During the short historic period there was no record of such an event; still it would seem to be only through the collision of dark suns, of which the number must be increasing, that a temporary rejuvenescence of the heavens was possible, and by such ebbings and flowings of stellar life that the inevitable end to which evolution in its apparently uncompensated progress was carrying us could, even for a little, be delayed.  We could not refuse to admit as possible such an origin for nebulae.  In considering, however, the formation of the existing nebulae we must bear in mind that, in the part of the heavens within our ken, the stars still in the early and middle stages of evolution exceeded greatly in number those which appeared to be in an advanced condition of condensation.  Indeed, we found some stars which might be regarded as not far advanced beyond the nebular condition.  It might be that the cosmical bodies which were still nebulous owed their later development to some conditions of the part of space where they occurred, such as conceivably a greater original homogeneity, in consequence of which condensation began less early.  In other parts of space condensation might have been still further delayed, or even have not yet begun.  If light matter were suggested by the spectrum of these nebulae, it might be asked further, as a pure speculation, whether in them we were witnessing possibly a later condensation of the light matter which had been left behind, at least in a relatively greater proportion, after the first growth of worlds into which the heavier matter condensed, though not without some entanglement of the lighter substances.  The wide extent and great diffuseness of this bright-line nebulosity over a large part of the constellation of Orion might be regarded, perhaps, as pointing in this direction.  The diffuse nebulous matter streaming round the Pleiades might possibly be another instance, though the character of its spectrum had not yet been ascertained.

THE MOTIONS OF THE STARS.

Besides its more direct use in the chemical analysis of the heavenly bodies, the spectroscope had given to us a great and unexpected power of advance along the lines of the older astronomy.  In the future a higher value might, indeed, be placed upon this indirect use of the spectroscope than upon its chemical revelations.  By no direct astronomical methods could motions of approach or of recession of the stars be even detected, much less could they be measured.  A body coming directly toward us or going directly from us appeared to stand still.  In the case of the stars we could receive no assistance from change of size or of brightness.  The stars showed no true disks in our instruments, and the nearest of them was so far off that if it were approaching us at the rate of a hundred miles in a second of time, a whole century of such rapid approach would not do more than increase its brightness by the one-fortieth