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 before,) but in a ratio constantly decreasing. It is therefore evident that, ascend as high as we may, we cannot, literally speaking, arrive at a limit beyond which no atmosphere is to be found. It must exist, I argued; although it may exist in a state of infinite rarefaction.
On the other hand, I was aware that arguments have not been wanting to prove the existence of a real and definite limit to the atmosphere, beyond which there is absolutely no air whatsoever. But a circumstance which has been left out of view by those who contend for such a limit, seemed to me, although no positive refutation of their creed, still a point worthy very serious investigation. On comparing the intervals between the successive arrivals of Encke’s comet at its perihelion, after giving credit, in the most exact manner, for all the disturbances due to the attractions of the planets, it appears that the periods are gradually diminishing; that is to say, the major axis of the comet’s ellipse is growing shorter, in a slow but perfectly regular decrease. Now, this is precisely what ought to be the case, if we suppose a resistance experienced from the comet from an extremely rare ethereal medium pervading the regions of its orbit. For it is evident that such a medium must, in retarding the comet’s velocity, increase its centripetal, by weakening its centrifugal force. In other words, the sun’s attraction would be constantly attaining greater power, and the comet would be drawn nearer at every revolution. Indeed, there is no other way of accounting for the variation in question. But again: – The real diameter of the same comet’s nebulosity, is observed to contract rapidly as it approaches the sun, and dilate with equal rapidity in its departure toward its aphelion. Was I not justifiable in supposing, with M. Valz, that this apparent condensation of volume has its origin in the compression of the same ethereal medium I have spoken of before, and which is dense in proportion to its vicinity to the sun? The lenticular-shaped phenomenon, also, called the zodiacal light, was a matter worthy of attention. This radiance, so apparent in the tropics, and which cannot be mistaken for any meteoric lustre, extends from the horizon obliquely upwards, and follows generally the direction of the sun’s equator. It appeared to me evidently in the nature of a rare atmosphere extending from the sun outwards, beyond the orbit of Venus at least, and I believed indefinitely farther. Indeed, this medium I could not suppose confined to the path of the comet’s ellipse, or to the immediate neighborhood of the sun. It was easy, on the contrary, to imagine it pervading the entire regions of our planetary system, condensed into what we call atmosphere at the planets themselves, and perhaps at some of them modified by considerations purely geological; that is to say, modified, or varied in its proportions (or absolute nature) by matters volatilized from the respective orbs.
Having adopted this view of the subject, I had little farther hesitation. Granting that on my passage I should meet with atmosphere essentially the same as at the surface of the earth, I conceived that, by means of the very ingenious apparatus of M. Grimm, I should readily be enabled to condense it in sufficient quantity for the purposes of respiration. This would remove the chief obstacle in a journey to the moon. I had indeed spent some money and great labor in adapting the apparatus to the object intended, and confidently looked forward to its successful application, if I could manage to complete the voyage within any reasonable period. – This brings me back to the rate at which it would be possible to travel.
It is true that balloons, in the first stage of their ascensions from the earth, are known to rise with a velocity comparatively moderate. Now, the power of elevation lies altogether in the superior gravity of the atmospheric air compared with the gas in the balloon; and, at first sight, it does not appear probable that, as the balloon acquires altitude, and consequently arrives successively in atmospheric strata of densities rapidly diminishing – I say, it does not appear at all reasonable that, in this its progress upward, the original velocity should be accelerated. On the other hand, I was not aware that, in any recorded ascension, a diminution had been proved to be apparent in the absolute rate of ascent; although such should have been the case, if on account of nothing else, on account of the escape of gas through balloons ill-constructed, and varnished with no better material than the ordinary varnish. It seemed, therefore, that the effect of such escape was only sufficient to counterbalance the effect of the acceleration attained in the diminishing of the balloon’s distance from the gravitating centre. I now considered that, provided in my passage I found the medium I had imagined, and provided it should prove to be essentially what we denominate atmospheric air, it could make comparatively little difference at what extreme state of rarefaction I should discover it – that is to say, in regard to my power of ascending – for the gas in the balloon would not only be itself subject to similar rarefaction, (in proportion to the occurrence of which, I could suffer an escape of so much as would be requisite to prevent explosion,) but, being what it was, would, at all events, continue specifically lighter than any compound whatever of mere nitrogen and oxygen. Thus there was a chance – in fact, there was a strong probability – that, at no epoch of my ascent, I should reach a point where the united weights of my immense balloon, the inconceivably rare gas within it, the car, and its contents, should equal the weight of the mass of the surrounding atmosphere displaced; and this will be readily understood as the sole condition upon which my upward flight would be arrested. But, if this point were even attained, I could dispense with ballast and other weight to the amount of nearly 300 pounds. In the meantime, the force of gravitation would be constantly diminishing, in proportion to the squares of the distances, and so, with a velocity prodigiously accelerating, I should at length arrive in those distant regions where the force of the earth’s attraction would be superseded by that of the moon.
There was another difficulty, however, which occasioned me some little disquietude. It has been observed, that, in balloon ascensions to any considerable height, besides the pain attending respiration, great uneasiness is experienced about the head and body, often accompanied with bleeding at the nose, and other symptoms of an alarming kind, and growing more and more inconvenient in proportion to the altitude attained. This was a reflection of a nature somewhat startling. Was it not probable that these symptoms would increase until terminated by death itself? I finally thought not. Their origin was to be looked for in the progressive removal of the customary atmospheric pressure upon the surface of the body, and consequent distention of the superficial blood-vessels – not in any positive disorganization of the animal system, as in the case of difficulty in breathing, where the atmospheric density is chemically insufficient for the due renovation of blood in a ventricle of the heart. Unless for default of this renovation, I could see no reason, therefore, why life could not be sustained even in a vacuum; for the expansion and compression of chest, commonly called breathing, is action purely muscular, and the cause, not the effect, of respiration. In a word, I conceived that, as the body should become habituated to the want of atmospheric pressure, these sensations of pain would gradually diminish – and to endure them while they continued, I relied with confidence upon the iron hardihood of my constitution. Thus, may it please your Excellencies, I have detailed some, though by no means all, the considerations which led me to form the project of a lunar voyage. I shall now proceed to lay before you the result of an attempt so apparently audacious in conception, and, at all events, so utterly unparalleled in the annals of mankind.
Having attained the altitude before mentioned – that is to say, three miles and three quarters – I threw out from the car a quantity of feathers, and found that I still ascended with sufficient rapidity; there was, therefore, no necessity for discharging any ballast. I was glad of this, for I wished to retain with me as much weight as I could carry, for the obvious reason that I could not be positive either about the gravitation or the atmospheric density of the moon. I as yet suffered no