430 



Mr Waran, On the effect of a 7nagnetic field 



decrease in cross-section of the discharge brought about by the 

 deflecting action of the field. From Fig. 1 it was seen that the 

 discharge is pushed on either side into two thin filaments leaving 

 the centre of the tube more or less free, thus reducing the effective 

 cross-section of the discharge. They regard it as tantamount to 

 a change to a narrower capillary. But that the effect is not entirely 

 due to this can be shown by the following considerations. 



Though a narrower capillary does generally tend to enhance 

 the weaker lines and bring about a trace of continuous spectrum, 

 its effect is not of such a selective nature tending to the enhance- 

 ment of some lines previously almost invisible, at the same time 

 decreasing the intensity of some others as observed in the case of 

 mercury and many other gaseous spectra. 

 Further the effect of the field is to weaken the 

 continuous spectra in many cases though under 

 the same circumstances a narrower capillary 

 tends to intensify the continuous spectrum. 



To test this point further a tube of the 

 form shown in Fig. 3, in which the capillary 

 portion was made of two sections in series^ 

 with sectional areas in the ratio of about 10:1, 

 was made and placed transverse to the field as 

 indicated. An image of the portion of the tube 

 between A and B was thrown on the slit of the 

 spectroscope and the spectra given by these 

 two capillaries were compared. There was very 

 little change except that the portion of the 

 spectrum corresponding to the narrower capil- 

 lary was distinctly brighter throughout the 

 whole spectrum. A magnetic field was now 

 applied transversely at A to see how far the 

 narrowed section of the discharge through A 

 gave a spectrum resembling that given by B^ 

 The change introduced by the field was quite 

 different. With hydrogen at low pressure, while 

 the effect of the narrowed capillary B was ta 

 increase the intensity of the hydrogen lines the effect of the field 

 on A was to decrease the intensity of the hydrogen to a slight 

 extent and increase the intensity of the mercury lines as shown 

 in Fig. 4 (1). Such results clearly show that though the decrease 

 in the cross-section may be the cause of some of the changes ob- 

 served, yet there are others that cannot go under this simple 

 explanation and they point to the existence of some other influence 

 exerted by the magnetic field. 



Further, experimenting with a tube of the form illustrated 

 below, Fig. 5, in which the discharge is in the direction of the 



Fig. 3. 



