IN the brief time available to-night I shall not attempt elaborate arguments respecting my recent investigations, many of which are of mathematical character and of considerable length, and are given in my new work, “Researches on the Evolution of the Stellar Systems,” Vol. II., 1910; but shall content myself with a popular summary suitable for a general audience. In the first place, it should be remarked that although the New Cosmogony is the newest of the sciences, the Old Cosmogony dates back to the time of the Greek philosopher Parmenides, who was the revered teacher of Plato. On the whole, the progress of cosmogony throughout the centuries has been slow, very slow indeed; yet it has never entirely ceased, except during the Middle Ages. Eudoxus and other writers among the Greeks be- lieved that the heavenly bodies revolve in crystalline spheres, and had been set revolving in circles because the circle is a perfect geometrical figure, and was therefore preferred by the Deity for the orbits of the stars. After Kepler's discovery of 1609, that the planetary orbits are elliptical, it was necessary to modify these views to correspond to the true laws of nature. Both Kepler and Newton wondered at the roundness of the planetary orbits, but were unable to< assign the cause of this remarkable law of our system. No physical cause for the circularity of the planetary orbits was assigned prior to 1796, but in that year Laplace explained this property of the planetary paths by supposing that the planets had been detached in the form of rings which afterward condensed into globular masses. A similar explanation of the circularity of the satellite orbits was also put forth at the same time, so that all these bodies were supposed to have been detached by a gently accelerated rotation. The doctrine that the planets and satellites were thrown off by rotation has been current for more than a century, but it is now definitely proved to be erroneous, and has been quite abandoned by astronomers since the publication of my researches of the year 1908, showing that the roundness of the orbits is to * Address to the Popular Educational Society of San l (, rancico, August aoth, 1910. be explained by the secular effects of a resisting medium, and by no other cause whatsoever. Laplace's theory is therefore finally overthrown, and what is known as the capture theory substituted in its place. It is shown by accurate calculations based on Babi-net's criterion that the planets never were any part of the sun, but were formed in the outer parts of the solar nebula, and have since neared the sun, and had their orbits rounded up and made smaller and smaller. The satellites, including the terrestrial moon, have likewise been captured and added on to the planets which now govern their motions. The result of the capture theory is essentially a new nebular hypothesis, which explains all the known phenomena of our system, even the retrograde motion of the outer satellites of Jupiter and Saturn. In the old nebular hypothesis it was supposed that a nebula is a fluid mass in equilibrium under conditions of hydrostatic pressure, so that the rotation of the central nucleus transmitted pressure outward and aided 'in throwing off a ring of nebulous matter from the periphery; in the new nebular hypothesis there is no fluid pressure from the center outward—the bodies develop as independent nuclei in the nebula, and drift toward the larger centers of attraction. Thus the planets are added on to the sun from without, and the satellites added to their several planets. When the planets began to develop in our primordial nebula they were at great distances from the sun, and hence nearly as far away as the comets are now. Accordingly it is evident that our planets and comets were originally related. The comets which come to us from a great distance are the survivals from the outer shell of the primordial nebula—the matter of the inner part of the nebula having been eaten out to produce the sun and planetary system. This accords with the appearances of the other nebulae, which are shown to be excessively rare and of vast extent. It has taken us three centuries to find out the real meaning of the comets; but the light now thrown on the connection between planets and comets is worth all the labor which has been bestowed upon this difficult subject. The repulsion of the matter in the tails of comets from the sun is easily explained; for it is now shown that the nebula? themselves are formed from fine dust expelled from the stars by the action of repulsive forces; and as the comets are survivals of our primordial nebula, the repulsion of the volatile elements in the tails of comets is not remarkable. This dust drifts about hither and thither, and finally collects into clouds called nebulas. It is shown by astronomical photography that the whole background of the sky is more or less covered by a faint haze of nebulosity. When this nebulosity collects into dense clouds we have nebulas, and they begin to settle down and develop into cosmical systems. Accordingly it is now shown that the stars produce the dust which collects into nebulas, and finally develops into stars. So that the stars form the nebulas, and the nebulas in turn form the stars; and the universe is governed by a cyclical process, apparently of endless duration. The result of this whole investigation is a greatly improved theory of the starry heavens. One of the points of greatest interest attaches to the discovery that the congregation of the nebulas away from the Milky Way, with maximum accumulation near the poles of the Galaxy, is the result of the action of repulsive forces, under which fine cosmical dust expelled from the stars is driven as far away