400 MAGNETISM. 



The attractive power of a magnet may be con- 

 siderably improved by hanging a weight to it, 

 which may be gradually increased; and also by 

 keeping it in a proper situation, viz. with its north 

 pole towards the north, and its south pole, conse- 

 quently, towards the south. On the contrary, this 

 power is diminished by an improper situation, and 

 by keeping too small a piece of iron, or no iron at 

 all, appended to it. 



Most probably the magnet attracts iron only ; 

 but when it is considered how universally iron is 

 dispersed throughout nature, it is evident that a 

 vast number of bodies must, on that account, be 

 attracted by the magnet more or less forcibly, in 

 proportion to the quantity and quality of the iron 

 they contain. Indeed it is wonderful to observe, 

 what a small portion of iron will render a body 

 subject to the influence of the magnet. A great 

 many substances are in a very slight degree at- 

 tracted, which contain an exceeding small quan- 

 tity of it, extremely diffused and oxy dated. 



To discover this small degree of attraction, the 

 substances should be placed upon a piece of paper, 

 or a thin shaving of cork, which should be put to 

 float upon water, and then the magnet should be 

 gently approached sideways, to within one-tenth of 

 an inch distance from the substance under trial. 

 The following substances will, in this manner, be 

 found to be in some measure affected by the mag- 

 net, viz. most metallic ores, especially after having 

 been exposed to a fire. Zinc, bismuth, and par- 

 ticularly cobalt, are generally attracted. The 

 emerald, and particularly the garnet, are not only 

 attracted, but frequently acquire permanent mag- 

 netism. The ashes of most animal and vegetable 



