But the reverse is really true. Though the space of four thousand miles (as much, however, as half the diameter of the globe we live on) is an insignificant space, when we are talking of the distances of heavenly bodies; yet, upon this occasion it is worthy to be noted, that the sun and moon, when on or near the horizon, and when they appear largest, are actually four thousand miles further from you than when they are over your heads, or in the middle sky, or zenith, and appear the smallest! Learn this, from the figure I subjoin. When the place в (as Bath or London) has the sun s in its zenith or meridian, the line running from the sun to that place is four thousand miles shorter (that is, a whole semi-diameter of the earth) than What is the zenith? Which is the middle sky? How many miles really nearer to you, are the sun and moon when they are over your head, than when they are on the line of the horizon? when the same place has come round to A, and has the sun in its horizon. A ་ Astronomers, in the meantime, have thought it enough to say that the cause is this: The sky, as they observe, and as is represented in the next figure, does not appear to us as if it were (what it really is) the circular hemisphere M N O P, but like an oval vault only, m n op; and thus, the part at the zenith o seeming much nearer to the eye of the spectator at E, than the horizon at m, the sun seen in the horizon at m will be referred How does Parley show this by means of a diagram or figure? What cause do some astronomers assign for the appearances in question? to a distance E m, and have the apparent magnitude m; while the sun in the zenith will be referred to a distance E o, and have the apparent magnitude which is here drawn at o. But all this is insufficient, because the astronomers are still unable to tell us, why the zenitho appears nearer to the earth than the horizon м? In my Do they say that the vault of heaven does not appear to us as a semicircular arch, but as a semi-oval, or as the half of an ellipsis? Does Parley's second diagram show the zenith and the horizon, and the difference between a true semi-circular arch, and an arch that is elliptical? L preceding figure, I have shown you, that the sun or moon in the zenith are then really nearer to that spot upon the earth from which they are seen, than when they are on or near the horizon; but the puzzle that stops us is, that in the zenith they appear as if they were further off! CHAP. XXVI. OTHER EXPLANATIONS. AN explanation we find offered, why the sun and moon, when on or near the horizon, appear larger than when risen higher into the sky, consists in this; that while they are low in the heavens, or, as it were, near to the earth, we compare them, even without knowing that we do so, with the earth, and with the things upon the earth; and that, while thus compared, they appear larger than when in the upper sky, in the void immensity of which there is nothing to be compared with them for size. An astronomical writer suggests to us, that if we saw a man standing upon a rock in the middle of the sea, we might be enabled to think the rock a large object, through comparing the What other explanations have been offered? What about rocks at sea? |