1821.] | 15 7 ] 
REPORT OF CHEMISTRY AND EXPERIMENTAL PHILOSOPHY, 
-»- 
ROFESSOR LESLIE lias made some 
experiments upon sound excited in 
hydrogen gas ; from which it appeared that 
the effect was considerably less than what 
would be produced in atmospheric air of 
the same density. The cause appeared to 
depend partly on the tenuity of hydrogen 
gas, and partly on the rapidity with which 
the pulsations are conveyed through this 
■very elastic medium. 
The connection between galvanism and 
magnetism has been illustrated by the Rev. 
J. Gumming, professor of chemistry at 
Cambridge. The Professor has repeated the 
electro-magnetic experiments of Professor 
Oersted 3 he gives an account of the effects 
of a wire connecting a large zinc and copper¬ 
plate, on two magnetic needles, one moving 
horizontally, the other vertically 3 the con¬ 
necting wire being bent into the form of a 
circle, and the needles applied to it at dif¬ 
ferent azimuths. The direction of (he gal¬ 
vanic current was such, that a wire con¬ 
necting the zinc and copper-plates tended 
to place itself at right angles to the mag¬ 
netic meridian, which appeared expeii- 
mentally, by suspending a pair of very 
small plates. An instrument was then 
described for detecting weak galvanic ac¬ 
tion, by its effects on the magnetic needle. 
It was found that the magnetic influence 
could not be transmitted between a pair of 
plates through any non-metal lie medium ; 
but, on making the circuit through a tube 
filled with acetate of lead, the needle be¬ 
gan to be effected, when the arborescence 
of the revived lead had formed the metallic 
connection. On using connecting-w ires of 
different lengths and diameters, it appear¬ 
ed that the magnetic influence was trans¬ 
mitted through large wires, though of con¬ 
siderable length, provided they were solid, 
more readily than through small ones, how¬ 
ever short. An analogous effect was found 
to be exhibited on connecting the poles of 
a magnet by pieces of iron, of different 
lengths and thickness. The paper was 
concluded by contrasting this analogy with 
the opposite effects observed in the trans¬ 
mission of common electricity. 
The same gentleman, on the application 
of magnetism as a measure of electricity, 
describes a galvanometer consisting of a 
connecting-wire moveable upon a gra¬ 
duated slide. By comparing the deviations 
of a needle placed below r it at different dis¬ 
tances, the tangent of the deviation was 
found to vary inversely as the distance of 
the connecting-wire from the magnetic 
needle. On applying the deviation pro¬ 
duced on the magnetic needle as a measure 
of the increased effect produced by mov ing 
two galvanic surfaces towards each other, 
it appeared that the tangent of the devia¬ 
tion varied inversely as the square root of 
the distance of the plates from each other. 
A steel-wire was made permanently magne¬ 
tic,by twisting it round a straight connect¬ 
ing-wire. A horse-shoe magnet was placed 
in the circuit, by twisting a wire from right 
to left round one pole, and from left to 
right round the other 3 on connecting it 
alternately with each end of the battery, 
the magnetism of one pole w r as destroyed, 
whilst that of the other was increased. On 
transmitting the galvanism from a pair of 
plates of It feet of surface through a cop¬ 
per globe of four feet surface, the mag¬ 
netic influence was distributed over every 
part, both of the globe and of the plates 
themselves. 
Heat has been discovered in the moon’s 
rays by Dr. Howard, by means of a dif¬ 
ferential thermometer of his own invention. 
Having blackened the upper ball of a dif¬ 
ferential thermometer, he placed it in the 
focus of a 13 inch reflecting mirror, which 
was opposed to the light of a bright full 
moon. The liquid began immediately to 
sink, and in half a minute was depressed 
8 °, where it became stationary. On plac¬ 
ing a skreen betwen the mirror and the 
moon, it rose again to the same level, and 
was again depressed on removing this ob¬ 
stacle. 
Dr. Olbers informs Dr. Gauss, that he 
observed on the 5th of February an appear¬ 
ance in the dark part of the moon, which 
has been called a lunar volcano. It ap¬ 
peared as usual in Aristarchus. Jt was 
small, but much brighter than the other 
parts of the moon, unilluminated by the 
sun, quite like a star, and even appeared 
like a star of the sixth magnitude, seen 
situated to the north-east of the moon. Dr. 
Olbers is inclined to believe that this 
brightness is produced by the reflection of 
the light of the earth from an even and 
smooth surface of a great extent of rock in 
the moon. 
Recent investigations having directed 
the attention of observers in a particular 
manner to the study of the optical charac¬ 
ters of crystallised minerals, we think it 
may not be without use to notice a circum¬ 
stance in the structure of crystals, which, 
if not known, or neglected, may lead into 
error. Many crystals, which, in a ge¬ 
neral view, appear simple, are found to be 
compound, when all their relations are at¬ 
tended to 3 and these, when examined op¬ 
tically, will present a compound, in place 
of a simple structure. The simple struc¬ 
ture characterises the species of minerals, 
while the compound structure otten dis¬ 
tinguishes the varieties or subspecies. 
MM. Akago 
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