It is particularly deserving notice, that, after the creation of caloric, the atmosphere was the next regular production. If heat had not previously existed, could the atmosphere have been formed? The Creator, having first impressed certain principles on matter, impregnating it with repelling forces and systematical attractions, proceeded with his work according to these radical and fixed laws. One of the general laws discovered by Dr. Black, and which is laid down as a chemical axiom, is, that “Whenever a body _changes_ its state, it either combines with caloric, or separates from caloric.” “The most probable opinion concerning the nature of caloric,” says Mr. Dalton, “is that of its being an elastic fluid of great subtlety, whose particles repel one another, but are attracted by all other bodies. Every kind of matter has its peculiar affinity to heat, by which it requires a certain portion of the fluid, in order to be in equilibrium with other bodies at a certain temperature.”[55] It is now generally supposed, adds Mr. Parkes, that the air owes its elasticity to the caloric which it contains; and, that if it could be deprived entirely of this, it would lose its elastic form. The expansibility of the air is effected by the operation of caloric: for being rarefied by heat, it occupies a larger space than otherwise it would. It is extremely probable, says Lavoisier, that air is a fluid naturally existing in a state of vapor; or, as we may better express it, that our atmosphere is a compound of all the fluids which are susceptible of the vaporous or permanently elastic state, in the usual temperature, and under the common pressure.[56]