The Sun.
London, England, 1850-05-23 00:00:00

SOCIETY OF ARTS.

The twentieth_ordinary meeting of the session was
held last evening at the society's rooms. The
.Eneet-
ing was numerously attended; Mr. F. Cooke, vice-
president in the chair.
Mr. ROBERT HUNT delivered an interesting lecture
on the application of electro-magnetism as a motive
power. After briefly describing the various disco-
veries made and experiments tried in electro-mag-
netism, both in this country and on the Continent, and
more especially the great series of experiments con-
ducted, by command of the Emperor of Russia, by
Professor Jacobi, at St. Petersburg, and which had
been abandoned after an expenditure of more than
30,0001., Mr. Hunt proceeded to state that the reason
of his having been asked to deliver a lecture on this
subject originated in an opinion which he had
expressed in that room on a former evening, to the
effect that the attempts made in the present state of
He
sm as a the science to employ electro-magnetism
mo-
tive power would end in failure. then described
in a highly interesting manner the mode by which
the electro-motive force is produced, and the laws by
which its action is governed. Among the grounds
which induced him to think that .this mysterious
agency must fail in practice as a motive power, were
the following :—The magnetic
cording to distance,aso lbs.,
of o theg
withoo re
greatest rapidity. Thus,
w
when the forcewithtnhee armature in
contact, it was, at a distance 250th• part of
an inch, only capable of sustaining 90 lbs. ; at the
84th part of an inch 47 lbs., at the 60th part of an
inch 40 lbs., and at the 50th part of an inch, which
would be a necessary distance for any practical pur-
pose, it was but 36 lbs. Again, the tumeent motion
was communicated the power was reduced from
2,232 to 920, or more than one-half. Thus, when
they got a weight of 80 lbs. raised by the de-
composition of one grain of zinc, th.y could
only raise 40 lbs. by the same waste when tht,
magnet became rotary. This he thought was caused
by the secondary or induced current moving in a
contrary direction to the primary current. lie con-
sidered great intensity of action necessary, even it,
point of economy, to produce strong motive power.
Thus, with Groves' battery, which is the strongest,
one-horse power for 24 ti,airs was theoretically ob-
tained with 451hs. of zinc, wh.4eas, in Daniel's bat-
tery, which is more constant nod durable, the satin,
power requires the d,,struction of 75Th;. of zinc. A
grain of zinc raises 801b3. a foot high, while a grain
of coal in a Cornish steam-engine raises 1431b5. the
1 same height. On the other hand, a hundred weight

7

Tests 216 d., while a hundred 'weight of coal
; and when to this was added the reduc-
ion of power in eiectro magnetis'in the moment mo-
tion commenced, he had no hesitation in saying that
the cost of tha latter as a motive power would be
Trom 150 to 200 timrs as great as that of ateeru
power.

- An interesting conversation-ensued, after which the
thanks of the society were voted to Mr. Hunt, and
the meeting separated.

A series of lectures on the chemistry of+
ROYAL POLYTECHNIC INSTITU ,roN.
rogen,
with special reference to its application for conveying
by balloons pyrotechnic and other signals to Sir John
Franklin, has been just commenced by. Mr. Pepper,
chemical professor at the institution. After corn ,
meriting on the present doubtful position of the
Arctic Expedition, the audience was incortned
that it es as not a lecture on amostation, the ohjeet of
the lecture being to introduce ceresie lege 'done
signals invented by Mr. Derby, e f Regent s'reet,
I, imbeth, which the balloons were to carry. The
materials and construction of the balloons were first
noticed; as they might be made of oiled silk, gold-
heater's skin, or prepered paper, the latter was pre-
ferred, because with ordinary care it lasted very well,
and had the great additional advantage of cheapm•g:,.
A five-feet gold-heater's skin balloon cost la, whilst
a dozen paper ones could be mide for 31. 16e ; thus
the number of balloons to be sent might be increased,
and the chances multiplied of some cf the signals
finding their wey to the missing expedition. The
chemical nature of hydrogen was then demonstrated
by various experiments, and its extraordinary light-
ness shown by comparison with coal gas. A tive•tiret
balloon was now sent up with Darby's petards or
shells,-which are attached to a fuse or quick match
lined
.toi tithe, and yield a report directly they touch
the ground equal to a 6-pounder cannon, one being
dropped every quarter of an hour. The bill-distri-
butor, -to which so many aeronauts lay claim, was
next shown, being printed bills which are to be
scattered as the balloons travel over the range of
country. The land and water signals next claimed
attention, being composed of gutta percha car, and
cork, and standing erect on earth or'water, and can
be seen at a distance of two miles by an ordinary
telescope, and would be more likely to attract atten-
tion than the little paper slips. The buoy signals, to
be used in case of distress by the searching party
—the pyrotechnic signals by parachutes—the rocket
signahe-and Darby s arrangements for firing, are all
clearly explained. The structure of the fuse or quick
match employed, and its admirable principle (the
argand), was likewise demonstrated ; and it was shown
that it -would burn just as well for a few minutes as
for several consecutive hours. Many of the balloons
are on the plan adopted by Mr. Shepherd, to commu-
nicate with missing voyagers in the arctic regions.
The numerous experiments exhibited by Mr. Pepper
were admirably done, illustrating his discourse in a
popular -and instructive manner. The lecturer was
greatly applauded at the conclusion of his discourse.