And the same laws that governed the formation of the earth, governed also the formation of the moon: the variations of Nature’s operations are _quantitative_ only and not _qualitative_. The Divine Will that made the earth made the moon also, and the means and mode of working were the same for both. The geological phenomena of the earth afford unmistakeable evidence of its original fluid or molten condition, and the appearance of the moon is as unmistakeably that of a body once in an igneous or molten state. The enigma of the earth’s primary formation is solved by the application of the dynamical theory of heat. By this theory the generation of cosmical heat is removed from the quicksands of conjecture and established upon the firm ground of direct calculation: for the absolute amount of heat generated by the collision of a given amount of matter is (of course, with some little uncertainty) deducible from a mathematical formula. Mayer has computed the amount of heat that the matter of the earth would have generated, if it had been formed originally of only two parts drawn into collision by their mutual attraction, and has found that it would be from 0 to 32,000 or 47,000[1] Centigrade degrees, according as one part was infinitely small as compared with the other, or as the two parts were of equal size. Professor Helmholtz, another labourer in the same field of science, has computed the amount of heat generated by the condensation of the whole of the matter composing the solar system: this he finds would be equivalent to the heat that would be required to raise the temperature of a mass of water equal to the sum of the masses of all the bodies of the system to 28,000,000 (twenty-eight million) degrees of the Centigrade scale. These examples afford abundant evidence of sufficient heat having been generated by the aggregation of the matter of the moon to reduce it to a state of fusion, and so to produce, from a nebulous chaos of diffused cosmical matter, a molten body of definite outline and size.