SECT. ii. ON MOLECULAR ARRANGEMENT. 91 



instance of the correlation of electricity and heat, and 

 of the power of the cohesive force. 



When electricity is passing through conducting sub- 

 stances or when it is static, it induces an electric state 

 in bodies at a distance by transmission through non- 

 conducting substances or air, for it gives polarity and 

 tension to the adjacent atoms, and these to the next, 

 and the next in succession, throughout the whole inter- 

 vening mass, a strong proof of the individuality and 

 polarity of the atoms of matter. 



Motion, which is the result of all the physical powers, 

 has itself a strong action upon the ultimate elements 

 of matter; in cases of unstable equilibrium it accele- 

 rates and even determines their chemical union. Some 

 substances will remain merely mixed as long as they 

 are at rest, but no sooner is their inertia disturbed by a 

 slight motion than they rush into permanent combina- 

 tion. In newly sublimed iodide of mercury the vibration _>_ 

 impressed by the scratch of a pin is so rapidly trans- 

 mitted through the mass that its colour is immediately 

 changed from yellow to bright red. By a new arrange- 

 ment of the molecules their action on light is altered. 



Catalysis or the chemical decomposition and composi- 

 tion of substances by the contact of a foreign body, is 

 well illustrated by the chloride of nitrogen, that explodes 

 when touched by substances which at ordinary tempera- 

 tures would neither combine with the chlorine nor with 

 the nitrogen. The iodide of nitrogen explodes if 

 touched by a feather, and M. Becquerel decomposed the ^ 

 iodide of nitrogen by the vibrations of sound. When 

 substances only exist in consequence of the inertia of 

 their atoms, the instability of their chemical attractions 

 and repulsions is only increased by an external agent, 

 so that a great effect is produced by a slight cause, as 

 in an avalanche, the snowy mass is on the point of 

 falling, and the smallest motion, a breath of wind, hurls 



