Robert Stawell Ball

“ The condensation of a nebula could be followed in the same manner as we can study the growth of the trees in the forest, by comparing the trees of various ages which the forest contains at the same time. In attempting to pronounce on the evidence with regard to Herschel’s theory, we must at once admit that the transmutation of a nebula into a star has never been seen. ”

“ In fact a little consideration of the theory of probabilities will show it to be infinitely probable that such an object should really have some movement of rotation, no matter by what causes the nebula may have originated. As this vast mass cooled it must by the laws of heat have contracted towards the centre, and as it contracted it must, according to a law of dynamics, rotate more rapidly. The time would then come when the centrifugal force on the outer parts of the mass would more than counterbalance the attraction of the centre, and thus we would have the outer parts left as a ring. ”

“ It is indeed very doubtful whether any changes of a nebula have ever been seen which are of the same character as the changes Herschel’s theory would require. It seems, however, most likely that the periods of time required for such changes are immense and that the changes accomplished in only a century or two are absolutely inappreciable. ”

“ We do not know whether the comets are really indigenous to the solar system or whether they may not be merely imported into the system from the depths of space. Even if the comets be indigenous to the system, they may, as many suppose, be merely ejections from the sun. In any case the orbits of comets are exposed to such tremendous perturbations from the planets that it is unsafe from the present orbit of a comet to conjecture what that orbit may have been in remote antiquity. On these grounds we discuss the nebular theory without much reference to comets. ”

“ The nebular theory offers an explanation of this most remarkable uniformity. Laplace supposed the existence of a primeval nebula which extended so far out as to fill all the space at present occupied by the planets. This gigantic nebulous mass, of which the sun was only the central and somewhat more condensed portion, is supposed to have a movement of rotation on its axis. There is no difficulty in conceiving how a nebula, quite independently of any internal motion of its parts, shall also have had as a whole a movement of rotation. ”

“ Should any one be sceptical as to the sufficiency of these laws to account for the present state of things, science can furnish no evidence strong enough to overthrow his doubts until the sun shall be found growing smaller by actual measurement, or the nebulae be actually seen to condense into stars and systems. ”

“ It is also remarkable that all the great planets and many of the small ones have their orbits very nearly in the same plane, and nearly circular in form. Viewed as a question in probabilities, we calculate the chance that five hundred bodies revolving round the sun shall all be moving in the same direction. ”

“ There are other nebulae in which a nucleus can be just discerned, others again in which the nucleus is easily seen, and still others where the nucleus is a brilliant star-like point. The transition from an object of this kind to a nebulous star is very natural, while the nebulous stars pass into the ordinary stars by a few graduated stages. It is thus possible to exhibit a series of objects beginning at one end with the most diffused nebulosity and ending at the other with an ordinary fixed star or group of stars. ”