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LXXI. On the Distribution of the Magnetic Fluids in Masset 

 of Iron: and on the Deviations tvhich they produce in Com- 

 passes placed within their Influence. By Mr, Charles 



BONNYCASTf-E. 



AT having been observed by modern navigators, that the iron 

 which enters so largely into the construction and equipment of their 

 vessels, is capable of producing a very sensible effect upon the 

 needle ; much attention has lately been turned towards explain- 

 ing and correcting the error thus produced. With this view, 

 Mr. Barlow of the Royal Military Academy, Woolwich, has, not 

 long since, published a Memoir, containing the results of a nu- 

 merous set of experiments, made principally upon spheres of iron : 

 and a few pages on this subject have also been written by Dr. 

 Young, and printed by order of the Board of Longitude. 



The latter of these productions, from its nature and the as- 

 sumptions on which its investigations are founded, can only be 

 considered as affording a probable approximation to the truth ; 

 and the former, independently of its impeaching in some degree 

 the received theory of magnetism, is professedly experimental; 

 and for this reason requires some further evidence to prove that 

 the conclusions of its author, drawn as they are from a restrit.:ted 

 case, may be safely employed under the variously modified ac- 

 tions which arise from the irregularity of the ferruginous masses 

 contained in a ship, and the alterations in the intensities and di- 

 rections of the magnetic fluids, which take place with every 

 change of position on the surface of the globe. 



To remove these difficulties, and to investigate from the theory 

 of Coulomb the magnetic attractions of masses of iron of all 

 figures, and for all places, is the object of the following pages : 

 in which if I have succeeded, I flatter myself I shall have added 

 something to the stability of the theory I have employed, by 

 showing how ready an explanation it affords of many magnetic 

 phaenomena, to the investigation of which it has hitherto been 

 applied without success*. 



The principle upon which it is my intention to found this in- 

 quiry, is an extension of the law that regulates the action of elec- 



• Mr. Barlow, although led by his results to entertain some doubts of 

 Coulomb's theoiT, has observed, " If therefore, when the mass of iron is 

 great, and the distance at whicii it acts considerable, the laws which I have 

 developed should be found to be the necessary consequence of the hypo- 

 thesis to which I have alluded, (Coulomb's,) the agreement will furnish 

 one of the best proofs that has yet been given of t'le accuracy of the de- 

 ductions upon which that hypothesis is founded ; and, I should hope, witli- 

 out detracting in any manner from the value of the experimental results de- 

 tailed in the foregoing pages of this work, — (Essay on Magnetic Attrac- 

 tions, page 121.) 



trifled 



