<>0 MAGNETISM. 



greater number of magnetic poles, which will correctly explain the 

 direction of the needle in every part of the earth's surface, yet the 

 dip may he determined with tolerable accuracy, from the snj 

 lion of a small magnet placed at the centre of the earth, and directed 

 towards a point in Baffin's Bay, about 75 north latitude, and 70 

 longitude west of London ; and the variation of the dip is so incon- 

 siderable, that a very slow change of the position of this supposed 

 magnet would probably be sufficient to produce it ; but the opera- 

 tion of such a magnet, according to the general laws of the forces 

 concerned, could not possibly account for the very irregular dispo. 

 sitionof the curves indicating the degree of variation or declination; 

 a general idea of these might perhaps be obtained from the supposi- 

 tion of two magnetic poles situated in a line considerably distant from 

 the centre of the earth ; but this hypothesis is by no means sufficiently 

 accurate to allow us to place any dependence on it. 



The art of making magnets consists in a proper application of the 

 attractions and repulsions of the magnetic fluid, by means of the 

 different conducting powers of different kinds of iron and steel, to 

 the production and preservation of such a distribution of the fluid 

 in a magnet, as is the best fitted to the exhibition of its peculiar 

 properties. 



We may begin with any bar of iron that has long stood in a ver- 

 tical position; but it is more common to employ an artificial magnet 

 of greater strength. When one pole of such a magnet touches the 

 end of a bar of hard iron or steel ; that end assumes in some degree 

 the opposite character, and the opposite end the same character : 

 but in drawing the pole along the bar, the first end becomes neutral, 

 and afterwards has the opposite polarity ; while the second end has 

 its force at first a little increased, then becomes neutral, and after- 

 wards is opposite to what it first was. When the operation is re- 

 peated, the effect is at first in some measure destroyed, and it is 

 difficult to understand why the repetition adds materially to the ine- 

 quality of the distribution of the fluid ; but the fact is certain, and 

 the strength of the new magnet is for some time increased at each 

 stroke, until it has acquired all that it is capable of receiving. Seve. 

 ral magnets, made in this manner, may be placed side by side, and 

 each of them being nearly equal in strength to the first, the whole 

 collf( (inn \\ill produce together a much stronger effect ; and in this 

 manner we may obtain from a weak magnet others continually 

 stronger, until we arrive at the greatest degree of polarity of which 



