TROWBRIDGE. — ELECTRIC DISCHARGES. 639 



Figure 8 is a photograph of the X-ray bulb when the cathode mirror 

 has been made the magnetic pole. Without the excitement of the mag- 

 netic field the bulb could not be made to give the X-rays even with a 

 coil producing a six-inch spark, the vacuum having increased greatly 

 during the previous use of the bulb. When the field was excited, how- 

 ever, a brilliant fluorescence was produced without any appearance of 

 X-rays. The negative ions apparently did not reach the anticathode, 

 but instead formed fluorescent rings around the cathode. The cathode 

 is thus made part of a hollow hemisphere of, in this case, orange light. 

 When, however, the bulb was excited by a coil giving a twenty-inch 

 spark with Leyden jars, the bulb gave very brilliant X-rays at the 

 moment of exciting the magnetic field. In the case of the use of the 

 six inch spark coil there were no Leyden jars in the circuit. 



Besides the scientific side of the manifestations of the effect of the 

 magnetic field on discharges in high vacua, there seems to be a practical 

 use of the electro-magnetic field in connection with the regulation of the 

 discharge in X-ray bulbs. At present, when the vacuum has risen so 

 high that the bulb cannot be excited, one is forced to apply heat to 

 various regulators in order to drive out gases to increase the conduction. 

 All regulators hitherto used are uncertain and dangerous to the life of 

 the bulb in their application. I believe that a magnetic regulator 

 applied to the anode would be of great service in hospital plants where 

 a suitable electrical equipment can be had. The magnetic regulator is 

 entirely safe and is constant in its action. It also enables one to pass 

 readily from the production of hard rays to that of soft rays by the 

 modification of the strength of the magnetic field, a modification difficult 

 to accomplish without the application of the magnetic field. 



In Experiment 1 can we not say that the revolving factor in the case 

 of the negative ion is greater than its progression factor ? The energy, 

 therefore, along the line of discharge is less to oppose the energy of the 

 positive ion, and the negative ion is therefore diverted from the line of 

 discharge, thus allowing the positive column to advance to the cathode. 



In Experiment 5 the revolving factor is less than the progression fac- 

 tor, the discharge is ejected from the centre of the magnetic field. This 

 is independent of the name of the magnetic pole. 



In Experiment 6 the revolution of the cathode light indicates this 

 superior revolution factor in the case of the negative particle. This is 

 independent of the name of the magnetic pole. 



In Experiment 10 we see the positive particles driving back the nega- 

 tive particles so as to diminish the dark cathode space. 



