US ./,(>/ >i<;// Effect of a Magnetic Field, 



The present worls was undertaken with the object of tasting 

 the direct effect of a magnetic field on the ionization current 

 in air at atmospheric pressure when (lie applied voltage is 

 either above or below the saturation voltage. 



§2. Experiment T. Voltage above Saturation. 



Homogeneous secondary X-rays from copper were used. 

 Fig. 1 shows the connections. Primary X-rays from the X-ray 

 tube 1), which was enclosed in the lead box II, fell upon the 

 sheet of copper E which was bent into the shape of a V. This 

 copper was caused to emit secondary X-rays, part of which 

 entered the chamber A through the paper window F and part 

 entered the chamber B through the slit C and the paper win- 

 dow G. The ionization chamber A was placed between the poles 

 of an electromagnet and the other chamber B was outside the 

 magnetic field. The opening of the slit C could be varied by 

 means of a micrometer screw. The ionization chamber A was 

 connected to a positive and the chamber B to a negative volt- 

 age or vice versa, the voltage being such as to give the satura- 

 tion current for both chambers. The inside electrodes of both 

 chambers were connected together and to a Wilson tilted 

 electroscope as shown. The chamber A was made of lead, the 

 inside being coated with paper in order to cut out the effect of 

 secondary cathode rays from the lead. The dimensions of A 

 were 7*5 X 2 - 30 X l'O cm 3 , the X-rays entered through a win- 

 dow 1'Ox 1'5 cm 3 and travelled for a distance of about 2 - 3 cms. 

 in the chamber. The inside electrode was a wire which could 

 be extended to various lengths along the middle line of the 

 chamber A in order to vary the saturation voltage. With this 

 arrangement the reading of the slit opening when there was no 

 deflection of the electroscope was taken as a measure of the 

 ionization current in the chamber A. Any variation in the 

 primary X-rays produced proportional changes in the total 

 ionization in the two chambers and thus any fluctuation in the 

 strength of the primary X-rays was compensated. The electro- 

 magnet being necessarily near the X-ray tube, the bright spot 

 on the anti-cathode was deflected by the magnetic field. This 

 was partially overcome by means of a compensating magnet. 

 The strength of the magnetic field was found by means of an 

 exploring coil and a ballistic galvanometer in the usual way. 



In this experiment the effect of a magnetic field on the total 

 ionization produced by X-rays was examined. The results are 

 shown in Table I. 



This table shows that the magnetic field, and consequently 

 the bending of the secondary cathode rays into curvilinear 

 paths, does not alter the total ionization produced in a gas by 

 X-rays. 



