Across the Zodiac - Percy Greg

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the difference between observation through seventy or a hundred miles of terrestrial atmosphere outside the object glass and observation in space. The two discs were perfectly rounded and separately discernible until they touched. Moreover, I was able to distinguish upon one of the darker bands the disc of the satellite itself, while upon a lighter band its round black shadow was at the same time perfectly defined. This wonderfully clear presentation of one of the most interesting of astronomical phenomena so absorbed my attention that I watched the satellite and shadow during their whole course, though the former, passing after a time on to a light band, became comparatively indistinct. The moment, however, that the outer edge passed off the disc of Jupiter, its outline became perfectly visible against the black background of sky. What was still more novel was the occultation for some little time of a star, apparently of the tenth magnitude, not by the planet but by the satellite, almost immediately after it passed off the disc of the former. Whether the star actually disappeared at once, as if instantaneously extinguished, or whether, as I thought at the moment, it remained for some tenth of a second partially visible, as if refracted by an atmosphere belonging to the satellite, I will not venture to say. The bands and rings of Saturn, the division between the two latter, and the seven satellites, were also perfectly visible, with a distinctness that a much greater magnifying power would hardly have attained under terrestrial conditions. I was perplexed by two peculiarities, not, so far as I know, hitherto [5] mentioned by astronomers. The circumference did not appear to present an even curvature.

      I mean that, apart from the polar compression, the shape seemed as if the spheroid were irregularly squeezed; so that though not broken by projection or indentation, the limb did not present the regular quasi-circular curvature exhibited in the focus of our telescopes. Also, between the inner ring and the planet, with a power of 500, I discerned what appeared to be a dark purplish ring, semi-transparent, so that through it the bright surface of Saturn might be discerned as through a veil. Mercury shone brightly several degrees outside the halo surrounding the Earth's black disc; and Venus was also visible; but in neither case did my observations allow me to ascertain anything that has not been already noted by astronomers. The dim form of Uranus was better defined than I had previously seen it, but no marking of any kind was perceptible.

      Rising from my second, or, so to speak, midday rest, and having busied myself for some little time with what I may call my household and garden duties, I observed the discometer at 1h. (or 5 P.m.). It indicated about two hundred terrestrial radii of elevation. I had, of course, from the first been falling slightly behind the Earth in her orbital motion, and was no longer exactly in opposition; that is to say, a line drawn from the Astronaut to the Earth's centre was no longer a prolongation of that joining the centres of the Earth and Sun. The effect of this divergence was now perceptible. The earthly corona was unequal in width, and to the westward was very distinctly brightened, while on the other side it was narrow and comparatively faint. While watching this phenomenon through the lower lens, I thought that I could perceive behind or through the widest portion of the halo a white light, which at first I mistook for one of those scintillations that had of late become scarcely discernible. But after a time it extended visibly beyond the boundary of the halo itself, and I perceived that the edge of the Sun's disc had come at last into view. It was but a minute and narrow crescent, but was well worth watching. The brightening and broadening of the halo at this point I perceived to be due, not to the Sun's effect upon the atmosphere that produced it, but chiefly to the twilight now brightening on that limb of the Earth's disc; or rather to the fact that a small portion of that part of the Earth's surface, where, if the Sun were not visible, he was but a very little below the horizon, had been turned towards me. I saw through the telescope first a tiny solar crescent of intense brightness, then the halo proper, now exceedingly narrow, and then what looked like a silver terrestrial crescent, but a mere thread, finer and shorter than any that the Moon ever displays even to telescopic observers on Earth; since, when such a minute portion of her illuminated surface is turned towards the Earth, it is utterly extinguished to our eyes by the immediate vicinity of the Sun, as was soon the case with the terrestrial crescent in question. I watched long and with intense interest the gradual change, but I was called away from it by a consideration of no little practical moment. I must now be moving at a rate of nearly, if not quite, 40,000 miles an hour, or about a million miles per diem. It was not my intention, for reasons I shall presently explain, ever greatly to exceed this rate; and if I meant to limit myself to a fixed rate of speed, it was time to diminish the force of the apergic current, as otherwise before its reduction could take effect I should have attained an impulse greater than I desired, and which could not be conveniently or easily diminished when once reached. Quitting, therefore, though reluctantly, my observation of the phenomena below me, I turned to the apergion, and was occupied for some two or three hours in gradually reducing the force as measured by the cratometer attached to the downward conductor, and measuring with extreme care the very minute effect produced upon the barycrite and the discometer. Even the difference between 200 and 201 radii of elevation or apogaic distance was not easily perceptible on either. It took, of course, much more minute observation and a much longer time to test the effect produced by the regulation of the movement, since whether I traveller forty, forty-five, or forty-two thousand miles in the course of one hour made scarcely any difference in the diameter of the Earth's disc, still less, for reasons above given, in the gravity. By midnight, however, I was satisfied that I had not attained quite 1,000,000 miles, or 275 terrestrial radii; also that my speed was not greater than 45,000 miles (11–1\4 radii) per hour, and was not, I thought, increasing. Of this last point, however, I could better satisfy myself at the end of my four hours' rest, to which I now betook myself.

      I woke about 4h. 30m., and on a scrutiny of the instruments, felt satisfied that I was not far out in my calculations. A later hour, however, would afford a more absolute certainty. I was about to turn again to the interesting work of observation through the lens in the floor, when my attention was diverted by the sight of something like a whitish cloud visible through the upper window on my left hand. Examined by the telescope, its widest diameter might be at most ten degrees. It was faintly luminous, presenting an appearance very closely resembling that of a star cluster or nebula just beyond the power of resolution. As in many nebulae, there was a visible concentration in one part; but this did not occupy the centre, but a position more resembling that of the nucleus of a small tailless comet. The cloudlet might be a distant comet, it might be a less distant body of meteors clustering densely in some particular part of their orbit; and, unfortunately, I was not likely to solve the problem. Gradually the nebula changed its position, but not its form, seeming to move downwards and towards the stern of my vessel, as if I were passing it without approaching nearer. By the time that I was satisfied of this, hunger and even faintness warned me that I must not delay preparing my breakfast. When I had finished this meal and fulfilled some necessary tasks, practical and arithmetical, the hand of the chronometer indicated the eighth hour of my third day. I turned again somewhat eagerly to the discometer, which showed an apparent distance of 360 terrestrial radii, and consequently a movement which had not materially varied from the rate of 11–¼ radii per hour. By this time the diameter of the Earth was not larger in appearance than about 19', less than two-thirds that of the Sun; and she consequently appeared as a black disc covering somewhat more than one-third of his entire surface, but by no means concentrical. The halo had of course completely disappeared; but with the vernier it was possible to discern a narrow band or line of hazy grey around the black limb of the planet. She was moving, as seen from the Astronaut, very slightly to the north, and more decidedly, though very slowly, to the eastward; the one motion due to my deliberately chosen direction in space, the other to the fact that as my orbit enlarged I was falling, though as yet slowly, behind her. The sun now shone through, the various windows, and, reflected from the walls, maintained a continuous daylight within the Astronaut, as well diffused as by the atmosphere of Earth, strangely contrasting the star-spangled darkness outside.

      At the beginning as at the end of my voyage, I steered a distinct course, governed by considerations quite different from those which controlled the main direction of my voyage. Thus far I had simply risen straight from the Earth in a direction somewhat to the southward, but on the whole "in opposition," or right away from the Sun. So, at the conclusion of my journey, I should have to devote some days to a gradual descent upon Mars, exactly reversing the process of my ascent from the Earth. But between these two periods I had comparatively little to do with either planet, my

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