176 Dr. E. Goldstein on the Electric 



caution^ to which I have called attention*, of isochronism in 

 the discharge of such tubes. Observation shows that when 

 the negative rays in one of the tubes excite the luminosity of 

 solid bodies, this is not necessarily the case in the others ; but 

 thov also exhibit the appearance as soon as they are brought 

 to the same degree of exhaustion as the tube which first be- 

 came luminous. 



It follows from this that, in the modification described, the 

 whole of the light about the kathode becomes surrounded with 

 an exterior heterogeneous layer. The position of this new 

 layer is dependent solely upon the position of the wall of the 

 tube, and can be brought into any desired position at any given 

 distance from the kathode by moving the wall to or from the 

 kathode, while the pressure remains constant. It may even 

 be caused to pass, still formed by the ends of the rays, through 

 the outer layer of the kathode-light into one of the inner 

 layers. 



I am not yet in a position to explain the production of this 

 modification of the rays. 



(7) The same differentiation occurs with the u secondary ne- 

 gative light" a name given by me to the light produced at 

 any point of the discharge at which a contraction of the tube 

 is introduced. A mass of light then spreads out from the 

 point where the tube is contracted into the wider portion 

 towards the anode, which possesses, only in a less degree, all 

 the properties known to me of the kathode-light. The point 

 of origin of the negative rays which here make their appear- 

 ance is the last section of the narrow tube which joins the wider 

 portion of the vessel. In the figure (PI. IV. fig. 1) the points 

 a are points of origin of the secondary negative light, whose 

 rays spread out towards /3. The appearance of the modified 

 ray-endings in the case of such rays whose points of origin 

 lie in an open space of gas, shows that the explanation of the 

 appearance is not to be sought in the properties which the 

 kathode possesses as solid body and metallic conductor. 



(8) The excitation of light by the ends of the negative rays is 

 not of the same kind as the illumination called forth in the sur- 

 rounding walls of the tubes by the stratification of the positive 

 light when the rarefaction is small. 



Observation shows that the rays which excite this illumina- 

 tion issue from the whole mass of light ; so that in passing 

 along the column from layer to layer there is observed only 

 uniformly diffused illumination of the wall, even when the 

 stratifications are strongly marked and exhibit great changes 

 in intensity of light. 



* Berl Akad. Ber. August 1871. 



