Captain HalFs Notice of a Voyage of Research. S55 



scribed in most books of navigation ; and with respect to the 

 winds in high latitudes, nothing accurate is recorded ; or if re- 

 corded, is not put into that shape which is best suited to the 

 comprehension of sailors. The whole of this apparently complex 

 subject might perhaps be treated in a manner applicable to 

 practice, thereby rendering almost all extensive voyages more 

 expeditious and certain. 



The mysterious subject of currents, though it may not differ 

 essentially in its nature from that of the winds, differs materially 

 from it in practical operation. Not one current in ten marked 

 on our cliarts has any existence ; and the chief office of these 

 investigations would be the negative but useful one of removing 

 such misstatements entirely. There can be no doubt, at all 

 events, that the much-talked of current in the east of the At- 

 lantic is imaginary, and that a behef of its existence arose en- 

 tirely from the local attraction of the needle : it vanishes entire- 

 ly the instant Professor Barlow's correcting plate is affixed to 

 the steering-compass, and returns again whenever the plate is re- 

 moved. 



It may not be uninteresting to state how this curious effect 

 is produced. The local attraction, which is the technical name 

 given to the influence which the iron distributed over the hull 

 exerts upon the needle of the compass, has, in most ships, the 

 effect of drawing its north end forward, or towards the head of 

 the vessel. In the southern hemisphere the reverse takes 

 place. To shew how this produces an apparent current, 

 let it be supposed that a ship steers from the British Channel 

 towards Madeira on a SW. course, by compass, and that the 

 navigator, guided by the best documents in his possession, al- 

 lows two points westerly variation, it is clear he will suppose 

 that his course made good is SSW. But, owing to the local 

 attraction, the north end of the needle has been drawn, we shall 

 suppose, half a point more to the westward, so that in strictness 

 the variation allowed ought to have been 2^ points instead of 2. 

 Thus, the course made good has in fact been S. by W. J W. 

 instead of SSW. ; and the difference of longitude between the 

 dead reckoning and that shewn by chronometers, he natu- 

 rally ascribes to a current setting to the eastward, towards the 

 Straits of Gibraltar. On the return, that is to say, when he is 

 steering by compass NE., and when, by making the same al- 



