Discharge in a Magnetic Field. 247 



took place. I soon found that a vast number of the pheno- 

 mena described as fundamental were superposed phenomena ; 

 and that when exceedingly small E.M.F. was employed the 

 various phenomena were seen in their purity, and on raising 

 the E.M.F. the various changes could be seen, up to the 

 complex appearance described in some of the early papers. 

 The E.M.F. employed in the following experiments was 

 sometimes as low as 700 volts and rarely over 2000. 



It has been known for a long time that the discharge 

 through the vacuum-tube is affected by the magnetic field, 

 but beyond this circumstance I cannot find anything that has 

 been published upon the subject classifying results. 



Having worked to that point when I could conirol what 

 took place within the tube, it became a comparatively easy 

 matter to investigate the discharge in the magnetic field 

 provided a sufficiently powerful magnet could be obtained. 



All the electromagnets in existence were built on the 

 Faraday-magnet type, and this pattern was found incon- 

 venient. I therefore had a special magnet constructed 

 weighing 13 cwt., with a field probably far more powerful 

 than any which had been made before, with the polepieces 

 capable of being approached and distanced by means of 

 screws, and a variety of other details introduced which made 

 the apparatus a piece of engineering work as well as one 

 suitable for scientific investigation. This magnet is shown 

 in fig. 1. 



I will not repeat what I have already published on the 

 subject beyond referring to tw r o points : — 



Firstly, that the glass of the tube has a considerable influ- 

 ence in creating the bands ; and 



Secondly, that the bands as generally seen are spurious, 

 and can only be viewed in their purity at the moment when 

 the current is so reduced that they disappear from view. 



There may be other stages beyond this point which the eye 

 cannot see, and that such is probable is shown from the fact 

 that when the tube is made of fluorescent glass the current may 

 be still further reduced and the bands be visible. 



For producing the current I employed Apps's coils of 

 various sizes, the contact-breakers being special mechanical 

 forms devised by myself, and worked by an electro-motor. 

 I also employed the alternate current from an alternator, 

 raised to a suitable pressure by means of a transformer. 



The induction-coils had primary coils so wound that a 100- 

 volt current could be put on direct, without the insertion of 

 a resistance. The number of turns of wire in the primaries 

 is so great that the self-induction reduces the length of the 



