BEHAVIOUR OF PERMANENT MAGNETS. 739 



duction. Sometimes pieces of this ore, which are 

 already magnetic, are found in mines ; they are called 

 'natural magnets' (or 'lodestones '). These magnets 

 as well as ' artificial magnets/ produced by rubbing 

 steel with natural magnets, were known long before the 

 discovery of galvanic electricity and of the connection 

 between electricity and magnetism. 



That a freely suspended magnet takes up a definite 

 direction may be observed by means of a small magne- 

 tised bar of steel, suspended by means of a stirrup made 

 of paper and a fine (untwisted) thread, as shown in 



FIG. 37*3 (an.proj.; real size). 



fig. 373; or a 'magnetic needle,' that is, a small flat 

 piece of steel pointed at the ends so as to be lozenge - 

 shaped, is provided with a small cap by which it can be 

 placed upon the point of a pin as a pivot about which 

 it is freely movable. 



The little cap, a section' of which is shown at B in fig: 374^ con- 

 sists usually of a small hollow cup of brass, closed at one side by a 

 piece of agate on the lower side of which there is a shallow conical 

 cavity ; when the cavity is placed 011 the point, the needle is 

 balanced in a horizontal position. The magnetic needles sold by the 

 dealers, are often tempered blue and afterwards repolished at one 

 end so as to distinguish the poles. In. the experiments on magnetic 

 attraction and repulsion, in order to know which poles are under ob- 

 servation, one end of the magnet may be marked by pasting a bit 

 of paper upon it or coating the end with sealing-wax varnish. 



3 B 2 



