Account of PoggendorfTs Galvano-Mag netic Condenser . 113 
magnetism, and will, we are persuaded, lead to a more per- 
fect knowledge of the nature and formation of natural and 
artificial magnets. A spiral apparatus of a different kind, but 
suggested probably by Ampere’s instruments, has been re- 
cently invented by M. Poggendorff of Berlin, and has receiv- 
ed the name of a Galvano-Magnetic Condenser. Through 
the kindness of Dr G. Forchhammer, an able Danish chemist, 
who has spent a few days in our metropolis, on his way to 
examine the statistics and mineralogy of the Faroe Islands, 
we have been enabled to present a notice of it to our read- 
ers, as contained in a letter which he has recently received 
from Professor Oersted of Copenhagen. 
The Galvano-Magnetic Condenser is represented in Plate I. 
Fig. 16, where abed is a spiral wire, having between 30 and 
40 spires. This wire is covered over with silk thread, (in the 
same manner as the strings of a harpsichord are, with brass wire,) 
and one end of it a, for example, is placed in contact with a zinc 
plate, while the other end of it d, is placed in contact with cop- 
per. The zinc and copper plates are each in contact with a 
humid body, such as dilute nitric acid, &c. When the apparatus 
thus prepared is established vertically, as in the figure, and an 
unmagnetised needle m n, supported upon a stand S, is placed 
in the axis of the spiral, it will become magnetical, and will ar- 
range itself in the magnetic meridian. M. Oersted remarks, that 
the unmagnetised needle is in this case a much more delicate 
test of galvanic action/ than even a frog itself. D. B. 
Art. XVI II. — History of Mechanical Inventions and Pro- 
cesses in the Useful Arts. 
— “ The seat of the Useful Arts, — of those which mankind bless, and by which 
they are blessed, — of those which the heart reveres, and the understanding ap- 
proves, is Britain.” — Edin. Rev. Vol. xxxii. p. 388. 
* 
rjn 
1 HOSE who wish to form a correct estimate of the compara- 
tive extent and resources of British industry, must gather their 
information from a visit to foreign countries, and decide upon 
the evidence of their own personal enquiries. Accustomed as 
VOL. V. NO. 9. JULY 1821. H 
