the formula of Fourier, before it has reached the required hundred, will have found a nucleus in complete fusion, acting intensely upon the thin external crust, and seeking through every crevice of these “flagrantia mœnia mundi,” to issue forth in torrents of fire. It has been farther objected to a central fluidity, that such a fluid must be in constant circulation by the cooling of its exterior—a fact ascertained in the case of all fused metals. Tides too, it has been argued, would be produced in the fluid matter, however deeply seated, through the influence of the sun and moon, and which _tides_ would necessarily occasion such oscillatory and expansive movements as astronomy has neither noticed nor accounted for. Again, the supposition of a central heat of the earth, prevailing from the beginning and through all the phases of its history, implies that its cooling is still going on; and that, in consequence, a contraction in the mass or bulk of the earth will follow the law observed by all other bodies in parting with their heat. Hence this contraction might lead to the shortening of the day and other mechanical results. But Laplace satisfied himself, by reference to ancient astronomical records, that there had been no alteration in the length of the day, even to the smallest calculable degree or point of a second; and that thence, the hypothesis of a fluid, or even primitive heat of the earth, had here no confirmation. An objection to the theory has likewise been urged, from the well-known property and tendency of heat to become equally diffused through all the particles of any body in which it exists. Thus, it is an established principle, that heat not only diffuses itself on all sides, but passes continually from bodies in which the temperature is greater to those in which it is less; and that if a body be placed in a medium having a temperature different from its own, the momentary variations of its temperature will be as the differences between the temperature of the body and of the medium. Hence, when the heat beneath the surface of the earth, at whatever depth, becomes of sufficient intensity to melt iron, it cannot pass beyond this until the whole surrounding mass is heated to the same degree of intensity. The law of increment and transmission of caloric, it is argued, must be the same below as above; and, assuming the nucleus of the earth to be fluid, no solid crust could thus be formed upon the surface until every particle of the heated fluid mass was cooled down to the point of consolidation. This principle is well understood in the formation of a crust of ice upon water. If extendible to other bodies, and to subterranean distances, then the simple fact of an existing outer crust, solid and cooled down to the existing temperature, militates against the probability of a central fire, and is utterly repugnant to the hypothesis of a liquid central mass.