132 Nalice<! respecl'i/ig New Books. 



the vessel answers the purpose of a lens of considerable powey 

 Sjnd perfection, at the same time that it admits light in any quan- 

 tity or direction to illuminate the object; and, what is of the 

 utmost importance, a preparation of the greatest delicacy may 

 thus be handed round a class in safetv. 



XVIII. Notices respecthig New Books. 



An Essay q?i Magnetic Attractions : particularly as respects 

 the Deviation of the Conipais an Shipboard, occasiontd hy 

 the local InjJmnce of the Guns, &'c. IVilh an easy practical 

 Method of observing the same in all Parts of the iP'orld. By 

 Peter Barlow, of the Royal Military Academy. Svo. pp. 187, 

 with a Plate. Price 6s-. ^d. 



A HE great practical importance of the subject investigated by 

 the author, and the happy result that has flowed from his assi- 

 duous labours, may be partiv understood from the foUowine sketch 

 of the contents of this valuable little work; but its full merit* 

 can be fully appreciated only by a careful perusal of the essay 

 itself, in which the results of numerous laborious experiments, 

 conducted with much judgement, care and patience, are con- 

 densed in tabular forms. 



Remarks on the Magnetic Experiments recently published ly 



Mr. Barlow in his Essay on Magnetic Attractions, &'c. 



In No. 2.)S of the Philosophical Magazine are given two pa- 

 pers from the Philosophical Transactions on the subject of local 

 attraction : tlie one by W. Scoresby jun. Esq., and the other by 

 Captain Sabine: the latter containing the observations made on 

 board II. M. SS. Isabella and Alexander, in their late voyage in 

 search of a North-west Passage. 



The great importance of this error in practical navigation is 

 placed in a very conspicuous point of view by Mr. Bain in his 

 valuable little treatise on the " Variation of the Compass," and 

 the two papers above referred to fully corroborate the statements 

 of that author. It appears indeed from the observations of Cap- 

 tain Saiiine, that in certain high latitudes, the deviation arising 

 from this cause becomes immenselv great, amounting in some 

 cases to at least half a quadrant. 



Mr. Bain is of the opinion, and lew will he disposed to say it 

 is ill founded, that many of the distressing losses frequently expe- 

 rienced at sea are owing to this source of error : he shows in fact, 

 that in consequence of local attraction, a vessel in our own lati- 



titudes 



