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 1 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 discoveries in Magne- 

 tism, recently made by P. BARLOW, Esq. one of the Pro- 

 fessors of Mathematics in the Royal Military Academy, 

 Woolwich *. 



JL HE 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. 



