MAGNETIC ATTRACTION. 



37 



tate they all fall to the earth for the force 

 of gravitation never fails. Now, I have here a 

 centre of power which I will not name at present, 

 and when these particles are placed upon it, 

 see what an attraction they have for each other. 

 Here I have an arch of iron filings (fig. 12) 



Fig. 12. 



regularly built up like an iron bridge, because 

 I have put them within a sphere of action which 

 will cause them to attract each other. See ! 

 I could let a mouse run through it, and yet if I 

 try to dp the same thing with them here [on the 

 table] they do not attract each other at all. It 

 is that [the magnet] which makes them hold 

 together. Now, just as these iron particles hold 



D 3 



