90 ELEMENTARY LESSONS ON [CHAP. n. 



lightly tapped. The figures thus obtained can be fixed 

 permanently by several processes. The best of these 

 consists in employing a sheet of glass which has been 

 previously gummed and dried, instead of the sheet of 

 paper ; after this has been placed above the magnet the 

 filings are sifted evenly over the surface, and then the 

 glass is tapped ; then a jet of steam is caused to play 

 gently above the sheet, softening the surface of the gum, 

 which, as it hardens, fixes the filings in their places. In- 



Fig. 50. 



spection of the figure will show that the lines diverge 

 nearly radially from each pole, and curve round to meet 

 these from the opposite pole. Faraday, who made a 

 great use of this method of investigating the distribution 

 of magnetism in various " fields," gave to the lines the 

 name of lines of force. They represent, since they 

 are made up of little magnetic particles which set them- 

 selves thus in obedience to the attractions and repulsions 



