as any further liberation of gases from internal condensation must be due to solar contraction, hence gradual, and not sudden. Moreover, such liberation of hydrogen gas from within would show its spectrum loaded, at its earliest eruption, with absorption bands; and, finally, the convulsion presupposes as great an activity, and consequently as great a difficulty, before the phenomenon as the phenomenon itself presents; for such vast disturbance of mass would be more difficult to account for, and require more energy to produce, than the results themselves. Moreover, the whole mass of the star appeared to increase equally in temperature, as shown by the spectrum, and, if produced by an internal convulsion, this must have extended to, if not proceeded from, its core; so that while the combustion of hydrogen might have ceased in a very brief time, the intense heat of the solar mass could not have been dissipated for thousands of years. It would, in fact, have disrupted the whole orb. Another theory is that this vast incandescence was caused by the "violent precipitation of some mighty mass--perhaps a planet--upon the globe of that remote sun, by which the momentum of the falling mass would be changed into molecular motion; in other words, into heat and light." This theory is no more plausible than the other, since it fails to account for the enormous volume of hydrogen, with bright lines, as a result of such contact; while Professor Proctor very clearly shows that such contact would have been preceded, necessarily, by repeated partial grazings, as the outside body repeatedly passed in swifter and closer passage by the sun in its gradually approaching orbital revolutions, and that the increase of light and heat must have been measured by years instead of by hours. The same difficulties exist in the supposed passage of the star through nebulæ or star clouds, of which Professor Proctor says, "As for the rush of a star through a nebulous mass, that is a theory which would scarcely be entertained by any one acquainted with the enormous distances separating them.... All we certainly know suggests that the distances separating them from each other are comparable with those which separate star from star." In fact, no tenable theory has been advanced which will cover the phenomena. Professor Proctor describes a star which flamed out in 1876. At midnight, November 24, a star of the third magnitude was noticed in the constellation of the Swan; its light was very yellow; its brilliancy rapidly faded. On December 2 it was equal to a star of the fifth magnitude only, and the color, which had been yellow, was now greenish-blue. "The star's spectrum at this time consisted almost entirely of bright lines. December 5 he found three bright lines of hydrogen, the strong double line of sodium, the triple line of magnesium, and two other lines. One of these last seemed to agree exactly in position with a bright line belonging