356 Captain HalFs Notice of a Vmjage of Research. 



lowance of 2 points westerly variation, he conceives his course 

 made good to be NNE. while in fact it is J point more to the 

 eastward, in consequence of the north end of the needle being 

 drawn, as formerly, towards the ship'^s head, the effect of which 

 would of course now be to diminish the westerly variation, just 

 as much as the same cause acting in the opposite direction had 

 augmented the variation, when the vessel's head was directed to 

 the SW, Therefore, in this case, namely, with the vessel's head 

 to the NE., the real course would be \ point more to the east- 

 ward than the navigator would allow for ; and he would, as be- 

 fore, naturally ascribe the difference between his position by 

 dead reckoning, and that by his chronometer, to a current set- 

 ting to the eastward. I have never read or heard of any cur- 

 rent setting towards the Straits of Gibraltar from the Atlantic 

 which this theory would not fully explain. Certainly, however^ 

 an exact account of such undoubted currents as the Gulf Stream 

 along the coast of North America, and that off the Cape of Good 

 Hope, would be useful and interesting. Captain Sabine's re- 

 searches in this respect have already given us some valuable in- 

 formation as to currents near the Equator. 



A very useful branch of this class of subjects would be the 

 measurement of the perpendicular rise and fall of the tides in 

 harbours much frequented by shipping, and also the direction 

 of the stream ; both practical points of considerable moment, but 

 which in most cases are known only to the pilots and fishermen 

 of the spot, although there is no reason why it should not be 

 known to strangers. 



These seem the principal points under the first head of in- 

 quiry ; but there are many others to which an officer having 

 such objects constantly and exclusively in view, would of cout'se 

 direct his attention. 



NAUTICAL SCIENCE. 



Under tliis topic might be classed observations, such as those 

 recently made by Lieutenant Foster at Port Bowen, on atmo- 

 spherical refraction, the dip of the needle, and the diurnal va- 

 riation of the magnet. Astronomical observations on the op- 

 positions of the planets, occultations of the fixed stars by the 

 moon, under favourable circumstances, and various other celes-^ 

 tial phenomena, might be made to good purpose. Correspon- 



