1894.] 



On some Phenomena in Vacuum-tubes. 



233 



the bright bands ; and what appear to be the bright bands consist of 

 overlaps which produce double the brightness of the so-called dark 

 bands. In reality, therefore, the bright bands indicate the position 

 of the dark bands. (See fig. A.) 



Case 1. 



A = Bright bands. B = Dark bands. 

 Case 2. 



Bright bands A expanded overlap at dark spaces B, which now appear twice as 



bright as at A, and the spaces A appear dark by contrast. 



Fia. A. 



That by devices bands can be produced in a large tube occupying 

 only a small portion of the cross sectional area, at any rate so far as 

 the eye can discern. 



That, when employing Professor Crookes' tubes for illustrating 

 experiments on radiant matter, if suitable conditions are observed, 

 strise are formed in these tubes. 



That, in tubes having exceedingly small electrodes, and apparently 

 not capable of producing striae, these can be shown to exist if very 

 minute currents are employed. 



That the tube, when made to act as a condenser, permits more 

 current to pass. 



That from the above considerations it is not unlikely that a view, 

 which has been held, in regard to the probable origin of the bands, 

 that they consist of a series of discharges through the tube, is true ; 

 that the nature of such discharge can be varied by suitable devices 

 placed within the tubes, and that the examination of the nature of 

 the discharge can be best made with very minute currents, that is to 

 say, currents so small that, if made any less, the tube would no longer 

 show any sign of light. 



(N.B. The number against each figure corresponds with the 

 number of the experiment. This accounts for the absence of fig. 10. 

 The experiments were made with the tubes supported horizontally 

 (with the exception of tube fig. 12). This position was chosen for 

 the sake of convenience, the results being the same for all positions. 

 Tube fig. 14 must be placed horizontally in order to shift the movable 

 disk). ~ 



