A singular question, you reply. Who, indeed, would venture to maintain that the number of days, hours, minutes, seconds, was not exactly the same in the one case as in the other?
Well, the period is not the same; and, therefore, merely to propound this question was a masterpiece of genius. For no ordinary intellectual audacity was needed to doubt the reality of the supposed perfect circle which the sun apparently describes—according to the recognised authorities—in its uniform progress around the globe; that globe believed by all the early astronomers to be imperturbably and everlastingly situated in the centre of their thrice-sacred geometrical figure. This dogma being accepted as infallible, there was every evidence that the two intervals of time, which divided the astronomical year into two moieties, would be of equal duration. It did not occur to the mind of any one of the faithful that the sojourn of the sun, in his circular and uniform movement, might be longer or shorter in the northern than in the southern hemisphere.
What, then, was the name of the audacious innovator who ventured upon putting forth so revolutionary a suggestion?
It was Hipparchus. At least it was he who, confidently relying upon his observations, was the first to affirm that the sun remains longer in the northern than in the southern hemispheres; or, more accurately speaking, that its passage from the spring to the autumn equinox occupies 187 days, while from the autumn to the spring equinox the duration of its course is only 178 days 6 hours (nearly). The year of 365-1/4 days—that is, the Egyptian year, which was universally adopted by the ancient astronomers—was thus discovered to be really divided into two unequal portions, although, theoretically, the sun ought to occupy exactly the same space of time in passing from the spring to the autumn, as from the autumn to the spring equinox.
The fact pointed out and attested by Hipparchus had an influence which he never anticipated on the progress of science. In opposition to all the systems previously designed by man, it followed, in the first place, that the movement of the sun, in relation to a mean movement, must sometimes be accelerated, sometimes be retarded; that the solar arc described in a given time would be greater in winter than in summer.
Astronomers who, trammelled by particular theories, were unable and unwilling to accept of any new light, immediately hastened to raise, as is invariably the case with those who defend a bad cause, a subsidiary and damaging question. They asked whether those inequalities of the sun's movement were real, or only apparent; whether they were more than a mere optical phenomenon, arising from the sun's position vis-à-vis to an observer placed on the earth's surface. And they unhesitatingly pronounced in favour of the appearance, and against the reality.
But man, says an old adage, is always punished after the manner of his sin. Dogmatic and obstinate authority involved our anti-revolutionary astronomers in fresh complications. Such is the case, too, very frequently, in the domain of theology!
Does the sun—the sun as each of us beholds him—ever change his size? Does he ever shrink in his majestic proportions? Is the magnitude of his broad golden disc ever lessened?
Assuredly this new question, which was not less audacious than its predecessor, did not come—there is sacrilege in the thought—from the conservative areopagus of all ancient doctrines; the learned areopagus, or supreme tribunal, which had erected into a dogma the circular orbit and uniform movement of the sun around the earth, the centre of the universe! It could only have been suggested by some unworthy heterodoxical disturber of men's minds,—his name, alas! has not been handed down to us,—who had dared to look upon the heavens, and learn from their bright and beautiful face, without a master, the A B C of science. This "pestilent heretic" had, probably, remarked one of the commonest phenomena connected with the celestial bodies, which astronomers hitherto had not deigned to notice.
Undoubtedly, dear reader, you will have been more than once impressed by the appearance of the solar orb, when obscured in one of those mists so frequent towards the end of autumn:—