Researches in the Theory and Calculus of Operations. 269 



towards each other like two half- waves in opposite phase ; 

 and when they are suffered to meet, they rush together and 

 neutralize each other in annihilation.* 



At first, the superficial atom a of the electric E (fig. 14 



^Examples are, the production of sparks by the collision of flint and steel ; 

 the ignition of tinder by means of the compression syringe ; the electric spark 

 arising from the violent velocity with which the positive and negative elec- 

 tricities rush together, etc. etc. 



In all these impulsions, collisions or frictions, the intensity will necessarily 

 increase or vary from less to more : the faintest encounter liberating a half- 

 atom of electricity, or rather parting the whole atom between the excitor 

 and excitee ; the medium impulsion setting free the entire spherical atom of 

 heat, forming an infinite atom of caloric in temperature zero at the bound- 

 ary; and finally the most intense, yielding the circular plane wave of light. 



A spark also attends the sudden fracture of a crystalline substance ; an 

 atom is divided, and the plane vibration is formed by the rush of side forces 

 at the instant of the rupture. 



When a hard substance is fractured by a blow, a sphere of force is torn 

 through its centre in a plane surface, which gives an instantaneous lateral 

 vibration answering to the definition of the luminiferous wave. 



Whatever the magnitude or number of the separate calorific atoms evolved 

 by one impulsion on B, they will, like so many drops of water, merge into 

 one body or sheet of calorific force, followed by a similar additional sheet 

 from the next impulse, and so on indefinitely. The essential character of 

 force is equable diffusion, radiation or emanation in space. One liberated ca- 

 loric, therefore, expands and dilates into a hemisphere ; its extension increas- 

 ing and intension (intensity) reducing according to relation of the surface to 

 the radius of the sphere. The rapidity of this movement of radiation has been 

 calculated ; and cannot be explained in any better way than by supposing it 

 to consist in the actual progressive motion of the calorific force itself, irre- 

 spective of the intervening gaseous medium. 



A single heated molecule of matter surrounds itself successively with 

 spherical shells of calorific force, which start on their mission into infinite 

 space ; or, when meeting opposition from other radiating bodies, a mutual 

 and warming encounter occurs, ending with friendly reciprocation of ba- 

 lanced exchanges. 



The luminific force (light) necessarily follows the same relations of space 

 in its outgoing. But as the plane waves must oscillate perpendicularly to 

 the different radii of the sphere, we see that in parting from a luminifying 

 centre, the wave-amplitudes on any spherical surface must interfere, and an- 

 nul or otherwise modify certain extents of luminous effect (detected in the 

 lines of Fraunhofer ? and their variations in the spectral analysis). These 

 phenomena have been studied in the plane triangular prism : it might be 

 advantageous to try a circular prism, formed after the thought suggested by 

 Newton's investigation of the colors yielded by reflection and refraction by 

 thin plates. 



