S43& MAGKKTICAT, OBSKKVATIONS. [aPP. N" IX. 



suppose, then, it would appear, tliat the iron bar and 

 tlie steel bar, when iu certain different positions, pos- 

 sessed the same strength of polarity, their deflective 

 power over the magnetic needle being equal. But 

 though their polarities appeared to be similar, their 

 powers of attraction for iron weie different ; each of 

 them, indeed, when presented (in the magnetic meri- 

 dian, and in the same positions as when tlieh- polari- 

 ties were found to be similar,) to a piece of fine iron 

 wire, freed from magnetism, floating on a surface of 

 water, attracted it forward ; but the steel bar was ca- 

 pable of lifting the wu*e when it was sunk in the wa- 

 ter, while the iron bar could not so much as move the 

 smallest fragment of the same. Hence, it would ap- 

 pear, that that property of magnets by which polarity 

 is produced, is not the same as that by which they at- 

 tract iron. In making the above experiments, the 

 iron bar was heated red hot, and allowed to cool gra- 

 dually in the position of the magnetic equator, imme- 

 diately before it was used, by which it was entb'ely 

 freed from a sensible degree of magnetism that it had 

 accidentally acquired. 



2. The combined influence of the iron distributed through 

 all parts of the ship, seems to be concentrated into a kind of 

 magneticyocM,!? of attraction, the principal south pole of which 

 being upward in the northern hemisphere, is probably situa- 

 ted, in general, near the middle of the upper deck, but 

 nearer to the stem than the stern. 



a. Wrought iron having a much greater atti'action for the 

 magnetic needle than cast-iron, the anchors, which 

 usually lie about the bows, possess much more in- 

 fluence over the compass than guns ; hence the focus 

 of attraction lies nearer to the bows than to the stern. 



3. This focus of attraction so influences the compass 

 needle, that it is subject to an anomaly or vai'iation from 



