112 LIGHT EXCITES ELECTRIC CURRENTS. 



Crookes, as produced by the action of the light 

 and heat of a lamp, as well as by that of sun- 

 shine. 



" Four discs, made of light pith, of the size of 

 a sixpence, balanced on the ends of two straws, 

 are adjusted to revolve horizontally on a pivot. 

 The sides of the pith-discs are inclined downwards. 

 They have one side blackened by plumbago, or 

 lamp-black, and the other side white." The Profes- 

 sor says : " When this apparatus is placed under a 

 bell-glass in a vacuum, it will revolve by the action 

 of sunlight or of a lamp." There appears to be 

 an analogy between the revolutions of this frame 

 and those produced by the lamp in the experiment 

 described. The difference of colors of the discs, 

 black and white, corresponds with the difference of 

 conducting powers of the metals employed in the 

 thermo-electric apparatus ; and their sides sloping 

 downward correspond with the vertical sides of 

 the wire frame. Then, again, the transmission of 

 the vibrations of the all-pervading electric ether is 

 more obvious beneath an exhausted bell-glass, than 

 in the open air; as illustrated by Fig. i, page 23.* 



To determine the different action of terrestrial 

 currents on the vibrations of the electric ether 



1 In a treatise on "Light as a Motive Power," p. 55, by R. H. 

 Armit, R. N., the following explanation is given : " Light has been de- 

 monstrated to be both a repulsive and attractive force. The resultant 

 of these forces, as regards the earth, would therefore be,y?;-j/, to hold the 

 earth grasped within the rays of light, as within a pair of tongs. And, 

 secondly, these tongs being carried round by the sun in his rotary motion, 

 an orbital motion is given to the earth, and to all celestial bodies receiv- 

 ing solar light." 



