PHYSIOLOGY OF LIFE. 89 



interpose the same piece of iron lengthways ; in which 

 case the position of the compass needle will be scarcely 

 or not at all affected. 



The assertion of Bernoulli and others, that the abso- 

 lute force of the artificial magnet increases in the ratio 

 of its superficies, stands corrected in the far more accurate 

 experiments of Coulomb (published in his Treatise on 

 Magnetism), which proves that the increase takes place 

 (in a far greater degree) in the ratio of its length. The 

 same naturalist even found means to determine that the 

 directing powers of the needle, which he had measured by 

 Jielp of his balance de torlion, stand to the length of the 

 needle in such a ratio as that, provided only the length of 

 the needle is from forty to fifty times its diameter, the 

 momenta of these directing powers will increase in the 

 very same direct proportion as the length is increased. 

 Nor is this all that may be deduced from the experiment 

 last mentioned. If only the magnet be strong enough, 

 it will show likewise that magnetism seeks the length. 

 The proof is contained in the remarkable fact, that the 

 iron interposed between the magnet and the magnetic 

 needle breadthways constantly acquires its two opposite 

 poles at both ends lengthways. Though the preceding 

 experiments are abundantly sufficient to prove the position, 

 yet the following deserves mention for the beautiful clear- 

 ness of its evidence. If the magnetic power is determined 

 exclusively by length, it is to be expected that it will 

 manifest no force, where the piece of iron is of such a 

 shape that no one dimension predominates. Bring a 

 cube of iron near the magnetic needle and it will not exert 

 the slightest degree of power beyond what belongs to it 



