The sun is the principal orb of our system, and by far the most conspicuous, and the most observed of all observers, astronomers included. But we have seen already how contradictory their measurements of his distance, and their observations of the influence of his spots. Far more conflicting are the theories as to his constitution, of which indeed we may truly say very little was known before the application of photography and the spectroscope to heliography within the last seven years. One astronomer fixed the period of his rotation at twenty-five days, fourteen hours, and eight minutes; another at twenty-six days, forty-six minutes; another at twenty-four days, twenty-eight minutes.[341]
In regard to the sun's heat, a matter fundamental to the nebular theory, the calculations differ widely, and some of them must be grossly erroneous. M. Vicaire called the attention of the French Academy, at a recent meeting, to this unsatisfactory condition of science. Father Secchi estimates it at eighteen million Fahrenheit; while Pouillet says it ranges from two thousand six hundred and sixty-two to three thousand two hundred and one; and others range from two hundred thousand downward. The most singular thing is that these results are derived from observations or radiations made by apparatus identical in principle.[342] But Waterston calculates the temperature of the solar surface at above ten, and probably twelve million Fahrenheit.[343]
Now what feeds these enormous fires? The old opinion of astronomy, that the sun was a mass of fire, was assailed by Sir Wm. Herschel, who maintained that it was in the condition of a perpetual magnetic storm. This notion was altered into the belief of a central dark body, surrounded by a stratum of clouds, outside of which is a photosphere of light and heat; which some made one thousand five hundred miles in depth, others four thousand. Outside of this was another layer of rose-colored clouds. To this theory Arago, Sir John Herschel and Humboldt assented. But Le Verrier declares that the facts observed during late eclipses are contrary to this theory, and a new theory is slow in process of construction, to be demolished in its turn by later observations.[344]
One of the most recent theories is that the fuel is furnished by a stream of meteorites, planetoids, and comets, falling in by the power of attraction, and being speedily converted into gas flames; a process the very reverse of the theory of the evolution of the solid celestial bodies from gas. But it is pretty evident from these conflicting theories that nobody knows anything certainly as to the materials of the sun, or the fuel which feeds his flames. But if the very best astronomers do not know of what he is made, is it not too great a demand upon our credulity to ask us to believe that they can tell how he was made?
The size, density, and distances of the planets, which form such essential elements in the calculations of the nebular theory of evolution, are equally uncertain. Ten or twelve years ago Mercury was believed to be nearly three times as dense as the earth (2.94); and the theory of evolution was partly based upon this assumed fact. But Hausen now finds that it is not half so dense; that, as compared with the earth, it is only 1.22; and that its mass is less than half (5/12) of what had been confidently calculated.[345] Corrections of the masses and densities of other planets are also offered.
Still wider differences prevail in calculating the velocities of these bodies; velocities calculated and found to correspond with the theory of evolution. Bianchini gives the period of the rotation of Venus at twenty-four days, eight hours; but Schroeter says it is not as many hours as Bianchini gives days; that it is only twenty-three hours and twenty minutes. Sir Wm. Herschel can not tell which is right, or whether both are wrong.[346]
From such imperfect and erroneous calculations astronomers have deduced what they called a law, which holds the same place in nature that the Blue Laws of Connecticut maintain in history; and which like them have imposed upon the credulous. Titius and Bode imagined that they had discovered that, "When the distances of the planets are examined, it is found that they are almost all removed from each other by distances which are in the same proportion as their magnitudes increase." And this law played an important part in introducing the theory of evolution, which, it was alleged, exactly corresponded with such an arrangement. But more accurate calculations and recent discoveries have dissipated the supposed order of progression. Humboldt says of it, it is "a law which scarcely deserves this name, and which is called by Lalande and Delambre a play of numbers; by others a help for the memory. * * * In reality the distances between Jupiter, Saturn, and Uranus approximate very closely to the duplication. Nevertheless, since the discovery of Neptune, which is much too near Uranus, the defectiveness in the progression has become strikingly evident." And Olbers rejects it, as "contrary to the nature of all truths which merit the name of laws; it agrees only approximately with observed facts in the case of most planets, and what does not appear to have been once observed, not at all in the case of Mercury. It is evident that the series, 4, 4+3, 4+6, 4+12, 4+48, 4+96, 4+192, with which the distances should correspond, is not a continuous series at all. The number which precedes 4+3 should not be 4; i. e., 4+0, but 4+1½. Therefore between 4 and 4+3 there should be an infinite number, or as Wurm expresses it, for n=1, there is obtained from 4+2n-2·3; not 4, but 5½."[347] Thus this so-called law is erroneous in both ends, and defective in the middle. Finally it has been utterly abolished by the discovery of the planet Vulcan, which does not correspond to any such law.[348] If the theory of evolution then corresponds to Bode's law, as its advocates alleged, it corresponds to a myth.
