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1. He observed the moon when 2 1/2 days old, in the evening soon after sunset, before the dark part was visible, and continued to observe it till it became visible. The 2 cusps appeared tapering in a very sharp, faint prolongation, each exhibiting its farthest extremity faintly illuminated by the solar rays before any part of the dark hemisphere was visible. Soon after the whole dark limb appeared illuminated. This prolongation of the cusps beyond the semicircle, he thinks, must arise from the refraction of the sun's rays by the moon's atmosphere. He computes, also, the height of the atmosphere, which refracts light enough into its dark hemisphere to produce a twilight more luminous than the light reflected from the earth when the moon is up about 32° from the new to be 1356 Paris feet; and that the greatest height capable of refracting the solar ray is 5376 feet.

2. At an occultation of Jupiter's satellites, the third disappeared after having been about 1″ or 2″ of time indistinct; the 4th became indiscernable near the limb; this was not observed of the other two. Phil. Trans. Vol. 82 pr 2. art 16.

The surface of the earth contains 199,512,595 sq. miles. [page 348:]

The quantity of matter in the sun is more than 200,000 times that of the earth. He is 1,410,200 times as big as the earth.

It would require 90,000 moons (filling the whole sky) to equal the light of the sun even in a cloudy day. The altitude of the tides on the moon's surface must be 93 feet, and therefore the diameter of the moon perpendicular to a line drawn from the earth to the moon ought to be less than the diameter directed to the earth by 186 feet.

The supposition of D. de Mairan is that the hemisphere of the moon next the earth is more dense than the opposite one, and hence the same face would necessarily be kept towards the earth.

Juno is free from nebulosity in appearance yet, according to Schroeter, it has an atmosphere more dense than that of any of the old planets of the system — variable atmosphere.

Vesta no nebulosity.

A telescope which magnifies only 1000 times will show a spot on the moon's surface 122 yds diameter. Prof. Frauenhofer of Munich, recently announced that he had discovered a lunar edifice, resembling a fortification, together with several lines of roads.

Schroeter conjectures the existence of a great city on the east side of the moon, a little north of her equator an extensive canal, in another place, and fields of vegetation in another. Herschel has since shown this to be false.

It may be demonstrated from the laws of optics that there exists no physical impossibility to the construction of instruments sufficiently powerful to settle the question of the moon's being inhabited. The difficulty which prevented the great telescope of Herschel from [page 349:] revealing this secret was not so much the want of power in the lens, as of light in the tube, to render objects distinct under such an expansion of the visual rays.

The gravity of a body upon the earth is to that upon the moon as 1 : 0.1677.

The moon's surface contains 14,898,750 sq. miles. The mean eccentricity of the moon's orbit is about 13,200 miles. If the moon have no atmosphere the lunar inhabitants must have an immediate transition from the brightest sunshine to the blackest darkness; and thus must be totally destitute of the benefit of twilight.

The surface of the earth is about 13 times greater than that of the moon. The earth returns 13 times more light to the moon than she receives from it.

The moon is of a phosphorescent substance. This is excited by the action of the sun, and the surface may continue to emit a faint light for some time after sunset — this serving the purpose of twilight. “The pale outline of the old moon,” says Professor Leslie in his Inquiry into the Nature and Propagation of Heat (following the opinion of Riccioli), “is commonly ascribed to the reflection or secondary illumination upon the earth. But if it were derived from that source it would appear densest near the centre, and gradually more dilute towards the edge. I should rather refer it to the spontaneous light which the moon may continue to emit for some time after the phosphorescent substance has been excited by the action of the solar beams” — during conjunction of the sun and moon. Read Brewster's Edition of Ferguson's Astronomy. Brewster does not deny the phosphorescence, but accounts for the eastern rim by the accidental luminousness of that portion of the moon. Make the invisible [page 350:] half of the moon our hell. From one half the moon the earth is never seen at all. From the middle of the other half it is always seen overhead [[over head]] turning round almost 30 times as quick as the moon does. From the circle which limits our view of the moon only 1/2 the earth's side next her is seen, the other half being hid below the horizon of all places on that circle. To her the earth seems to be the biggest body in the universe, for it appears thirteen times as big as she does to us. As the earth turns round its axis, the several continents, seas, and islands appear to the moon's inhabitants like so many spots of different forms and brightness moving over its surface, but much fainter at some times than others, as our clouds cover or leave them. By these spots the Lunarians can determine the time of the earth's diurnal motion, just as we do the motion of the sun; and perhaps they measure their time by the motion of the earth's spots; for they cannot have a truer dia1. Their day w.d then be 24 hours. Her real day and night taken together are as long as our lunar month — a fortnight day, do. night.

