of which I had read in history. I have often discussed and debated the vote of the Convention, but I confess to you I see no excuse of state in the execution of such men as Lavoisier, the creator of chemistry, Bailly, the historian of astronomy, André Chenier, the sweet poet, or the condemnation of Condorcet, the philosopher. These have roused my indignation much more than the punishment of Louis XVI. I was intensely interested at being thus a witness of this vanished epoch. But you may imagine how much greater was my surprise, and how much more I was astonished, that I beheld in 1864 events actually present before me which had taken place at the end of the last century.
Quærens. In truth, it seems to me that this feeling of its impossibility ought to have awakened doubt in you. Visions are essentially illusory. We cannot admit their reality even though we see them.
Lumen. Yes, my friend, it was as you say, impossible! Now can you understand my experience in seeing with my own eyes this paradox realised? The common saying is, "One cannot believe one's own eyes." That was just my position. It was impossible to deny what I saw, and equally impossible to admit it.
Quærens. But was it not a conception of your own mind, a creation of your imagination, or perhaps a reminiscence of your memory? Are you sure it was a reality, not a strange reflection from your memory?
Lumen. That was my first idea; but it was so obvious that I saw before me the Paris of '93, and the events of January 21, that I could no longer be in any doubt about it. Besides, this explanation was anticipated by the fact that the old men of the mountain had preceded me in observing these phenomena, and they had seen, and analysed, and conversed on them as actual facts without knowing anything of the history of our world, and were quite unaware of my knowledge of that history. Further, we had before our eyes a present fact, not a past event.
Quærens. But, on the other hand, if the past can be thus merged into the present, if reality and vision can be allied in this way, if persons long since dead can be seen again acting on the scene of life, if new structures and metamorphoses in a city like Paris can disappear and give place to the aspect of the city as it was formerly – in short, if the present can vanish and the past be re-created, what certainty can we have of anything? What becomes of the science of observation? What becomes of deductions and theories? On what solid foundation can we base our knowledge? If these things are true, ought we not henceforth to doubt everything, or else to believe everything?
Lumen. Yes, my friend, these considerations and many others occupied my mind and tormented me, but they did not do away with the reality which I was observing. When I had assured myself that we had present before our eyes the events of the year 1793, it immediately occurred to me that science, instead of conflicting with these facts, ought to furnish an explanation of them, for two truths can never be opposed to one another. I investigated the physical laws, and I discovered the solution of the mystery.
Quærens. What! the facts were real?
Lumen. They were not only real, but comprehensible and capable of demonstration. You shall have an astronomical explanation of them. In the first place, I examined the position of the Earth in the constellation of the Altar as I have told you; I took the bearings of my position relatively to the Polar star and to the Zodiac. I remarked that the constellations were not very different from those we see from the Earth, and that except in the case of a few particular stars, their positions were evidently the same. Orion still reigned in the ultra-equatorial region, the Great Bear pursuing his circular course still pointing to the north. In comparing the apparent movements, and co-ordinating them scientifically, I calculated that the point where I saw the group of the Sun, the Earth, and the planets, marked the 17th hour of right ascension, that is to say, about the 256th degree, or nearly so. I had no instrument to take exact measurements. I observed, in the second place, that it was on the 44th degree from the South Pole. I made these observations to ascertain the star on which I then was, and I was led to conclude that I was on a star situated on the 76th degree of right ascension, and the 46th degree of north declination. On the other hand, I knew from the words of the old man that the star on which we were was not far from our Sun, since he considered it to be one of the neighbouring stars. From these data I had no difficulty in recalling the star that stands in the position I had determined. One only answered to it, that of the first magnitude, Alpha in the constellation of Auriga, named also Capella, or the Goat.
There was no doubt about this. Thus I was certain that I was on one of the planetary worlds of the sun Capella. From thence our Sun looks like a simple star, and appears in perspective to be in the constellation of the Altar, just opposite that of Auriga, as seen from the Earth.
Then I tried to remember what was the parallax of this star. I recalled that a friend of mine, a Russian astronomer, had made a calculation, which had been confirmed, of this parallax. It was proved to be 0,″046. – When I had thus solved the mystery my heart beat with joy. Every geometrician knows that parallax indicates mathematically the distance in units of the magnitude employed in the calculation. I sought then to recall exactly the distance which separated this star from the Earth, in order to prove the accuracy of the calculation. I only needed to find out what number corresponded to 0,″046.2
Expressed in millions of leagues, this number is 170,392,000, and so, from the star on which I was, the Earth was distant 170 billions 392 thousand millions of leagues. The principle was thus established, and the problem was three parts solved. Now, here is the main point, to which I call your special attention, for you will find in it an explanation of the most marvellous realities. Light, you know, does not cross instantaneously from one place to another, but in successive waves. If you throw a stone into a pool of tranquil water, a series of undulations form around the point where the stone fell. In the same way, sound undulates in the air when passing from one point to another, and thus, also, light travels in space – it is transmitted in successive undulations. The light of a star takes a certain time to reach the Earth, and this time naturally depends on the distance which separates the star from the Earth.
Sound travels 340 metres in a second. A cannon shot is heard immediately by those who fire it, a second later by persons who are at a distance of 340 metres, in three seconds by those who are a kilometre off, twelve seconds after the shot at four kilometres. It takes two minutes to reach those who are ten times farther off, and those who live at a distance of a hundred kilometres hear this human thunder in five minutes. Light travels with much greater swiftness, but it is not transmitted instantaneously, as the ancients supposed. It travels at the rate of 300,000 kilometres per second, and if it could revolve, might encircle the Earth eight times in a second. Light occupies one second and a quarter to come from the Moon to the Earth, eight minutes and thirteen seconds to come from the Sun, forty-two minutes to come from Jupiter, two hours to come from Uranus, and four hours to come from Neptune. Therefore, we see the heavenly bodies not as they are at the moment we observe them, but as they were when the luminous ray which reaches us left them. If a volcano were to burst forth in eruption on one of the worlds I have named, we should not see the flames in the Moon till a second and a quarter had elapsed, if in Jupiter not till forty-two minutes, in Uranus two hours after, and we should not see it in Neptune till four hours after the eruption. The distances are incomparably more vast outside our planetary system, and the light is still longer in reaching us. Thus, a luminous ray coming from the star nearest to us, Alpha, in Centaurus, takes four years in coming. A ray from Sirius is nearly ten years in crossing the abyss which separates us from that sun. The star Capella, being the distance above mentioned from the Earth, it is easy to calculate, at the rate of 300,000 kilometres the second, what time is needed to cross this distance. The calculation amounts to seventy-one years, eight months, and twenty-four days. The luminous ray, therefore, which came from Capella to the Earth, traversed space without interruption seventy-one years, eight months, and twenty-four days before it was visible on the Earth. In like manner,
Every one knows that the farther an object is, the smaller it appears. An object which is seen under an angle of one second, is at a distance of 206,265 times its own diameter, whatever it may be; because as there are 1,296,000 seconds in the circumference, the ratio between the circumference and its diameter being 314,159 × 2, it follows that this object is at a distance equal to 206,265 times its own diameter. As Capella sees the semi-diameter of the terrestrial orbit only under an angle 22 times smaller, its distance is 22 times greater. Capella is therefore at a distance of 4,484,000 times the radius of the terrestrial orbit. Future micrometrical measurements may modify these results concerning the parallax of this star, but they cannot change the principle upon which the conception of this work is grounded.
