JfLT 23, 1909] 



SCIENCE 



115 



haze as matter to be added to the nuclei to form 

 the planets. It assumes that both the knots and 

 particles of the nebulous haze moved about the 

 central mass in elliptical orbits of considerable, 

 but not excessive, eccentricity. It postulates a 

 simple mode of origin of the nebula connected 

 with the not improbable event of a close approach 

 of the ancestral sun to another large body, but 

 the main hypothesis is not dependent on this 

 postulate. 



It assigns the gathering-in of the planetesimals 

 to the crossing of the elliptical orbits in the 

 course of their inevitable shiftings. Out of this 

 process and its antecedents, it develops consistent 

 views of the requisite distribution of mass and 

 momentum, of the spacing-out of the planets, of 

 their directions of rotation, of their variations 

 of mass, of their varying densities, and of other 

 peculiarities. 



It deduces a relatively slow growth of the earth, 

 with a rising internal temperature developed in 

 the central parts and creeping outward. With 

 such a mode of growth, the stages of the earth's 

 early history necessarily depart widely from those 

 postulated by the Laplacian and the nieteoritic 

 hypotheses. These stages now claim our atten- 

 tion. 



In my " Introduction to Astronomy," pp. 

 463^87 (1906), I have discussed the same 

 theory under the title of The Spiral Nebula 

 Hypothesis. Some of the headings of the 

 articles in this section are : Hypotheses Re- 

 specting the Antecedents of our Present 

 System, A Possible Origin of Spiral Nebulas, 

 The Development of the Solar System from 

 a Spiral Nebula, The Origin of Planets, The 

 Origin of Satellites, The Planes of the 

 Planetary Orbits, Rotation and Equatorial 

 Acceleration of the Sun, The Small Eccen- 

 tricities of the Planetary Orbits, The Rota- 

 tions of the Planets, The Eccentricities of the 

 Satellite Orbits, The Moment of Momentum 

 of the System, The Evolution of the Planets, 

 The Age of the Solar System, The Future of 

 the System. . . . The chapter is closed with 

 the following summary : 



The first word should be one of warning that 

 the theory which has been sketched briefly should 

 not be accepted as final. There are many points 

 where quantitative results must be obtained and 

 compared with our actual system. There may be 

 many modifications of it possible and necessary. 



For example, the genesis of spiral nebulas may be 

 different from that postulated above. 



The hypothesis of an original spiral nebula is 

 suggested by recent photographs of nebulas as 

 well as by the system itself. The conditions which 

 are supposed to have given rise to the spiral 

 nebula seem most reasonable in view of the mo- 

 tions of the stars. The development of a spiral 

 nebula by the near approach of two suns seems 

 to be a necessary consequence, though this point 

 needs further elaboration. The development of 

 some such a system as ours from a small spiral 

 nebula of the type considered seems to be inevit- 

 able. So far as the details have been worked out 

 nothing directly contradictory to the theory, or 

 even seriously questioning it, has been found, 

 while it explains admirably all the main features 

 of the system. It can be safely said that, at 

 present, this hypothesis satisfies all the require- 

 ments of a successful theory much better than any 

 previous one. 



Since the publication of these books the 

 work of elaborating and testing the theory has 

 been carried forward by both Professor 

 Chamberlin and myself, and a part of the re- 

 sults obtained have been published by the 

 Carnegie Institution. 



The alleged twenty-five years of uninter- 

 rupted work upon the evolution of the solar 

 system by See have resulted only in the fol- 

 lowing papers so far as I am aware: (1) 

 " Significance of the Spiral Nebula," Popular 

 Astronomy , pp. 614—616 (December, 1906) ; 

 (2) " On the Cause of the Remarkable Cir- 

 cularity of the Orbits of the Planets and 

 Satellites and on the Origin of the Planetary 

 System," Astronomische NachricMen, No. 

 4.308 (February 24, 1909), the same paper 

 printed in Popular Astronomy, May, 1909, 

 and at least the substance of the same paper 

 communicated by its author to the Chicago 

 Record-Herald early in 1909. 



In the paper in Popular Astronomy , written 

 over the date October 23, 1906, See makes the 

 following statements: 



For a number of years the writer has given 

 consideration to the probable nature of the spiral 

 nebula;, and their importance has been consider- 

 ably increased by photographs obtained by Roberts 

 and Keeler, and more recently at the Yerkes 

 Observatory. Certain speculations have been in- 



