156 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
and has since engaged the attention of so many physicists. Our excellent and highly 
esteemed friend the late Mr. Gassiot, working at first with an induction coil, but more 
recently on the same lines as ourselves (voltaic batteries of high potential*), has pub- 
lished results of great interest, many of which are confirmed by our own experience ; 
while, on the other hand, we have enjoyed pleasurable intercourse and exchange ot 
thought with our contemporary, Mr. W. Spottiswoode, who is still pursuing with 
great acumen and originality a similar investigation, both with the induction coil 
and the Holtz machine, with which he has recently used condensers of great capacity, 
like those we employ and have described in Part I. If we arrive at the same results 
by different paths, the one investigation will support the other, and for each may be 
claimed more reliance than if unconfirmed. 
Throughout our labours we have felt so strongly the necessity of obtaining numerical 
results as data for the foundation of a theory, that we have not hesitated to risk much 
in this cause. By the fusion of terminals, or the sudden discharge of the condenser, 
we have lost a vast number of very beautiful tubes ; but gradually, by the adoption 
of various devices, and by the employment of instruments specially constructed and 
insulated to suit the high potentials we deal with, we have succeeded in overcoming 
the various impediments, so that we can now readily obtain values for the physical 
quantities that enter into consideration in our experiments. 
There is a serious trouble connected with the study of the discharge in rarefied 
gases, for, after a very short time, the tubes completely and permanently change, so 
as no longer to present the splendid stratifications witnessed on a first trial. We 
believe these changes occur much more rapidly with the battery, in consequence of 
the greater amount of current, than with the induction coil ; but the fact appears to 
be well known to Hr. Geissler, of Bonn, who, on the occasion of a visit to our 
laboratory, brought with him some tubes through which no current had previously 
passed (virgin tubes, as he calls them), which presented most beautiful phenomena 
lost for ever after too brief a period. 
Tube 123 (Cyanogen), for example, when first connected with the battery, presented 
strata which completely filled the tube without leaving a dark space near the negative, 
negative (a point), where there was a dark interval: he says, “ De plus, cette flamme ou aigrette qui part 
du pole positif presente notamment a sa partie superieure (en supposant la pointe negative en haut) 
des zones alternativement obscures et lumineuses. Ces zones sont concaves vers la boule quand la pointe 
(negative) est rapprochee de cette derniere ; elles deviennent convexes vers la boule lorsque la pointe en 
est tres-ecartee.” 
* Mr. Gassiot made several batteries of different kinds in the course of his experiments; on the occasion 
of a visit to his laboratory, January 26, 1875, the current of his Leclanche battery was measured by us 
with a voltameter. The current of 1000 new cells was found to be 0 - 07464 W ; that of the whole 
3000 cells, 1000 of which had been a long time in use, 0'04718 W. Taking the Leclanche as l - 48 volt 
the internal resistance of the new battery must have been 19'83 ohms per cell ; that of the whole 3000, 
31'37 ohms per cell. The striking distance of the whole 3000 between a conical point and a disc 0T25 inch 
diameter was only 0'025 inch ; whence the inference is that the insulation was, at that time, imperfect. 
