22 MR. p. BARLOW'S INVESTIGATION OF THE 



gun-carriages of the same material. When the late Arctic 

 Expeditions were first in contemplation, the local attraction of 

 the vessels in those seas was one of the objects to which the 

 attention of the officers was particularly directed. The re- 

 sults of the experiments made in these instances, are given by 

 Captains Ross and Parry in the accounts of their respective 

 voyages; and the amount of the disturbing force was found to 

 be such, as to call for some prompt and efficient remedy ; the 

 difference of bearing of an object having been found by Cap- 

 tain Sabine to be at least 50, or nearly 4-f points of the com- 

 pass, merely from a change of position of the ship's head from 

 east to west ; so that while the compass indicated the vessel 

 to be sailing due east, she might in reality be proceeding due 

 north-east. 



It is true that seamen depend very little upon the reckoning 

 by compass, while they can make the requisite astronomical 

 observations ; but as it frequently happens that many days 

 may pass without their obtaining such observations, it could not 

 but be of considerable importance to them, in such cases, to 

 possess the means of making the nearest possible approxima- 

 tion to their true place. It is not in the open sea, however, that 

 the compass, at the present time, is of the greatest use ; it is in 

 the navigation of narrow channels, in piloting ships by means 

 of charts and bearings, and in marine surveying, that it finds 

 its most valuable application : in these instances nothing can 

 supply the place of the compass, and it was manifestly impor- 

 tant, in such cases, that its directive power should be freed from 

 all irregularity. Every reader, whether a nautical man or not, 

 must be aware of the great amount of error, and fatal conse- 

 quences, which might arise in a few hours to a vessel in the 

 Channel, in a dark and blowing night, having for its only guide 

 a compass subject to an error of 14 in opposite directions 

 at east and west, (which was actually the case, from the ef- 

 fects of local attraction, with the Griper, when at the Nore,) 

 the very courses on which she would be endeavouring to 

 steer ; " and who can say," Mr. Barlow himself observes, 

 "how many of the mysterious wrecks which have taken place 

 in the Channel are to be attributed to this source of error, of 

 which the most recent, that of the Thames, Indiaman, is a 

 serious example. This vessel, besides the usual materials, 

 guns, &c. had a cargo of more than 400 tons of iron and steel; 

 and it may easily be imagined that such a cargo would pro- 

 duce an effect on the compass at least equal to [that of the iron 

 in] the Griper and Barracauta [another ship on which expe- 

 riments were made] ; and this alone would be quite sufficient 

 to account for the otherwise unaccountable circumstance, that 



