectrograms were taken under 

 the very same discharge conditions, with and without a 

 magnetic field, and for some different pressures. When the 

 magnetic field was put on, the positively-charged rays were 

 driven into the wall as soon as they v. ere formed, and the 

 luminosity at the end was mainly produced by uncharged 

 particles, and most of the moved intensity was emitted from 

 rays in the neutral state. 



By means of the idea of the mean free path of the positive 

 rays introduced by W. Wien *, we can calculate the dimin- 

 ution of light-intensity which would be produced by the 

 magnetic field provided that the light was entirely emitted 

 from the. neutral rays. 



Let us consider a cross-section (A-B) of the bundle just 

 before the rays enter into the magnetic field ; and let us 

 suppose that the bundle at this place has reached statistical 

 equilibrium, so that the ratio between the number of charged 

 and uncharged particles would remain constant provided 

 there was no magnetic field. 



* W. Wien, Ann. d. Phys. vol. xxxix. p. 519 (1912). 



