ENERGY.	51
If nitrogen had more affinity for oxygen it would combine chemically with it, and we should live in an atmosphere of nitrous oxide, or laughing gas.
The molecule, therefore, of nitre-glycerine resembles a house of cards, so nicely balanced that it will just stand, but will fall to pieces at the slightest touch. "When this is supplied by a slight percussion the molecule falls to pieces and is resolved into its constituent atoms, which rush together in accordance with their natural affinities, forming an immense volume of gas, partly of water in the form of steam where oxygen has combined with hydrogen, and partly of carbonic dioxide where it has combined with carbon, leaving the nitrogen atoms to pair off, and revert to their original form of two-atom molecules of nitrogen gas. It is as if ill-assorted couples, who had been united by matrimonial bonds tied by the manoeuvres of Belgravian mothers, found themselves suddenly freed by a decree of divorce a vinculo matrimonii, and rushed impetuously into each other's arms, according to the laws of their respective affinities. So striking is the similitude that one of Goethe's best-known novels, the ' Wahlverwandschaf-tcn/ takes its title from the human play of these chemical reactions. The enormous energy developed when these atomic forces are let loose and a vast volume of gas almost instantaneously created, is attested by the destructive force by which the hardest rocks are shattered to pieces and the strongest buildings overthrown.
These loves and hatreds, or, as they are termed, chemical affinities and repulsions of the atoms, are the principal means by which the material structure of the universe is built up from the original elements. The earth, or solid crust of the planet we iiftiabit, consists