Dr. Faraday has proved, by experiments on bodies both in solution and fusion, that chemical affinity is merely a result of the electrical state of the particles of matter. Now it must be observed that the composition of bodies, as well as their decomposition, may be accomplished by means of electricity; and Dr. Faraday has found that this chemical composition and decomposition, by a given current of electricity, is always accomplished according to the laws of definite proportions; and that the quantity of electricity requisite for the decomposition of a substance is exactly the quantity necessary for its composition. Thus the quantity of electricity which can decompose a grain weight of water is exactly equal to the quantity of electricity which unites the elements of that grain of water together, and is equivalent to the quantity of atmospheric electricity which is active in a very powerful flash of lightning. This law is universal, and of that high and general order which characterises all great discoveries. Chemical force is extremely powerful. A pound of the best coal gives when burnt sufficient heat to raise the temperature of 8086 pounds of water one Centigrade degree, whence Professor Helmholtz of Bonn has computed that the magnitude of the chemical force of attraction between the particles of a pound of coal and the quantity of oxygen that corresponds to it, is capable of lifting a weight of 100 pounds to the height of 20 miles. Dr. Faraday has given a singular instance of cohesive force inducing chemical combination, by the following experiment, which seems to be nearly allied to the discovery made by M. Dœbereiner, in 1823, of the spontaneous combustion of spongy platinum (N. 171) exposed to a stream of hydrogen gas mixed with common air. A plate of platinum with extremely clean surfaces, when plunged into oxygen and hydrogen gas mixed in the proportions which are found in the constitution of water, causes the gases to combine and water to be formed, the platinum to become red-hot, and at last an explosion to take place; the only conditions necessary for this curious experiment being excessive purity in the gases and in the surface of the plate. A sufficiently pure metallic surface can only be obtained by immersing the platinum in very strong hot sulphuric acid and then washing it in distilled water, or by making it the positive pole of a galvanic pile in dilute sulphuric acid. It appears that the force of cohesion, as well as the force of affinity, exerted by particles of matter, extends to all the particles within a very minute distance. Hence the platinum, while drawing the particles of the two gases towards its surface by its great cohesive attraction, brings them so near to one another that they come within the sphere of their mutual affinity, and a chemical combination takes place. Dr. Faraday attributes the effect in part also to a diminution in the elasticity of the gaseous particles on their sides adjacent to the