1880.] on Electricity in Transitu. 431 



tlio phenomena of striation. By this, as well as by many other ex- 

 periments, wo have been knl to the coiiclufiion that a stria with its 

 attoiuhmt bhmk space is the i)hysical unit of a striated discharge, and 

 that a striated column is an aggregate of such unities formed by a 

 step-by-step process, the general character of which is indicated in our 

 intermittent discharges. To complete this view of the case, it would 

 not be difficult to show, for we have made many experiments on the 

 subject, that the so-called negative glow is merely a stria localized in 

 position and modified in form by the solid terminal to which it is 

 appended. We have on this account called it an anchored stria. 



One of the most imjiortant consequences following from these 

 experiments is that the discharges at the two terminals are in 

 general independent of one another, excepting as regards the source 

 from whence they come ; and that each is primarily determined by 

 the conditions at its own terminal, and only in a secondary degree, if 

 at all, by the conditions which subsist at the opposite terminal. And 

 since the discharges are not, at all stages of their entire duration 

 (brief though it be), necessarily identical at both terminals, the tube 

 will contain charges of free electricity at different times. A tube, 

 therefore, during the passage of a discharge, is in no respect like a 

 conductor, but is an independent electrical system, having an action 

 very similar to that of an air vessel in a forcing pump. 



This independence of action at each terminal may be illustrated 

 by connecting only one of the conductors of the machine with one of 

 the terminals of the tube, in which case a unipolar discharge will be 

 seen to enter the tube ; and unless it be strong enough of itself to 

 reach the opposite terminal, or at all events within a range of it 

 equal to a blank space, it will return and find exit by the way 

 by which it came. By connecting the two terminals of the tube with 

 one conductor of the machine, a double unipolar discharge will be 

 produced, the two extremities of which will be found to be mutually 

 repulsive. We have not now time to enter into the differences 

 between positive and negative unipolar discharges ; but it will be 

 sufficient at present to remark that they each have, and maintain 

 throughout their existence, the characteristics which belong to them 

 respectively when they form portions of the complete discharge. 



Thus far our attention has been mainly directed to the phenomena 

 displayed by the column of luminosity connected with the positive 

 terminal. The phenomena apj^ertaining to the negative terminal 

 are, however, not less important, as the beautiful experiments of 

 Mr. Crookes have abundantly shown. But in order to study these 

 negative phenomena with advantage we must carry our exhaustion, as 

 he has done, to a much higher degree than in the tubes hitherto used. 

 As the exhaustion proceeds, the positive column gradually shortens, 

 and ultimately shrinks into insignificance, while the discharge from 

 the negative, itself non-luminous, causes a continual projection of 

 gaseous particles from the surface of the terminal, which impinge upon 

 the glass with sufficient violence to cause phosphorescence. These, 



