Edmond Halley

“ Hence we may reasonably conclude that the Air, or Earth, or both, are sometimes, though but seldom and with great Intervals, disposed to produce this Phænomenon: for though it be probable that many times, when it happens, it may not be observed, as falling out in the Day-time, or in cloudy Weather, or bright Moon-shine: yet that it should be so very often seen at some times and so seldom at others, is what cannot well be that way accounted for. ”

“ Next the Motion of these Beams, furnishes us with a new and, as it seems to me, most evident Argument to prove the diurnal Rotation of the earth: (though that be a matter which, at present, is generally taken by the Learned to be past dispute) For those Beams which rise up to a Point, and did not presently disappear, bat continued for some time, had most of them a sensible Motion, from East to West, contrary to that of the Heavens; the biggest and tallest of them, as being nearest, swiftest; and the more remote and shorter, slower. ”

“ Here I have had no regard to the planet's latitude, both to avoid the trouble of a more intricate calculation, which would render the conclusion less evident, as also on account of the motion of the nodes of Venus not being hitherto discovered, and which can only be duly determined by such conjunctions of the planet with the sun as this. ”

“ Wherefore laying aside all hopes of being able to explain these Things by the ordinary Vapours or Exhalations of the Earth or Waters, we are forced to have recourse to other sorts of Effuvia of a much more subtile Nature, and which perhaps may seem more adapted to bring about those wonderful and surprizingly quick Motions we have seen. ”

“ Helena, about 40 years since, on the stars round the south pole, I happened to observe, with the utmost care, Mercury passing over the sun's disk: and contrary to expectation, I very accurately obtained, with a good 24-foot telescope, the very moment in which Mercury, entering the sun's limb, seemed to touch it internally, as also that of his going off; forming an angle of internal contact. Hence I discovered the precise quantity of time the whole body of Mercury had then appeared within the sun's disk, and that without an error of one single second of time ”

“ And whilst we regarded the Heavens with attention, we perceived a very thin Vapour to pass before us, which arose from the precise East part of the Horizon, ascending obliquely, so as to leave the Zenith about 15 or 20 Degrees to the Northward. But the swiftness wherewith it proceeded was scarce to be believed, seeming not inferiour to that of Lightning; and exhibiting, as it past on, a sort of momentaneous Nubecula, which discovered it self by a very diluted and faint Whiteness; and was no sooner: formed, but before the Eye could well take ‘it, it was gone, aid left no Signs behind it. ”

“ For, in the neighbouring places Venus's parallax will protract the duration of the transit, and make it at least 6 minutes longer; because while the sun seems to tend under the pole from west to east, these places on the earth's surface will seem to be carried with a contrary motion towards the west, that is, with a motion conspiring with the proper motion of Venus; consequently Venus will seem to move slower within the sun's disk, and continue longer on it. ”

“ Another consideration has made these authors enlarge this distance a little more: for since the moon's diameter is rather more than a quarter of the earth's diameter, if the sun's parallax be supposed 15 seconds, the body of the moon would be larger than that of Mercury, viz. a secondary planet larger than a primary one, which seems repugnant to the regular proportion and symmetry of the mundane system. ”

“ And if fuch a Medium should be thus inclosed within us; what should hinder but we may be allowed to suppose that some parts of this lucid Substance may, on very rare and extraordinary Occasions, transude through and penetrate the Cortex of our Earth, and being got loose may afford the Matter whereof this our Meteor consists. This seems favoured by one considerable Circumstance, viz. that the Earth, because of its diurnal Rotation, being necessarily of the Figure of a Flat Spheroid, the thickness of the Cortex, in the Polar Parts of the Globe, is considerably less than towards the Equator ”

“ And indeed I would have several observations made of the same phenomenon in different parts, both for further confirmation, and lest a single observer should happen to be disappointed by the intervention of clouds from seeing what I know not if those either of the present or following age shall ever see again; and upon which, the certain and adequate solution of the noblest, and otherwise most difficult problem depends. Therefore again and again, I recommend it to the curious strenuously to apply themselves to this observation. ”

“ Yet was it no Cloud, but only the serene Sky more than ordinary pure and limpid, so that the bright Stars shone clearly in it, and particularly Cauda Cygni then very low in the North; the great Blackness manifestly proceeding from the Neighbourhood of the Light which was collected above it. For the Light had now put on a Form quite different from all that we have hitherto described, and had fashioned it self into the Shape of two Laminæ or Streaks, lying in a Position parallel to the Horizon, whose Edges were but ill terminated. ”

“ Hence also it is manifest how that wonderful Corona that was seen to the Southwards of the Vertex, in the Beginning of the Night, and so very remarkable for it’s tremulous and vibrating Light, was produced; to wit, by the Concourse of many of those Beams arifing very high out of the circumjacent Regions, and meeting near the Zenith: the Effluvia whereof they consisted mixing and interfering one with another, and thereby occasioning a much stronger but uncertain wavering Light. ”

“ And as Earthquakes happen with great Uncertainty, and have been sometimes frequent in Places, where for many Years before and after they have not been felt; so These, which we might be allowed to suppose produced by the Eruption of the pent Vapour through the Pores of the Earth, when it is not in sufficient Quantity, nor sudden enough to shake its Surface, or to openit self a Passage by rending it. ”

“ By which means, the one overtaking the other, they would times seem to meet and jostie ; and at other times to separate, and fly one another. But this Motion was only Optical, and occasioned by the Eye of the Spectator being carried away with the Earth in to the East; whilst the exceeding rare Vapour of which those Beams did consist, being, as I take it, railed far above the Atmosphere, was either wholly left behind, or else followed with but part of its Velocity, and therefore could not but seem to recede and move the contrary Way. ”

“ That supposing the Earth to be concave, with a lesser Globe included, in order to make that inner Globe capable of being inhabited, there might not improbably be contained some luminous Medium between the Balls, so as to make a perpetual Day below. ”

“ But for about forty five Degrees on either side, from B to G or I, and from A to H or K, they will form themselves into Curves, more and more crooked as they are remoter from the Poles; aad withall more and more oblique to the Surface of the Stone: as our Figure truly represents, and as may readily be shewn by the Terrella and Apparatus for that Purpose in the Repository of the Royal Society Hence it may appear how this exceeding subtile Matter revolves ”

“ But these are the principal Phænomena; of whose Causes I should have more willingly and with more certainty given my Thoughts, if I had had the good luck to have seen the whole from Beginning to end; and to have added my own Remarks to the Relations of others; and especially if we could by any means have come at the Distances thereof. ”

“ Nor was this a single. appearance; but for several Minutes that we regarded: it, about six or seven times in a Minute, the same was again and again repeated; these Waves of Vapour (if I may be allowed to use the Word) regularly succeeding one another, and, as we guest, at intervals very nearly equal; all of them in their Ascent producing a like transient Nubecula. ”