In these instances a large quantity of heat is rendered sensible, as if it had been squeezed out by the force with which the particles combined, from interstices, which were filled with, what we may be allowed to call, an atmosphere of heat. Hence we conclude that, amongst the influences determining the molecular constitution of a body, heat performs an important part. All these facts go to prove that the atoms which form the compound body, whatever may be its character, are disposed of as so many centres of force, which act by influences of a peculiar character upon each other. That these influences are dependent upon known physical forces is certain; but the laws by which the powers of the ultimate atom are altered remain still unknown. In the great operations of nature, changes are produced which we cannot understand, and variations of condition do certainly occur, which may be regarded as instances of transmutation. Amongst others, we may adduce the different states in which we know carbon to exist. We have the diamond with its beautiful light-refracting property, its hardness and high specific gravity, capable of being converted into graphite and coke.[29] Charcoal, graphite, and the diamond, are totally unlike each other, yet we know they are each composed of the same atoms. Charcoal is a black irregular substance, light, and readily inflammable; graphite is crystallizable; but the forms of its crystals cannot be referred to those of the diamond, and it burns with difficulty. The diamond occurs in the most regular and beautifully transparent forms; and it can be burned only at the highest artificial temperatures. We are, however, convinced by experiment that the brilliant and transparent gem is made up of the same atoms as those which go to form the dull black mass of charcoal. From diamonds, as is above stated, coke has been formed by the heat of the voltaic battery, and recent experiments have proved that the volatilized carbon constantly passing off from one of the poles of a sufficiently powerful battery, is deposited in a crystalline powder, possessing most of the properties, as it regards hardness, &c. of true diamond dust. What is the mystery of this? We know not. The peculiar conditions have been the subjects of anxious study; but science has not yet let in a ray of light upon the mystery. That a different state--it has been called an _allotropic_ condition--is often induced in the same class of atoms is certain; and hence the variety of the resulting compounds. To continue our illustrations with carbon--may not its combinations, in uniform proportions with oxygen and hydrogen,[30] owe their differences to some allotropic change in the ultimate atoms of this element.