140 Radiant Forces. 



original quantity of motion has fco be divided amongst a greater 

 number of particles, and consequently each one will have less. 

 Thus the further the waves are away from the stone, the less 

 will be their height and depth ; or the smaller they will be- 

 come when measured vertically, although they are greater in 

 breadth. 



This water comparison does not, however, afford a complete 

 idea of the propagation of light, because we notice only what 

 takes place at the surface of the water. If a diver exploded a 

 circular mass of gunpowder at a given depth, the water would 

 be struck equally in all directions, and the wave produced 

 would be like a series of spherical shells, one outside the 

 other. Each shell would contain more water particles than the 

 one next to itself and nearer the source of motion, and fewer 

 particles than the one next to it and further from that source. 

 Thus in the spherical waves nearest the explosion the motion 

 of particles would be violent, and it would grow less and less 

 violent as the spherical waves grew wider and wider, as they 

 receded from the centre of explosion. 



A particle of matter becoming luminous acts like the 

 explosion supposed in the case of the water. It communicates 

 a strong wave motion to a spherical shell of the adjacent ether, 

 and the particles of that first shell hand it on to a second, and 

 so on in infinite progression. As long as the waves have force 

 enough to be visible we call them light. If the ether particles 

 have sufficient attraction for each other, the process must go 

 on, as in the case of the water; but is this known to be fact ? 

 Is it certain that the spherical shells of light are continuous 

 and without break in the sense in which spherical water w T aves 

 possess that property ? 



If we consider light as propagated in waves like concen- 

 trated spherical shells, a light ray will consist of the oscillations 

 of all those particles which stand in front of the first moved 

 particle, which acts as their source of motion, by communicating 

 to them its own motion. 



Optical experiments show that one set of light rays may 

 be made to pass through another set without apparent loss. 

 The method of illuminating opaque objects under high powers, 

 originating with Professor Smith, of Kenyon College, as des- 

 cribed in a former number of the Intellectual Observer, and 

 well-known in this country through the contrivances of* Mr. 

 Richard Beck, and Messrs. Powell and Lealand, illustrate this 

 fact. Light rays are sent down through the object-glass on 

 to the object, and then, being reflected by the object, they 

 come back again without jostling one another, so far as can be 

 discerned. But, by another kind of experiment, light waves 

 can be made to interfere with each other, and produce either 



