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SCIENCE. 



[N. S. Vol. XXII. No. 557. 



attention to the resemblance to a planetary 

 system. It may not, perhaps, be fanciful 

 to imagine that some general mathematical 

 method devised for solving a problem of 

 cosmical evolution may find another appli- 

 cation to miniature atomic systems, and 

 may thus lead onward to vast developments 

 of industrial mechanics. Science, however 

 diverse its aims, is a whole, and men of 

 science do well to impress on the captains 

 of industry that they should not look 

 askance on those branches of investigation 

 which may seem for the moment far be- 

 yond any possibility of practical utility. , 



The theory which I have now explained 

 points to the origin of the sun and planets 

 from gradual accretions of meteoric stones, 

 and it makes no claim to carry the story 

 back behind the time Avhen there was al- 

 ready a central condensation or sun about 

 which there circled another condensation or 

 planet. But more, than a century ago an 

 attempt had already been made to recon- 

 struct the history back to a yet remoter 

 past, and, as we shall see, this attempt was 

 based upon quite a different supposition as 

 to the constitution of the primitive solar 

 system. I myself believe that the theory 

 I have just explained, as well as that to 

 which I am coming, contains essential ele- 

 ments of truth, and that the apparent dis- 

 cordances will some day be reconciled. The 

 theory of which I speak is the celebrated 

 nebular hypothesis, first suggested by the 

 German philosopher Kant, and later re- 

 stated independently and in better form 

 by the French mathematician Laplace. 



Laplace traced the origin of the solar 

 system to a nebula or cloud of rarefied gas 

 congregated round a central condensation 

 which was ultimately to form the sun. 

 The whole was slowly rotating about an 

 axis through its center, and, under the 

 combined influences of rotation and of the 

 mutual attraction of the gas, it assumed a 

 globular form, slightly flattened at the 



poles. The primeval globular nebula is 

 undoubtedly a stable or persistent figure, 

 and thus Laplace's hypothesis conforms to 

 the general laws which I have attempted 

 to lay down. 



The nebula must have gradually cooled 

 by radiation into space, and as it did so the 

 gas must necessarily have lost some of its 

 spring or elasticity, thus permitting a 

 greater degree of condensation of the 

 whole. The contraction led inevitably to 

 two results: first, the central condensation 

 became hotter; and, secondly, the speed of 

 its rotation became faster. The accelerated 

 rotation led to an increase in the amount 

 of polar flattening, and the nebula at length 

 assumed the form of a lens, or of a disk 

 thicker in the middle than at the edges. 

 Assuming the existence of the primitive 

 nebula, the hypothesis . may be accepted 

 thus far as practically certain. 



From this point, however, doubt and 

 difficulty enter into the argument. It is 

 supposed that the nebula became so much 

 flattened that it could not subsist as a con- 

 tinuous aggregation of gas, and a ring of 

 matter detached itself from the equatorial 

 regions. The central portions of the 

 nebula, when relieved of the excrescence, 

 resumed the more rounded shape formerly 

 possessed by the whole. As the cooling 

 continued, the central portion in its turn 

 became excessively flattened through the 

 influence of its increased rotation; another 

 equatorial ring then detached itself, and 

 the whole process was repeated as before. 

 In this way the Avhole nebula was fissured 

 into a number of rings surrounding the 

 central condensation, whose temperature 

 must by then have reached incandescence. 



Each ring then aggregated itself round 

 some nucleus which happened to exist in its 

 circumference, and so formed a subordinate 

 nebula. Passing through a series of trans- 

 formations, like its parent, this nebula was 



