246 



ADVANCED ELECTRICITY AND MAGNETISM. 



Fig. 187. 



ideas of electromagnetic action. Maxwell was the first to work 

 out such mechanical ideas, and Maxwell's conceptions are made 

 use of in the following discussion. Everything in this discussion 

 refers strictly to two dimensions; certain inconsistencies arise 

 in the attempt to extend these conceptions to three dimensions. 



Maxwell's model of the ether. The ether is to be considered 

 as built up of very small cells of two kinds, positive cells and 

 negative cells, in such a way that only un- 

 like cells are in contact. These cells are 

 imagined to be gear wheels provided with 

 rubber-like teeth so that if a cell be turned 

 while the adjacent cells are kept station- 

 ary a torque due to the elastic distortion 

 of the gear teeth is brought to bear upon 

 the turned cell. Figure 187 shows five 

 positive cells and four negative cells geared 

 together in the manner specified. In subsequent figures, these 

 cells or cog-wheels are represented by plain circles for the sake 

 of simplicity. 



Conception of the magnetic field. The ether cells in a mag- 

 netic field are thought of as rotating about axes which are 

 parallel to the direction of the magnetic ^=z< s?=* ^ ^ 

 field at the point, the angular velocity ^/^Vf^ 

 of the cells being proportional to the in- /2\*Y5v*fr^V(^ 

 tensity of the field. The positive cells ^ 

 rotate in the direction in which a right- / 

 handed screw would be turned that it 

 might travel in the direction of the field, 

 and the negative cells rotate in the oppo- 

 site direction. This opposite rotation of positive and negative 

 cells is mechanically possible because unlike cells only are geared 

 together. Thus, in Fig. 188, the positive cells are represented as 

 rotating in a clock-wise direction, and the negative cells as 

 rotating in a counter-clockwise direction; this is a state of motion 



Fig. 188. 



