170 JAMES CLERK MAXWELL 



pressure throughout is that which wo know actually 

 to exist in the magnetic field. 



According to this hypothesis, then, a permanent 

 bar magnet has the power of setting tho medium 

 round it into continuous molecular rotation about tho 

 lines of force as axes. The molecules which are net 

 in rotation we may consider as spherical, or nearly 

 spherical, cells filled with a fluid, or an clastic solid 

 substance, and surrounded by a kind of membrane, or 

 sack, holding the contents together. 



So far the model does not give any account of 

 electrical actions which go on in tho magnetic field. 



The energy is wholly rotational, and tho forces 

 wholly magnetic. 



Consider, however, any two contiguous strings of 

 molecules. Let them cut tho paper as shown in tho 

 two circles in Fig. 1 : 



Then these cells are both rotating in tho same 

 direction, hence at A, "where they touch, their points of 

 contact will be moving in opposite direct ions, as shown 

 by the arrow heads, and it is diiijrult to imagine how 

 such motion can continue; it would require the sur- 

 faces of the cells to be perfectly smooth, and if this 

 were so they would lose the power of transmitting 

 action from one cell to the next. 



The cells A and 13 may be compared to two cog- 



