this velocity, it would take me no more than 161 days to reach the surface of the moon. There were, however, many particulars inducing me to believe that my average rate of travelling might possibly very much exceed that of sixty miles per hour, and, as these considerations did not fail to make a deep impression upon my mind, I will mention them more fully hereafter.
The next point to be regarded was one of far greater importance. From indications afforded by the barometer, we find that, in ascensions from the surface of the earth we have, at the height of a 1000 feet, left below us about one-thirtieth of the entire mass of atmospheric air; that at 10,600, we have ascended through nearly one-third; and that at 18,000, which is not far from the elevation of Cotopaxi, we have surmounted one-half the material, or, at all events, one-half the ponderable body of air incumbent upon our globe. It is also calculated, that at an altitude not exceeding the hundredth part of the earth's diameter—that is, not exceeding eighty miles—the rarefaction would be so excessive that animal life could in no manner be sustained, and, moreover, that the most delicate means we possess of ascertaining the presence of the atmosphere, would be inadequate to assure us of its existence. But I did not fail to perceive that these latter calculations are founded altogether on our experimental knowledge of the properties of air, and the mechanical laws regulating its dilation and compression, in what may be called, comparatively speaking, the immediate vicinity of the earth itself; and, at the same time, it is taken for granted that animal life is and must be essentially incapable of modification at any given unattainable distance from the surface. Now, all such reasoning and from such data, must of course be simply analogical. The greatest height ever-reached by man was that of 25,000 feet, attained in the æronautic expedition of Messieurs Gay-Lussac and Biot. This is a moderate altitude, even when compared with the eighty miles in question; and I could not help thinking that the subject admitted room for doubt, and great latitude for speculation.
But, in point of fact, an ascension being made to any given altitude, the ponderable quantity of air surmounted in any farther ascension, is by no means in proportion to the additional height ascended, (as may be plainly seen from what has been stated be-
