1823.] Analyses of Books. 453 



Article XI. 



Analyses of Books. 



An Essay on Magnetic Attractions, and on the Laivs of Terres- 

 trial and Electro-Magnetism, %c. By Peter Barlow, Associate 

 in the Society of Civil Engineers, and of the Royal Military 

 Academy. Second Edition, much enlarged and improved. 



We have to apologize to Prof. Barlow, and to our readers, for 

 our tardiness in noticing this much improved edition of his 

 work ; but we shall now endeavour to compensate for the delay, 

 by giving a more complete account of it than various circum- 

 stances, which it is unnecessary to particularize, would have 

 permitted us to have done at an earlier period. 



The leading object of this edition, as of the former one, 

 although a considerable portion of the work is devoted to elec- 

 tromagnetism, is the developement of the mathematical princi- 

 ples of magnetism, and their application to the correction of the 

 local attraction of vessels, " which is of more and more import- 

 ance," the author remarks, in the preface, " as every year is 

 leading to some new application of iron in the construction and 

 equipment of ships of war, and which, if persevered in without 

 some mode of correction, would soon render the compass worse 

 than useless as a nautical instrument." 



" It may be observed, for example," he continues, " that 

 besides there being at present considerably more iron ballast 

 than formerly, the water-casks are now replaced by iron tanks 

 presenting an immense attracting surface ; iron knees, sleepers, 

 plates, and, in some cases, the riders, have been introduced m 

 lieu of those of timber ; even the hempen cables have been put 

 hors de service by the patent cables of iron,— gun-carriages of 

 this metal are at this moment supplanting those of the usual 

 material : the ingenious patent capstan of Captain Phillips, 

 which will doubtless soon become generally applied, is princi- 

 pally of iron ; and, although of no considerable mass, is so 

 situated as to affect the compass very sensibly; and, lastly, it 

 seems probable that even the masts are to be attempted in this 



material." 



The work is now divided into three parts ; tne first contain- 

 ing the greater portion of the matter constituting the former 

 edition, of which some account was given in the Annals, O. S. 

 vol. xvi.p. 294—307, with the addition of some experiments on 

 the local attraction of vessels, which, by the favour of the Lords 

 of the Admiralty, the author has been enabled to make on board 

 several of his Majesty's vessels, and of the results on the same 

 subject obtained by a series of observations in his Majesty s 

 ship Leven, during a voyage to, and survey of, the western 

 coast of Africa. Prof. Barlow has also appended to this dm- 



