_Professor A. Winchell on the pre-nebular condition of matter._—This cosmical dust, or world-stuff, he considers to be scattered promiscuously through boundless space. It is cold and non-luminous, and is acted upon by forces of attraction and probably of repulsion. The material particles, either as atoms or less probably as molecules, are drawn by mutual attraction into groups and swarms. Any central attractive force, as of a sun or planet, by causing the particles to move in converging lines, would cause them to become approximated and ultimately aggregated. Thus both mutual attractions and centric movements would tend to produce aggregations dispersed through space. But in the presence of two or more attractive centres, as in the present constitution of the Cosmos, it is impossible that any mass shall fall directly upon its centre of attraction. Hence motions of rotation will be established in the mass, and also orbital motions of masses about each other. In addition to the mutual attraction of the molecules, the convergence of their paths towards centres of attraction must also tend to the formation of masses and swarms of masses and particles. “We have then,” he says, “to picture indefinite space as pervaded by swarms of masses and particles of dark matter. Each mass or particle may, nevertheless, be separated by thousands of miles. It is manifest, therefore, that each mass or particle will eventually dispose itself, under the fixed action of the forces of matter, in some definite order. It is manifest also, from what has been said, that each swarm will have a progressive motion along a path having the essential character of an orbit around some dominant centre of attraction. If, as seems to be the fact, an ethereal medium, or any condition of interplanetary matter, exists in space, it opposes the movements of these swarms by opposing the motion of each constituent mass. But the smaller masses—the particles and molecules—would feel this resistance to the greatest extent. They would therefore fall behind the heavier masses, and would be most deflected toward the attracting centre. The smallest particles would be driven farthest to the rear, and dispersed farthest from the orbit of the train, along the side turned toward the principal attraction. The swarm would present an elongated form, in which the larger and heavier masses would move foremost, and nearest the line of the orbit—that is, near the exterior skirt of the area covered by the general swarm—while the smaller ones would follow, in graduated succession, in a long train which would present a fan-like expansion lying mostly on the inside of the path of the principal masses.”