subsequently developed during the processes which brought about its organization? According to the preceding view of the structure and constitution of a nebulous mass, the idea of the chaotic matter being maintained in a diffused and attenuated condition through the agency of heat, is by no means necessary. Indeed, the assumption that the primitive matter of the universe existed in a diffused gaseous condition, through the agency of excessive heat, is itself, prima facie, improbable. If it were absolutely universal, what became of the heat, and how did the cooling and condensation commence? Even if we suppose that the chaotic matter existed in enormous detached masses, what an inconceivable amount of heat must have been created, merely to be dissipated throughout the infinitudes of space! Such a view ill accords with our conceptions of the economy of the Creator's operations.
According to the views previously announced, the original concentration of the nebulous matter about a central nucleus was not the result of cooling and contraction, but of a gradual process of aggregation of discrete bodies under the action of mutually-attractive forces. Now, in the collisions and frictions necessarily incident to this process of aggregation, we have an indefinite supply of heat. The establishment of the "Dynamical Theory of Heat," on the sure basis of experiment and observation, assures us that when motion is checked or arrested, it is transformed into heat. Hence, we see that the collisions and destruction of velocity, incident to the process of aggregation, while imparting a motion of rotation to the nebulous mass, at the same time evolved heat, more or less, throughout its structure—and especially toward the nucleus, where the bodies, whose velocities had been checked, were gradually subsiding. The larger portion of the "dynamical energy" of the crowd of bodies aggregating toward the nucleus, was thus transformed into heat—a smaller portion remaining in the motion of rotation of the solar nebula. This view makes the heat and light-producing process continuous and gradual, and the true gaseous and fused conditions of the nebula, subsequent states, induced by the evolution of intense heat.
We thus reach a lofty point of view. Given diffused or chaotic matter, and mutual attraction, and the whole machinery of the Nebular Hypothesis is set in action! The "star-dust," or "world-stuff" begins to aggregate—heat is evolved—rotation is imparted—and all the apparatus required for the formation of suns, planets, and satellites, is established! Assuming that the processes of aggregation and heat-evolution had so far progressed that the rotating spheroid consisted of a more or less continuous mass of liquid or gas, extending far beyond the orbit of Neptune, and we are furnished with all the conditions assumed by Laplace.
It is unnecessary to follow the lecturer in his exposition of Laplace's reasoning, by which it was shown, upon mechanical principles, that, as the rotating spheroid slowly contracted and condensed by the grav-
