344 Mr Barlow'^s Discoveries in Magnetism. 
white enamel is thus produced, which appears as refractory to 
steel as the original stone, and cannot easily be distinguished 
from a natural lamina of white, when used, as it has sometimes 
been, for producing flat specimens for cameos. By either of 
these modes, indeed, stones for engravers’ work are easily form- 
ed, but in the method of blackening the susceptible lamina by 
sulphuric acid and oil, the effect is more brilliant, and the con- 
trast of the black and white more decided. 
Banff, July 1819. 
Art. XX . — Account of some important discovei'ies in Magic- 
tism^ recently made hy P. Barlow, Esq. one of the Pro- 
fessors of Mathematics in the Royal Military Academy, 
Woolwich^. 
The Treatise on the Variation of the Compass, lately pub- 
lished by Mr Bain, and the magnetical observations made by 
Captain Ross and Captain Sabine, in the Arctic Regions, have 
turned the attention of men of science to the deviation produced 
by the action of the ship upon the needle of the compass. That 
eminent mathematician Dr Thomas Young, has constructed a for- 
mula and a table from the experiments made on board the Isa- 
bella, by which an approximate measure of the deviation may be 
obtained. Lieutenant Robertson of the Isabella, has also deduced 
general rules for the same purpose, and Mr Barlow, in inves- 
tigating the subject experimentally, has been led to several in- 
teresting and important results, which could not have been an- 
ticipated from the known laws of the distribution of magnetism. 
At the commencement of this inquiry, his intention was to 
avail himself of the favourable opportunity furnished by the 
immense masses of iron contained in the Royal Arsenal at 
Woolwich, to make some experiments, with a view of sub- 
* Through the kindness of one of our correspondents, who has seen Mr Bar- 
low’s experiments, and from other sources of information, we are enabled to pre- 
sent our readers with this early notice of them. Mr Barlow’s paper was read at 
the Royal Society on the 20th May 1818, and will probably appear in the next 
part of the Transactions of that distinguished body. — Ed. 
