456 
MAGNETO-ELECTRIC CURRENTS. 
ed in rendering a needle magnetic by placing 
it under a piece of glass, or blue ribbon, 
having half its length protected by paper. 
He did not succeed. He made a very delicate 
experiment, by admitting “ a divergent beam 
of light through a hole in the shutter of a 
dark room ; the cone of luminous matter, 
at its apex, was about 1*1 0th of an inch of 
diameter, and a hair, or other filament held 
in it, exhibited the phenomena of diffraction ; 
the colours being received into the eye by a 
lens. Across this beam a silver wire was 
adjusted, and each of its extremities con- 
nected v;ith cups of mercury, which commu- 
nicated with the poles of a voltaic battery. 
It was expected that, if there was any action 
between a magnetic filament and light, some 
derangement would be seen in the diffracted 
fringes, when the current passed ; but none 
such was observable.” He found also, that 
solar light concentrated upon a delicate 
needle, produced no effect, either in the air 
or in vacuum. “ A needle made of watch 
spring, about 4 inches long, which in an 
exhausted receiver, suspended by a filament 
of silk, exhibited no polarity, had one half of 
it exposed to the violet ray, cast by an equi- 
angular prism of flint glass. This ray was 
separated from the others, by passing it 
through a slit in a metallic screen, and half 
the needle shielded by a piece of paper. After 
two hours exposure, it was suspended again 
in the exhausted receiver, but still showed 
no token of polarity ; it was then exposed to 
the other rays successively, with the same 
result*” 
Mr. Boyle found, that a piece of amber 
would become electrified by exposure to a 
sunbeam. Mr. Draper produced the same 
effect on ruby from Ceylon, rolled sapphire, a 
tourmaline, a Brazilian emerald, a topaz, 
and likewise glass. He attributes this to the 
agency of the light, and not to the heat ; be- 
cause, when exposed to the action of heat 
from another source, in the same degree, no 
such consequence followed. 
ELECTRICITY AND MAGNETISM. 
hlETHOD OF DETERMINING THE 
ELECTRICAL CONDUCTIBILITY OF 
SMALL MASSES. — The usual method of 
determining this property in bodies, consists 
in interposing between an electrical somce 
and a metallic wire attached to a sensible 
electroscope, the body whose conductibility is 
to be ascertained. For this purpose, an 
electrical machine, a voltaic or a dry pile is 
employed. Several ingenious apparata have 
also been substituted, Lassaigne recommends 
a modification v/hich he has found to answer. 
To one of the wires of Schweigger’s multi- 
plier, he attaches a small platinum spoon con- 
taining dilute nitric acid ; above this spoon, 
is fixed upon a support, a small glass tube, 
2*3 inches long, and ;19 inch in diameter. A 
wire of red copper curved at one of its extre- 
mities, traverses it for two-thirds of its 
length. To this distance the wire is flatten- 
ed into a spatula, or terminated by a disk. 
To this part of the ware the body to be tried 
is attached It is then touched on the other 
side with the end of the other wire of the 
multiplier, and then the curved portion of the 
copper wire is plunged into the nitric acid. 
If the body placed between the two wires is a 
conductor of electricity, the magnetic needle 
instantly deviates. He has also found, that 
a thermo-electric cylinder is very conve- 
nient ; it is formed, by soldering, end to end, 
two small cylinders, the one of Bismuth, and 
the other of Antimony. When placed in a 
glass tube and slightly heated at the point of 
union, it was placed in contact on one side, 
with one of the wires of a multiplier, and on 
the other, with the substance to be tried, and 
touched at its opposite extremity, with the 
other wire of the multiplier. The results 
werp. similar to those obtained by the first 
method ; Arsenic and Tellurium were found 
to be conductors.^ 
CHEMICAL ACTION OF ELEC- 
TRICAL CURRENTS.— The experiments 
of M. Botto lead to the conclusion, that the 
direction of a magneto-electric current has 
an influence, like that of a hydro-electric cui;- 
rent, upon the facility which it may have in 
passing through the same system of conduct- 
ors. Mr. Faraday has proved, that the dif- 
ferent substances which form a circle, expe- 
rience, in similar circumstances, an equal 
magneto-electric induction, and, conse- 
quently, a tendency to produce the same 
current. Botto has confirmed this fact. 
He disposed a magneto- electric helix, having 
two distinct and equal ends, in such a man- 
ner, that when it was traversed in a contrary 
direction by two currents developed by influ- 
ence, these two currents neutralized them- 
selves. If in the circle, which these currents 
are obliged to traverse, we place a vessel 
filled with acidulated water, and communica- 
ting with the conductors on one side by a 
wire, on the other side by a plate of the same 
metal, the currents are neutralized. But, if 
one of them is made stronger than the other, 
by a change in the number of the spirals in 
the magneto-electric helix, the effect upon 
the galvanometer which results from this 
dilference of intensity, is much more decided, 
when the most powerful current passes into 
the liquid from the wire to the place, than in 
the contrary direction. Hence, it would ap- 
pear, that w'e are to attribute the double 
phenomenon which the same heterogeneous 
circle presents, under the relations of electric 
conductibility, to the difference of chemical 
re-action which accompanies the passage of 
the currents.-f 
ATMOSPHERICAL ELECTRICITY. 
— M. Matteuci has lately made some inter- 
esting experiments upon this subject. 'They 
were conducted, in what is termed in Italy, 
an English wood (that is, one of small extent) 
consisting of Robinia pseudacacia, Platinus 
Occidentalis, Gleditzia iriacanthos, Melia, 8fc. 
The electroscope with which the experiments 
were made consisted of a stem of wood, at 
* Journ. de Cliim. Medic, i. 63r* 
t Bibliotheque Universelle, February, 1835. 
