ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 243 



Fig. 172. 



137. Maxwell's mechanical model of the ether. The ether is 

 to be considered as built up of very small cells of two kinds, posi- 

 tive and negative, in such a way that only unlike cells are in 

 contact. These cells are imagined to be gear wheels provided 

 with rubber-like teeth, as shown in Fig. 

 172, so that if a cell be turned while the 

 adjacent cells are kept stationary, then a 

 torque due to elastic distortion of the gear 

 teeth is brought to bear upon the turned 

 cell. 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 at a point in the magnetic field are thought of as ro- 

 tating about axes which are parallel to the direction of the field 

 at the point, the angular velocity of the cells being proportional 

 to the intensity of the field. The positive cells rotate in the di- 

 rection in which a right-handed screw would be 'turned that it 

 might move in the direction of the field, 

 /^p\ (\ (^f) (+) and the negative cells rotate in the oppo- 



(~~) (~~) CD s * te direction. This opposite rotation of 

 (~P) (+) (Q (H) positive and negative cells is mechanic- 



(^\ (^ (x) ally possible since only unlike cells are 

 (~h) (i) &t tD geared together. This rotatory motion 



(^\ \^\ ,OQ< of the ether cells is shown in Fig. 173, 

 which represents a magnetic field perpen- 

 dicular to the plane of the paper and 

 directed away from the reader ; all the positive ceihrarerotating 

 clockwise and all the negative cells are rotating counter-clock- 

 wise. The energy of the magnetic field (see Art. 44) is repre- 

 sented by the kinetic energy of rotation of the ether cells. 



Conception of the electric field. The positive ether cells at a 

 point in an electric field are thought of as being displaced in the 

 direction of the field, while the negative cells are displaced in the 

 opposite direction, and this displacement is assumed to be pro- 



Fig. 173. 



