The Followers of Maxwell. 36li 



have the form of semicircular tubes forming the two halves 

 of a complete circle. Each tube is enlarged at each of 

 its ends, so as to present a front of considerable area to the 

 corresponding front at the end of the other tube. Thus at each 

 end of one diameter of the circle there is a pair of opposing 

 fronts, which are separated from each other by a thin sheet 

 of the elastic solid. 



The disturbance may be originated by forcing an excess of 

 liquid into one of the enlarged ends of one of the cavities. This 

 involves displacing the thin sheet of elastic solid, which 

 separates it from the opposing front of the other cavity, and 

 thus causing a corresponding deficiency of liquid in the enlarged 

 end behind this front. The liquid will then surge backwards 

 and forwards in each cavity between its enlarged ends ; and, 

 the motion being communicated to the elastic solid, vibrations 

 will be generated resembling those which are produced in the 

 aether by a Hertzian oscillator. 



In the latter part of the year 1888 the researches of Hertz* 

 yielded more complete evidence of the similarity of electric 

 waves to light. It was shown that the part of the radiation 

 from an oscillator which was transmitted through an opening in 

 a screen was propagated in a straight line, with diffraction effects. 

 Of the other properties of light, polarization existed in the 

 original radiation, as was evident from the manner in which it 

 was produced ; and polarization in other directions was obtained 

 by passing the waves through a grating of parallel metallic wires ; 

 the component of the electric force parallel to the wires was 

 absorbed, so that in the transmitted beam the electric vibration 

 was at right angles to the wires. This effect obviously resembled 

 the polarization of ordinary light by a plate of tourmaline. 

 Refraction was obtained by passing the radiation through 

 prisms of hard pitch. j- 



* Ann. d. Phys.xxxvi (1889), p. 769; Electric Waves (Englished.), p. 172. 



I 0. J. Lodge and J. L. Ho ward in the same year showed that electric radiation 

 might be refracted and concentrated hy means of large lenses. Cf. Phil. Mag. 

 xxvii (1889), p. 48. 



