Let us attempt, at a modest distance, to proceed like Kepler; let us make astronomy without troubling ourselves concerning astronomers. This is the sole means of seizing the luminous point which should guide our steps. * * * * * The movement, in virtue of which every star performs the circuit of heaven in four-and-twenty hours, is incessantly reproduced in a uniform and a constant manner. The acquisition of this first fact, simple as it seems, was a somewhat laborious task, and undoubtedly dates back to a distant antiquity. But now comes another fact, where observation demands the closest mental attention, and which is of a more recent discovery. To comprehend it clearly, let us first call to mind that the moment when the sun crosses the Equator,--whether to return into the northern hemisphere (at the _spring equinox_), or into the southern (at the _autumn equinox_),--is instantaneous. More than one way exists of determining this moment exactly; but here we need not enter upon the subject. Is the interval of time occupied by the sun in travelling from the spring to the autumn equinox equal to the interval which our luminary requires to pass from the autumn equinox to the vernal? 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?