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Art. XVI .—Account of the Electro-Magnetic Apparatus of 
Lieut.-Col. Offerhaus. By G. Moll, A. L. M. Phil. Doct. 
Member of the Royal Institute of the Netherlands, and Pro- 
fessor of N atural Philosophy in the U niver sity of U trecht . I n 
a Letter to Dr Brewster. 
Sir, 
A s soon as Dr Oersted’s experiments were known in this 
country, I set about repeating them with my friend Mr Van 
Seek. We first employed a trough apparatus of 120 zinc four 
inch plates, each zinc plate being placed between two copper 
ones. The apparatus is the same as described in Mr Brande’s 
Chemistry. Though the effect of this Voltaic battery was as 
strong as could be expected from its size, it did not act on the 
magnetic needle with the force which we anticipated, the devia- 
tion being only 14°, even with a strongly impregnated needle. 
We then had an apparatus constructed, consisting of a copper 
trough, as narrow as conveniently could be made, but long, and 
deep enough to contain a zinc plate of 3600 square decimeters. 
The zinc was kept separate from the copper by wooden tarsels, 
and the space between the two metals was filled up with water, 
containing ^th of its weight of nitric, and another / s th of sul- 
phuric acid. A wire projected from the zinc, and another from 
the copper, and on these two a conjunctive horizontal copper 
wire was laid, so as to be placed in the magnetic meridian. Un- 
der this the magnetic needle was put. I believe this apparatus 
was the same winch Dr Oersted recommends. I presume ours 
was larger than his ; but I cannot ascertain this fact, as I have 
not Dr Oersted’s paper at hand. This voltaic battery did not 
decompose a single drop of water, nor could I perceive any 
other chemical effect. Its copper pole was positively electrified ; 
its zinc pole negatively, contrary to what is observed in other 
galvanic apparatuses. Its magnetic power in impregnating 
needles, suspended in spirals between the wires attached to each 
pole, was very powerful. The deviation of the magnetic needle, 
placed under or above its conductive wire, was much stronger 
than the ordinary trough apparatus. But it is unnecessa- 
ry to trouble you further with an account of experiments 
