TROWBRIDGE. — ELECTRIC DISCHARGES. 637 



the direction being dependent naturally upon the direction of the cur- 

 rent and the polarity of the field. The space around the anode was 

 cleared of the striae, which existed before the field was excited ; but the 

 striations just beyond the most intense portion of the field were broken 

 up into smaller striae. 



8. The electro-magnet was placed at right angles to the cathode. 

 The discharge was thrown up or down according to known electro-mag- 

 netic laws, but in addition striae were formed at a stage of pressure far 

 below the ordinary stratification stage, at pressures of 2 cm. to .5 mm. 



9. The electro-magnet was placed at right angles to the discharge at 

 a distance from either electrode, in the centre of the tube (Figure 5). 

 What may be called the magnetic striae appeared on the diverted path 

 of discharge. These striae only appear with strong currents at compara- 

 tively high pressures, 2 cm. to .5 mm. 



10. The ordinary form of X-ray bulb does not lend itself easily to the 

 application of the magnetic field, either at the anode or the cathode ; and 

 even in the special form of bulb which I have used in this investigation 

 it was not possible to develop magnetic lines of force over the entire sur- 

 face of the anode or the cathode. The cores of the electro-magnets were 

 hollow in order to allow of the approach of the coil of the electro-mag- 

 net to the terminals of^ the bulb, the glass seals of these terminals thus 

 projecting into the hollow iron cores ; only a circular area, therefore, on 

 the cathode or anode forms the effective magnetic field. It seems prob- 

 able that the best results would be obtained by inclosing the iron cores 

 entirely inside the bulb, platinizing the end of the iron core forming the 

 anode, placing the aluminum mirror forming the cathode directly in the 

 end of an iron core and nickel plating both iron cores to prevent 

 the constant escape of gases from such large surfaces of iron. I had a 

 bulb constructed of this general description, but found it impossible to 

 exhaust it to the X-ray stage on account of the escape of gases from the 

 iron ; the iron was not nickel-plated, however. The bulb was exhausted 

 while it was strongly heated in an oven. 



Figure 6 is a photograph of the discharge in the X-ray bulb somewhat 

 before the X-ray stage ; a dark space surrounds the cathode. 



Figure 7 is a photograph of the same tube when the magnetic field is 

 applied to the anode. This cone of rays is solid until just before the 

 X-ray stage ; then it becomes hollow ; and at the X-ray stage it appears 

 only at the instant the magnetic field is excited as a violet light, and 

 then becomes indistinguishable in the fluorescence of the bulb. A violet 

 brush, however, persists on the surface of the anode at the X-ray stage. 



