Page Two 



EVOLUTION 



March. 1929 



New Worlds in the Making 



By CLYDE FISHER 



E\' J'^ Jv V O N E, after some observation of the 

 heavenly bodies, begins to wonder at their origin. 

 There is abundant evidence that the earth has not al- 

 ways been just as it is now. Even a superficial study 

 of geology convinces one that the earth has a life 

 story, if we can but read the record. And the more 

 we examine the worlds outside of ours, the more we 

 are persuaded that changes have been going on 

 throughout the universe. 



The first scientific theory of the origin of our solar 

 system goes back to the philosophers Kant and Swe- 

 denborg. It was then developed and put into scientific 

 form by La Place and became known as the Nebular 

 Theory. According to this theory, the sun, all the 

 planets and their satellites and the asteroids were once 

 a huge, rotating, gaseous nebula, which extended out 

 beyond the present orbit of Neptune. As this nebulous 

 mass cooled, it contracted and its speed of rotation 

 increased. This increase in the speed of rotation was 

 accompanied by an increase in the centrifugal force 

 by which a revolving body tends to fly from the 

 center. 



So it was with the outer part of this theoretical 

 nebula. When this force had increased until it balanced 

 the gravitational pull toward the center, the inner part 

 of the nebulous mass contracted away from the outer 

 rim. This rim was not thrown ofif like mud from a 

 carriage-wheel, but was left balanced between gravity 

 and its centrifugal force of rotation. This rim, which 

 may not have been complete or even uniformly thick, 

 was supposed to be collected together in a globular 

 mass by the gravitational attraction of each particle 

 for every other. Thus the outermost planet was first 

 formed. In the same way the rest of the planets were 

 successively formed, the one nearest the sun being the 

 last formed. In the case of the asteroids, the tiny 

 planets between the orbits of Jupiter and Mars, it was 

 supposed that this rim gathered into more than a 

 thousand small masses. 



The moons or satellites of the planets were sup- 

 posed to have been formed in the same way, after 

 each planet mass had been left balanced between 

 gravity and centrifugal force, and still revolving 

 around the central portion of the original nebulous 

 mass. 



As the nebulous matter condensed and cooled, it 

 changed from gas to liquid and then to solid, at least 

 in the case of the four inner planets. Mercury, Venus, 

 Earth and Mars. The four outer and larger planets, 

 Jupiter, Saturn, Uranus and Neptune, still seem to 

 present only an outer surface of cloud. 



When the nebular theory was first conceived, it was 

 thought to have two kinds of evidence in its favor, 

 first, features in our solar system which the theory 

 would account for, and second, systems outside our 

 own now in phases suggesting the early stages of our 

 own. 



Evidence of the first kind was most impressive, for 



it was thought the tlieory would explain the following 

 conditions : 1 ) The planetary and most asteroid orbits 

 are nearly in the same plane ; so as to occupy a narrow 

 belt in the heavens; 2) These orbits are nearly circular; 

 3) All the planets and asteroids revolve around the 

 sun in the same direction; 4) The sun also rotates in 

 that direction and its equator is but little inclined to 

 their orbits; 5) The satellites revolve about the planets 

 in the same direction in orbits nearly circular and near- 

 ly in the plane of each planet's equator (except two 



Planet Solum and Its Rings once thought to illustrate stage 

 in evolution of Solar System 



satellites of Jupiter and one of Saturn) ; and 6) The 

 planets of the greater density are nearer the sun. If 

 these relations were due to chance, we would have 

 ex|>ected to find the planets and asteroids scattered 

 over the sky and revolving around the sun or each 

 other in many diverse ways. The conditions as they 

 are point to a common origin and an orderly develop- 

 ment. 



The second kind of evidence, the phases in systems 

 outside which suggest stages in the development of 

 our own solar system, consisted largely of nebulae. 

 No telescope is powerful enough to reveal planetary 

 systems around any of the stars, even if they exist. 

 The Great Nebula in Andromeda and that in the sword 

 of Orion can lie seen with the naked eye, and many 

 more were discovered with the telescope. Sir William 

 Herschel observed faint diffused nebulae, others in 

 which a nucleus can just be discerned, and others in 

 which the nucleus is a brilliant star-like point. And 

 the spiral nebulae certainly appeared to be solar 

 systems in the process of development. Larger teles- 

 cope resolved some of the so-called nebulae into stars. 

 At first this was thought to be fatal to the nebular 

 theory, because of the natural conclusion that still 

 larger telescopes might resolve the rest of the nebulae 

 into stars. But the invention of the spectroscope proved 

 that some nebulae were really gaseous and so re- f{ 

 established the nebular theory. 



But in recent years, the nebular theory has lost 

 ground. The spiral nebulae are now believed to be 

 immense universes outside of our own galactic 

 system. (See front cover.) 



