24 Experimental Philosophy. [Lecture 3. 



who deal in mathematical and philosophical in- 

 struments. Soft iron acquires magnetism with 

 more ease than hard iron or steel, but the latter 

 will retain it much longer. A well tempered bar 

 of steel will retain the magnetic virtue for many 

 years without diminution. 



The magnet which has the strongest power of 

 attraction does not always communicate it most 

 freely to iron or steel. This circumstance has 

 occasioned a distinction between the different 

 kinds of magnet. Those which communicate 

 most freely and in the greatest degree the mag- 

 netic virtue, are called generous; those which 

 raise the greatest weight in proportion to their 

 size, are called vigorous magnets. The magnetic 

 virtue is not diminished, but is rather increased, 

 by communication. Though however it may be 

 communicated by simply touching the bar of 

 iron or steel, yet it is augmented by repeatedly 

 touching or rubbing it with the magnet : but it 

 must be always rubbed one way only, that is, 

 either from left to right, or from right to left ; 

 for if the magnet is drawn backward and forward 

 on the iron the power will be destroyed, for rea- 

 sons that will be hereafter explained, treating of 

 the poles of the magnet. 



The magnetic virtue is found to be the most 

 active at two opposite points of each magnet, 

 which have been termed its poles, from their 

 correspondence with the poles of the earth, as is 

 found by placing the magnet on a small piece of 



