1872.] Electricity. 533 
thick, and is not at all remarkable for the strength of its magnetism. As to 
the cause of the phenomenon, I think it may be attributed to the tendency of 
the flame to rotate on the approach of the magnet. This might cause the 
extinguishing of the light in two ways :—either by the irregularities on the 
surface of the carbon electrodes offering greater resistance to the passage of 
the current from some points than from others, or by the current being unable 
to pass through the greater distance of the arched path, which is always 
assumed by the light on the approach of a magnet. Another assumption, 
which, though perhaps not so simple as those already mentioned, at least as 
probable, is that on the approach of the magnet there is a slight increase in 
the non-conducting power of the medium between the electrodes, produced by 
their polarisation, and which, though always acting, can only manifest itself 
in a striking manner when the distance between the electrodes is near a maxi- 
mum and the tension of the current is exerted to the utmost in passing through 
the non-conducting medium. This assumption of the polarisation of the 
medium between the electrodes and its consequently diminished power of 
conducting the current seems to be somewhat sustained by the fact thata 
powerful electro-magnet, in the form of a horse-shoe, when approached, did not 
extinguish the light, although it produced rotation of the current ; for we may 
conceive that the two poles acting simultaneously on the medium would neu- 
tralise each other’s effects. I noticed, on several occasions, that the south 
pole of the magnet would not extinguish the light until it was approached 
I inch nearer than the north pole, namely, to within 3 inches of the electrodes. 
This, however, may have been accidental.” . 
Sir William Thomson desires to make known the following case, among 
many constantly occurring under his notice, of the employment of inferior 
copper wire in the construction of electrical apparatus. He received lately, 
from a Glasgow bell-hanger, a large quantity of cotton-covered copper wire, 
which was being largely used for the coils of electric bells; and upon having 
it tested very accurately, by means of his new multiple arc conduétivity-box, 
its resistance per metrogramme was found to be no less than 0439 of a B. A. 
unit, that of ordinary good copper wire for such purposes being about 0°16 of 
a B.A. unit. 
M. J. Morin has arranged a new sulphate of copper voltaic element, with 
the view of the application of continuous currents to therapeutic purposes. 
It has for its object the complete avoidance of the inconvenience which re- 
sults, in the ordinary sulphate of copper element, from the deposit of zinc 
either on tlte copper or the porous cell. It consists of a cylinder of copper, 
the interior of which is concentric with the cylinder of zinc; the annular 
space comprised between these two metallic surfaces is divided into two equal 
parts by acylinder of filter-paper. Ordinary sandstone is put between the 
interior surface of the copper and the paper diaphragm, and sublimated sul- 
phur on the side of the zinc ; the whole is plunged into a solution of sulphate 
of copper, which penetrates through the mass, by means of the numerous 
minute orifices, freely to the copper. Some hundred elements prepared in 
this manner, and frequently in use, have been set up for more than twenty 
months, and the alteration which they have undergone shows that this is but 
half the time for which they may be worked: they have been perfe@ly closed 
during this time, and have neither been subjected to repair nor inspection. 
Professor Forster, in a recent number of “ Poggendorff’s Annalen,” gives an 
account of a curious effect observed in a gold-leaf ele@roscope. He was one 
day showing to an audience that if the leaves were ina state of divergence 
through negative electricity, the divergence would be increased on approach 
of a negatively electrified body, and that it would be diminished in the oppo- 
site case. To prove this, he had a magnified image of the leaves projeéted on 
the screen. He rubbed a rod of caoutchouc with cat-skin, and touched with 
it the ball of the ele@roscope. On removing the rod the leaves showed about 
70° divergence. He again rubbed the rod, and brought from above towards 
the electroscope, the axis of the former being at right angles to the vertical 
axis of the latter. Expecting the divergence to increase, he was surprised to 
