252 Sir David Salomons on the Electric 



refuses to travel that road, though possibly some indirect 

 method might be devised. 



Another conclusion may also be deduced from this experi- 

 ment. It is that since the bands become more numerous in the 

 strongest part of the field, they are produced by self-inductive 

 effects. To put this in unscientific language, the discharge is 

 comparable to that of a lightning-discharge through a good 

 conductor, the peculiarities of which were first pointed out by 

 Professor Hughes ; that is to say, the discharge of the current 

 through the gas is checked, and then proceeds again, checked 

 again, and so on ; and it is fairly evident that at the points of 

 these various checks heat is developed, and the residual matter 

 in the tube raised to a high temperature, producing what are 

 termed bright bands. That the bright bands consist of heated 

 matter is most probable for the reason that they may be seen 

 from all points of view. 



If instead of employing the alternate current the induction- 

 coil is so adjusted as to produce an intermittent direct one, 

 only one line of bands appears, equatorially placed, on one 

 side or the other, according as the current is in one direction 

 or the opposite one. The analysis of the column of bands is 

 the same as that of one of the columns when the alternate 

 current is employed. Reversing the current through the tube 

 has no effect upon the appearance of the tube, since the 

 currents change sides. But if the poles of the magnet are 

 reversed, then the convexity of the column of bands becomes 

 reversed ; and this, of course, would be expected. 



It has already been stated that when the current flowing 

 through the tube is exceedingly small, the tube remains dark 

 and no current would appear to pass. It seems to me that 

 the probable explanation for this is that the current is, so to 

 speak, driven into the glass, which has so high a resistance 

 that no appreciable amount passes. In fact, the whole of the 

 experiments show that the larger the amount of the current 

 which flows through the tube, the more nearly do the bands 

 approach to the centre, or, in other words, the smaller is the 

 space at the centre of the tube which appears dark. 



If the tube, with the current flowing through it, is placed 

 in an unsymmetrical field, then the lines of bands become 

 distorted, more or less spiral in form. This is because the 



Fig. 10. 



°^ } n ) ) ) )))))))) ^r 



field being unsymmetrical the currents tend to take up dif- 

 ferent positions in various portions of the tube (see fig. 10). 



