1880.] on Electricity in Transitu. 436 



Proofs of this proposition are to be foimcl in the phenomena of vir- 

 tual shadows, and in other instances of the interference of molecular 

 streams ; but, omitting detailed experiments, the general argument on 

 which the above conclusion is based, is as follows : If two molecular 

 streams, one issuing with positive relief from the side of the tube, the 

 other coming from the negative terminal, show signs of interference, 

 it is clear that the former of these, which certainly started first, must 

 have continued to flow, at all events, until the arrival of the latter. 



The time occtqned by the imssage of electricity of either name along 

 the tube is incomparably shorter than that occupied by the emission of the 

 molecular streams, or (what is the same thing) the time occupied by the 

 negative discharge. 



In support of this conclusion, we have time only for a single 

 experiment ; and, although it is hardly adapted for lecture pur- 

 poses, it is so curious and important that I will venture upon it, in 

 the hope that it may be visible to at least some of the audience. If 

 two pieces of tinfoil connected by a wire be placed, one near the 

 negative, the other near the positive end of a tube through which a 

 negative discharge with a rather long air-spark is passing, the former 

 will show relief (positive) effects, the latter special (negative) effects ; 

 but no i5hosphorescence will be caused at the latter, however long the 

 air-spark used. When the second patch is lifted off the tube and 

 placed upon another through which no current is passing, phospho- 

 rescence is immediately produced. The exjDlanation of this appears 

 to be as follows : The negative electricity, bursting into the tube, 

 summons all the positive which it can draw from the tinfoil. This 

 is answered so promptly, that the second patch gives up to the first 

 througli the medium of the wire all the positive that it can yield, or, 

 which is the same thing, draws off from the first all the negative 

 that it can obtain; and this is done before the advancing negative 

 reaches the distant patch. But so rapidly does the negative advance, 

 that it reaches the distant patch before the molecular streams have 

 had time to flow from the latter in a sufficient stream to produce 

 phosphorescence ; and it reaches it in time to revoTce the supply of 

 positive to the nearer, and to draw back the supj^ly of negative which 

 would have come to, and with it the molecular streams which would 

 otherwise have flowed from the further patch. When the second 

 patch is placed on an independent tube, where no such revocation 

 is possible, phosphorescence actually appears, showing that the revo- 

 cation is no mere supposition, but a real phenomenon. 



From the last two laws, it follows as a consequence that Negative 

 electricity, and therefore also electricity of either name, in the tube out- 

 runs the molecular streams. 



These remarks will give, at all events, some idea of the conclusions 

 to which the present method has led, and of the reasoning upon which 

 those conclusions are based. But the issues of these time-quantities 

 do not begin or end with the mere estimation of their relative magni- 

 tudes ; they suggest questions about the time of formation of a positive 



2 G 2 



