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SCIENCE 



[N. S. Vol. XXX. No. 775 



II. Constructive (in the main) 

 The preceding work was chiefly destructive, 

 "but there were three notable exceptions: (1) 

 The opening of the way to construction on 

 planetoidal lines; (2) the determination of 

 rather rigorous criteria that must be met in 

 forming a tenable hypothesis, viz., the condi- 

 tions must he such as to give low mass, high 

 moment of momentum and irregular distribu- 

 tion of matter to the outer part of the system, 

 and high m,ass, low moment of momentum 

 and sphericity to the central part; and (3) 

 the recognition that spiral nebulae offered the 

 greatest probability of meeting these criteria 

 and of having at the same time a planetoidal 

 organization.^ A summation of the leading 

 points made in the destructive work, together 

 with a statement of the constructive criteria 

 above named and of the grounds for giving 

 precedence to spiral nebulae in the search for 

 an origin of the solar system, was published 

 in Science, August 10, 1900, by Ohamberlin 

 and Moulton jointly. 



Fifth Step. — Considerable futile work was 

 done, largely by Ohamberlin, in trying out 

 the possibilities of collision between nebulous 

 bodies as a mode of origin of spiral nebulae, 

 but no escape was found from the high proba- 

 bility, amoxinting almost to certainty, that the 

 resulting orbits would be too eccentric to fit 

 the case of the solar system in any instance 

 that was likely to occur. 



Sixth Step. — The effects of the differential 

 attractions exerted by bodies on one another 

 when they make close approaches were then 

 studied by Chamberlin in the lines marked 

 out by Roche, Maxwell and others, and found 

 to be a promising field for hypothesis respect- 

 ing the origin of meteorites, comets and neb- 

 ulae. This study included not merely the 

 direct tidal effect on a passive body, following 

 Eoehe, but also the projective effect developed 

 in a body of enormous elasticity already under 

 high pressure and affected by violent local 

 explosions which were subject to intensifica- 



' Chamberlin in Journal of Oeology, VIII., 

 January-February, 1900, pp. 72-73; Moulton, 

 Astrophysical Journal, XI., March, 1900, p. 130. 



tion by the changes of gravity brought to bear 

 on them by a passing body. It was shown 

 that the contingency of close approach was 

 much greater than that of collision, and that 

 the results, (1) in the case of the disrupting 

 of solid bodies, afforded a felicitous basis for ex- 

 plaining the erratic orbits of comets, the clus- 

 tered fragments of the comet heads, and the 

 angularity of the meteorites into which they 

 are supposed to be finally dispersed; while (2) 

 the explosive projections from suns under the 

 influence of the passing body gave a reason 

 for the two-armed feature of most spiral neb- 

 ulae — a neglected feature to which attention 

 was specially called — for the spiral form, for 

 the knots and haze, and at the same time 

 offered a basis for inferring their dynamical 

 state. These radical hypotheses were set forth 

 in a paper entitled " On a Possible Function 

 of Disruptive Approach in the Formation of 

 Meteorites, Comets and Nebulae," by T. 0. 

 Chamberlin, Astrophys. Jour., Vol. XTV., 

 July, 1901, pp. 17-40; also Jour. Geol, Vol. 

 IV., 1901, pp. 369-393. 



Seventh Step. — With these conceptions of 

 the origins and dynamical states of meteorites 

 and spiral nebulse as the bases of alternative 

 hypotheses, a more critical study was made of 

 the probabilities of origin of the solar system 

 from swarms of meteorites of heterogeneous 

 and quasi-gaseous organization, and, more 

 radically, of the probabilities of the origin of 

 such swarms either by concentration from a 

 state of greater diffusion or by the dispersion 

 of some previous body. Conditions favorable 

 to the evolution of the solar system were not 

 found, except when the meteoric organization 

 took the planetesimal form.* Specifically, the 

 conclusion reached was that the heterogeneous 

 meteoritic state is " inherently moribund, pass- 

 ing into the gaseous state on the one hand, or 

 into the planetesimal on the other, or, in the 

 absence of assemblage, losing its constituents 

 to existing suns and planets by capture one 

 by one." ° 



* Chamberlin in Year Book No. 3, Carnegie 

 Institution of Washington, 1904, pp. 195-208. 

 'Ibid., p. 208. 



