4 
DES. J. PLUCKEE AND J. W. HITTOEF ON THE 
greasing the stopcocks. (The oxygen simultaneously obtained by decomposition is not 
indicated.) The hydrogen-lines given by spectral tubes made of common glass are 
more brilliant than those of tubes made of less fusible glass, the hygroscopic state of the 
glass not being the same in both cases. Though within the interior of the exhauster 
the air is in contact with the surface of concentrated English sulphuric acid, or, what is 
preferable, with anhydrous phosphoric acid, we never succeeded in expelling the last traces 
of hygroscopic water, not even by strongly heating the spectral tube during evacuation. 
If, in the usual way, a Leyden jar be intercalated into the current of Ruhmkorff’s 
large induction coil, we must conclude, from the powerful charge of the jar, as proved 
by flashes of light, that within the spectral tube the tension of electricity, before it 
effects its passage, is very high. In this case the electric light is more bright, and of a 
fine colour like that of blue steel. When analyzed by the prism, it shows the spectral 
lines of hydrogen and oxygen, mixed with other spectral lines, among which those of 
sodium and silicium are the brightest. At the same time the interior surface of the 
capillary part of the tube tarnishes. Hence we conclude that the decomposed glass 
partly conducts the current. 
By means of our tubes, therefore, the theoretical conclusions of Dr. Faraday, that 
electricity being merely a peculiar condition of ponderable matter cannot exist without 
it, and cannot move without being carried by it, are confirmed and supported in a 
striking way*. 
9. As soon as the tube encloses perceptible traces of air, the spectral lines resulting 
from the ingredients of the glass entirely disappear. Though the temperature of the 
gas be raised by the passing current to an immense height, nevertheless, on account of 
its great tenuity and the short duration of the discharge, the gas is not able to heat the 
surface of the glass sufficiently to volatilize it. In this case also no spectral lines owing 
to particles starting from the platinum electrodes appear in the capillary part of the 
tube. Those lines are to be seen only near the electrodes, namely, in the aureola 
surrounding the negative pole. 
10. The temperature of the particles of air seized by the weakest electric spark by 
far surpasses the temperature of the hottest obtainable flame. For no flame whatever 
shows the spectral lines of air, which are constantly seen in the spark. In order to raise 
the temperature of the discharge of Ruhmkorff’s induction coil, you may either increase 
the power of the inducing current, or diminish the duration of the induced one. The last 
plan may be found preferable in most cases. The heat excited in a given conductor by 
a current sent through it increases in the ratio of the square of intensity, but decreases in 
the ratio of the duration of the current. Admitting, therefore, that the conductibility 
is not altered by elevation of temperature, and that the quantity of induced electricity 
remains the same, we conclude that the heating-power of the induced current is in the 
inverse ratio of its duration. But the resistance opposed by gases to the passage of 
* Mr. Gassiot has already obtained vacua so nearly perfect as to present an obstacle to electric conduction. 
See Philosophical Transactions for 1859, p. 148. 