from the Milky Way as possible. Heretofore astronomers have had no general theory of the origin and distribution of the nebulas. As long ago as 1785 Sir William Herschel noticed a tendency in these cloud-like masses to gather in the regions of the heavens away from the Milky Way, and this law was further confirmed by Sir John Herschel about 1845; but no explanation of the facts thus established has been forthcoming. It is well known that I have been occupied with the study of Repulsive Forces about ten years, and have at length shown that the nebulas are formed from dust expelled from the stars, which in turn are formed from the condensation of nebulas. The tendency of the nebulas to avoid the Milky Way is due to the expulsion of the nebula-forming dust from the stratum of stars constituting the Milky Way, and therefore the clouds produced by the condensation or' this dust naturally accumulate in the regions remote from the Galaxy. As the nebulas develop into stars surrounded by systems of planets, it seems probable that they are gradually drawn back into the starry stratum, by the attraction of the stars lying in the plane of the Milky Way. One of the greatest and most fundamental facts established by the telescopic explorations of the Herschels on the arrangement of the sidereal universe thus finds a natural and simple explanation in accordance with known laws. It is thus clear that a complete theory of cosmical eyolution involves the action of both attractive and repulsive forces, and should enable us to explain all classes of the heavenly bodies, namely, suns and stars, double stars, single stars surrounded by planetary systems, habitable planets revolving about the fixed stars in nearly circular orbits, and rotating on their axes like the planets of the solar system; comets, variable stars, new or temporary stars, and finally the development of multiple stars and clusters. Accordingly Laplace's original nebular hypothesis, implying the formation of bodies by the throwing off of rings, is incorrect and now quite abandoned by astronomers. The most important physical cause at work to modify the motions of the heavenly bodies is the action of a resisting medium. The variable stars, especially the cluster variables, are due to planets revolving in such a medium and blazing up at the time of perihelion passage, and thus the periods are very regular. New stars are due to collision with large planets; hence the outbursts are of short duration. The discoveries made during the last two years have enabled me to reduce cosmogony to a new basis, by which it now becomes an exact science. The development of a new science is always of profound interest. In this connection I will merely point out how remarkably every part of the new Nebular Hypothesis, or Capture Theory, supports every other part; so that the whole work is knit together into a harmonious whole of such irresistible strength that it cannot be overthrown. The craters on the moon show the size of the small bodies originally composing our nebula; for these craters are proved to be indentations due to the impact of satellites against the moon's face, and not volcanic action, as was long believed. The new theory explains the rotations of the planets on their axes, and their obliquities, as well as the motions of the satellites and the roundness of their orbits. The comets, as already remarked, are the surviving fragments from the outer shell of the ancient nebula which formed our system, the matter of the inner parts having been eaten away in forming the sun and planets. Thus the planets and comets were originally related, and the relationship is further illustrated by the connection of the Asteroids with the short-period comets captured by Jupiter. It 'is shown by the researches of mathematicians that both of these classes of small bodies have been captured and thrown into their present positions by the disturbing action of this giant planet. A nebula might be not very inappropriately described as a cluster of comets so dense as to shine with a hazy light. One other result of deep interest is the increased extent of our solar system, • which is shown to be of vast dimensions. Neptune's orbit is so round that it cannot possibly be the outermost of our planets, and good reasons may be adduced for thinking that some of the unseen planets still revolving on the outer borders of our system may yet be discovered by observation, although the search will be difficult, owing to the great distance and faintness of the sun's light in these remote regions of space. I will add just one more concluding announcement, namely, that the planets now shown to revolve about the fixed stars are inhabited by some kind of intelligent beings, so that life is unquestionably a general phenomenon of the universe. It is well known that the late Prof. Newcomb expressed similar views in an address delivered at the dedication of the Flower Observatory, Philadelphia, in 1897. The proof is now much more complete than ever before; and men of science will have to admit life to be general on the countless worlds revolving about the fixed stars, or else concede that life upon the earth is an accident and a mistake, existing for hundreds of millions of years in direct violation of the laws of nature, which no philosopher could possibly admit; for this would be a reductio ad absurdum more convincing than those developed in the science of geometry and taught in the best schools and universities of the world. The life nourishing on the earth and believed to exist also on Mars and Venus is but a drop in the Pacific Ocean compared to that nourishing on the thousands of billions of habitable worlds now definitely proved to revolve about the fixed stars.