MAGNETISM 



Fig. 177, the lines being drawn in towards the sphere. The figure 

 represents those on a diametrical plane parallel to the original 

 direction of the field. The total polarity over one hemisphere is 

 equal and opposite to the total polarity over the other hemisphere. 



FIG. 177. 



so that as many lines of induction converge on to one hemisphere 

 as diverge from the other. 



Now imagine that the >pheiv is cut through in a plane perpen- 

 dicular to the central line of induction and that the two halves are 



drawn a very small distance apart. Then we shall have tubes 

 of induction crossing the air gap thus formed, and as many 

 tubes will cross the gap as enter the curved surface of one 

 hemisphere and leave that of the other. For we can draw a closed 

 surface entirely in air closely surrounding either hemi>phere, and 

 the total flux through such a surface is, as we have seen, /.em, or the 



