232 Sir David Salomons, Bart. [June 21, 



scribing this effect, for although to the eye repulsion is evident, it 

 may not, from a scientific point of view, be correct in fact. The 

 appearance may be explained in a variety of ways, but in order to 

 simplify description of the experiments I treat the appearance as a 

 repulsion. However, it must not in consequence be inferred that re- 

 pulsion really does take place. 



The experiments are here given in their logical order, although in 

 point of fact they were not originally made in this sequence. In all 

 investigations it occurs almost invariably that an experiment is made 

 which suggests the previous steps that are necessary to obtain a 

 logical order, and indeed some of these steps are frequently unob- 

 tainable. Therefore, it is very probable that what I believe at pre- 

 sent to be the sequence may yet have missing links. 



Some of the conclusions which may be drawn from the following 

 experiments are : 



That bands may be produced with greater facility in small tubes 

 than in large, and that they become more accentuated probably on 

 account of the inequality of the diameter of such tubes. 



That for the production of bands, the glass of the tube itself ap- 

 pears to play a part, since the bands are difficult to produce unless 

 they reach to the glass of the tube. 



That an exceedingly minute current produces bands which to the 

 eye, in most instances, disappear when the current is somewhat in- 

 creased, and on farther increasing the current they become visible 

 again. I believe that in all previous investigations it has been stated 

 that the bands cannot be produced until a considerable current is 

 passed. I refer to investigations by Messrs. Warren de la Rue, Gassiot, 

 and others. My experiments prove the contrary. The probable reason 

 why these statements were made is due to the fact that with the ap- 

 paratus employed at that time such small currents could not be 

 easily produced. When the minute current is increased, and the 

 bands seem to disappear, I think this is only an optical illusion ; 

 the bands are there, but too faint to be seen, perhaps in conse- 

 quence of the dark bands being so narrow that they escape 

 observation. 



That, when an electric discharge takes place in a large tube in 

 which is placed a partition pierced with a hole, " a forcing effect " 

 frequently appears to be produced. Any bright bands being pro- 

 duced at the hole in the partition may give the appearance of being 

 pushed through to the side of the tube which has the greater length. 

 This phenomenon is mentioned because it is apt to mask many 

 effects, unless the current is suitably adjusted. 



That it is not impossible, after the first trace of light becomes 

 visible in a tube when passing a very minute current, that the dark 

 bands subsequent to this stage are illusory, and that they are really 



