36 ' Prof. E. Wiedemann on the 



There are also a series of interesting facts which have been 

 clearly observed, but of many of which it was not possible for 

 the same reason to determine the intimate connexion, by 

 which remark it is of course not intended in any way to 

 depreciate the work of the earlier investigators. 



The separate details have only gradually become of import- 

 ance, and even now it is often difficult to recognize them 

 accurately in descriptions. I have endeavoured in the subjects 

 of which I treat to distinguish these relationships as accurately 

 as possible, and to make clear the conditions under which the 

 phenomena occur. 



In order to fix ideas we will agree upon the following 

 nomenclature : — The phenomena are best observed in tubes 

 having electrodes of a flat shape, because then the different 

 stratifications are formed at right angles to the axis of the tube. 



If k (fig. 3) is the kathode, scarcely any light is to be seen 

 in the part of the tube next it — this we will call the dark 

 negative space ; next to this comes a stratification (6), sharply 

 bounded on the side next the kathode, the bright negative layer. 

 From it issues light (b p) towards the anode, which becomes 

 continually fainter ; this we will call the gloiv-rays. They 

 are separated from the positive column of stratified light, of 

 which the first layer is p, by a dark space hp which may be 

 called the dividing space. The whole is traversed by the 

 kathode-rays Im issuing from the kathode k. 



1. Influence of Interposed Resistances. — The experiments 

 were so arranged that the one pole of the electrophoric machine 

 was connected with the earth, whilst the other was in connex- 

 ion with one electrode of the tube, the other electrode being 

 connected through the coils of a galvanometer with the earth. 

 Resistances could be introduced either between the discharge- 

 tube and the machine, or between the discharge-tube and the 

 earth. They consisted of long glass tubes on the outside 

 coated with shellac, and filled with distilled water in which 

 conducting wires plunged. The discharge was observed in a 

 mirror rotating with moderate velocity. 



The result generally obtained was that, whether resistances 

 were included or not, the deflection of the galvanometer was 

 the same during uniform action of the machine, and that 

 consequently the quantity of electricity passing through the 

 discharge-tube in unit time was always the same. 



The number of discharges, however, was found to be con- 

 siderably greater when resistances were employed than with- 

 out, and the same result was obtained at very different pressures. 

 With discharge-tubes of the form usual to spectral-tubes the 

 discharge is always discontinuous. With wider discharge-tubes 



