To this it may be replied that the primitive igneous fluidity of the earth and planets was a necessary consequence of their condensation—a fact which has no inconsistency with the theory in question.
A different mechanical theory of the origin of solar heat is advocated by Professor Helmholtz in his interesting work On the Interaction of Natural Forces. In regard to the sun he says: "If we adopt the very probable view, that the remarkably small density of so large a body is caused by its high temperature, and may become greater in time, it may be calculated that if the diameter of the sun were diminished only the ten-thousandth part of its present length, by this act a sufficient quantity of heat would be generated to cover the total emission for 2100 years. Such a small change besides it would be difficult to detect by the finest astronomical observations."[25] The same view is adopted by Dr. Joel E. Hendricks, of Des Moines, Iowa.[26]
[CHAPTER X.]
WILL THE METEORIC THEORY ACCOUNT FOR THE PHENOMENA OF VARIABLE AND TEMPORARY STARS?
Having shown that meteor-asteroids are diffused in vast quantities throughout the universe; that according to eminent physicists the solar heat is produced by the precipitation of such matter on the sun's surface; and that Leverrier has found it necessary to introduce the disturbing effect of meteoric rings in order fully to account for the motion of Mercury's perihelion; we now propose extending the meteoric theory to a number of phenomena that have hitherto received no satisfactory explanation.
Variable and Temporary Stars.
No theory as to the origin of the sun's light and heat would seem to be admissible unless applicable also to the sidereal systems. Will the meteoric theory explain the phenomena of variable and temporary stars?
"It has been remarked respecting variable stars, that in passing through their successive phases, they are subject to sensible irregularities, which have not hitherto been reduced to fixed laws. In general they do not always attain the same maximum brightness, their fluctuations being in some cases very considerable. Thus, according to Argelander, the variable star in Corona Borealis, which Pigott discovered in 1795, exhibits on some occasions such feeble changes of brightness, that it is almost impossible to distinguish the maxima from the minima by the naked eye; but after it has completed several of its cycles in this manner, its fluctuations all at once become so considerable, that in some instances it totally disappears. It has been found, moreover, that the light of variable stars does not increase and diminish symmetrically on each side of the maximum, nor are the successive intervals between the maxima exactly equal to each other."—Grant's History of Physical Astronomy, p. 541.
Of the numerous hypotheses hitherto proposed to account for these phenomena we believe none can be found to include and harmonize all the facts of observation. The theories of Herschel and Maupertius fail to explain the irregularity in some of the periods; while those of Newton and Dunn afford no explanation of the periodicity itself.[27] But let us suppose that among the fixed stars some have atmospheres of great extent, as was probably the case with the sun at a remote epoch in its history. Let us also suppose the existence of nebulous rings, like those of our own system, moving in orbits so elliptical that in their perihelia they pass through the atmospheric envelopes of the central stars. Such meteoric rings of varying density, like those revolving about the sun, would evidently produce the phenomena of variable stars. The resisting medium through which they pass in perihelion must gradually contract their orbits, or, in other words, diminish the intervals between consecutive maxima. Such a shortening of the period is now well established in the case of Algol. Again, if a ring be influenced by perturbation the period will be variable, like that of Mira Ceti. A change, moreover, in the perihelion distance will account for the occasional increase or diminution of the apparent magnitude at the different maxima of the same star. But how are we to account for the variations of brightness observed in a number of stars where no order or periodicity in the variation has as yet been discovered? It is easy to perceive that either a single nebulous ring with more than one hiatus, or several rings about the same star, may produce phenomena of the character described. Finally, if the matter of an elliptic ring should accumulate in a single mass, so as to occupy a comparatively small arc, its passage through perihelion might produce the phenomenon of a so-called temporary star.