The effect of heat in producing combination may be easily explained according to these ideas; it not only gives more freedom of motion to the particles, but in a number of cases it seems to exalt the electrical energies of bodies:--glass, the tourmaline, sulphur, and some others, afford familiar instances of this latter species of energy. In general, when the different energies are strong and in perfect equilibrium, the combination ought to be quick, the heat and light intense, and the new compound in a neutral state. This would seem to be the case in the combination of oxygen and hydrogen, which form water, a body apparently neutral in electrical energy to most others; and also in the circumstances of the union of the strong alkalies and acids. But where one energy is feeble, and the other strong, all the effects must be less vivid; and the compound, instead of being neutral, ought to exhibit the excess of the stronger energy. The grand principle thus developed may enable us to obtain new and useful indications of the composition of bodies, by ascertaining the character of their electrical energies; and we now find, in most modern works of Chemistry, that bodies are arranged according to their natural electrical relations; and are said to be ELECTRO-POSITIVE, or ELECTRO-NEGATIVE, according to their polarities. The advantage of such an arrangement must be freely acknowledged, for it has been the means of establishing analogies[63] of the utmost importance in chemistry, of which I shall adduce some striking examples in a subsequent part of the present work, when I shall endeavour to offer a general view of the revolution which chemical science has undergone during the investigations of Davy, and contemporary philosophers. [63] It will be sufficient for my present purpose to point out those existing between _Chlorine_, _Iodine_, and _Bromine_. After some further enquiries into the theory of the Voltaic pile,[64] to which an allusion has been already made, the author offers additional reasons for supposing the decomposition of the chemical menstrua essential to the continued electro-motion of the pile; and if the fluid medium could be a substance incapable of decomposition, there is every reason to believe the equilibrium would be restored, and the motion of the Electricity cease. Having shown the effects of _induction_, in increasing the electricity of the opposite plates, he arrives at the important conclusion, that in a Voltaic arrangement the _intensity of the Electricity increases with the number, but the quantity with the size of the plates_. A theory which was subsequently confirmed by the experiments of Mr. Children. [64] See page 226.