About the nebulæ which have played so large a part in the atheistic world building, our astronomers are utterly at variance. Sir John Herschel says they are far away beyond the stars in space. But the Melbourne astronomer, M. Le Seur, suggests that the star Eta and the nebulous matter are neighbors; that the nebulous matter formerly around it, which has recently disappeared, while the star has blazed up into flames, is being absorbed and digested by the star. This has happened before, thirty years ago, to that star. Why may not our sun also absorb and burn up nebulæ. But if so, what becomes of the rings of the nebular theory?
The light of the stars is almost the only medium through which we can observe them, and it would naturally be supposed that astronomers would be at pains to have clear views of light. But the most surprising differences of statement regarding it exist among the very first astronomers. They do not see it alike. Herschel says a Herculis is red; Struve says it is yellow. They dispute about its nature, motion, and quantity. Some astronomers believe the sun to be the great source of light, at least to our system. But Nasmyth informs the Royal Astronomical Society that "the true source of latent light is not in the solar orb, but in space itself, and that the grand function of the sun is to act as an agent for the bringing forth into existence the luciferous element, which element I suppose to be diffused throughout the boundless regions of space."[349] The nature of light is however still as great a mystery as when Job demanded, "Where is the way where light dwelleth?" The undulatory theory of light, now generally accepted, assumes that light is caused by the vibrations of the ether in a plane transverse to the direction of propagation. In order to transmit motions of this kind, the parts of the luminiferous medium must resist compression and distortion, like those of an elastic solid body; its transverse elasticity being great enough to transmit one of the most powerful kinds of physical energy, with a speed in comparison with which that of the swiftest planets of our system is inappreciable, and its longitudinal elasticity immensely greater—both of these elasticities being at the same time so weak as to offer no perceptible resistance to the motion of the planets, and other visible bodies.[350] Is the velocity of light uniform? Or, if variable, is the variation caused by the original difference of the projectile force of the different suns, stars, comets, etc.? or by the different media through which it passes? Arago alleges that light moves more rapidly through water than through air; but Brequet asserts that the fact is just the reverse.[351] Both admit that its velocity varies with the medium. Jacobs alleges that during the trigonometrical survey of India he observed the extinction of light reflected through sixty miles of horizontal atmosphere.[352] How, then, can astronomers make any reliable calculations of the velocity of light reaching us through regions of space filled with unknown media? Newton calculated the velocity of light at one hundred and fifty-five thousand five hundred and fifty-five and five-ninth miles a second; but Encke shows he erred thirty per cent. Other eminent astronomers make the time of the passage of light from the sun all the way from eleven to fourteen minutes, instead of Newton's seven or eight. Busch reckons its velocity at one hundred and sixty-seven thousand nine hundred and seventy-six miles; Draper one hundred and ninety-two thousand; Struve two hundred and fifteen thousand eight hundred and fifty-four. Wheatstone alleges that electric light travels at the rate of two hundred and eighty-eight thousand miles a second; but Frizeau's calculations and measurements give only one hundred and sixty-seven thousand five hundred and twenty-eight for the light of Oxygen and hydrogen.[353] Thus we have a variation of one hundred and twenty thousand miles a second in all calculations of sidereal distances. Humboldt tries to reconcile these differences by the suggestion, that no one will deny, that lights of different magnetic or electric processes may have different velocities; a fact which throws all sidereal astronomy into inextricable confusion, and sets aside all existing time tables on sidereal railroads.