Dr. Hooke, accounting for the reason why the moon's light affords no visible heat, observes that the quantity of light which falls on the hemisphere of the full moon is rarefied into a sphere 288 times greater in diameter than the moon, before it arrives at us; and, consequently, that the moon's light is 104,368 times weaker than that of the sun. It would, therefore require, 104,368 full moons to give a light and heat equal to that of the sun at noon. The light of the moon condensed by the best mirrors produces no sensible heat upon the thermometer. Dr Smith in his work on optics, endeavours to show that the light of the full [page 351:] moon is but equal to the 90.900dth part of the common light of day when the sun is hidden by a cloud.

The only equable motion the moon has is that with which she turns round her axis exactly in the same space of time in which she revolves round us in her orbit.

The quantity of matter in the sun is almost 230,000 times as great as the quantity of matter in the earth.

The gravity of the moon towards the sun is greater, at her conjunction than her gravity towards the earth, so that the point of equal attraction where those 2 powers would sustain each other, falls then between the moon and earth.

The point of equal attraction between the earth and the sun is about 70,000 times nearer the earth than the moon is at her change.

The moon sometimes disappears in a clear Heaven so as not to be discoverable by the best glasses; little stars of the fifth and sixth magnitude all the time remaining visible. This phenomenon Kepler observed twice 1580 and 1583, and Hevelius in 1620. Ricciolus and other Jesuits at Bologna, and many people throughout Holland, observed the like April 14, 1642, yet at Venice and Vienna she was all the time conspicuous. Dec. 23, 1703, there was another total obscuration. At Arles she first appeared of a yellowish brown, at Avignon ruddy and transparent, as if the sun had shone through; at Marseilles one part was reddish, the other very dusky, and at length tho’ in a clear sky, she wholly disappeared. Here it is evident that the colours, appearing different at the same time, do not belong to the moon; but they are probably occasioned by our atmosphere which is variously disposed, at different times, for refracting of these or those coloured rays.

Hevelius writes that he has several times found in [page 352:] skies perfectly clear, when even stars of the 6th and 7th magnitude were conspicuous, that at the same altitude of the moon, and the same elongation from the earth, and with one and the same excellent telescope, the moon and its macula do not appear equally lucid, clear and perspicuous at all times, but are much brighter, purer, and more distinct at one time than another. From the circumstances of this observation it is evident the reason of this phenomenon is not either in our air, in the tube, in the moon, or in the spectator's eye, but must be looked for in something existing about the moon.

Cossini frequently observed Saturn, Jupiter, and the fixed stars when approaching the moon to occultation, to have their circular figure changed into an oval one, and in other occultations, he found no alteration of figure at all. In like manner the sun and moon rising and setting in a vaporous horizon, do not appear circular, but elliptical.

Hence it may be supposed that at some times and not at others, there is a dense matter encompassing the moon, wherein the rays of the stars are refracted.

Ricciolus avers the height of St. Catharine to be 9 miles. Ferguson says that some of the mountains of the moon by comparing their height with her diameter, are found to be 3 times higher than the highest on earth.

Keill in his “Astronomical Lectures” finds St. Catharine 9 miles.

Dr. Herschell [[Herschel]] says few exceed 1/2 a mile.

There being no atmosphere about the moon, the heavens in the day time have the appearance of night to a lunarian who turns his back towards the sun.

Mr. Schroeter, of Lilienthal, in the Duchy of [page 353:] Bremen, has endeavoured to establish the existence of an atmosphere from the following observations:

Ap 19, 1787, Dr. Herschel discovered 3 volcanoes in the dark part of the moon. 2 of them seemed to be almost extinct, but the 3d showed an actual eruption of fire, or luminous matter, resembling a small piece of burning charcoal covered by a very thin coat of white ashes: it had a degree of brightness about as strong as that with which such a coal would be seen to glow in faint daylight. The adjacent parts of the mountain seem faintly illuminated by the eruption. A similar eruption appeared on May 4, 1783. On March 7, 1794 a few minutes before 8 in the evening, Mr. Wilkins of Norwich, an eminent architect, observed, with the naked eye, a very bright spot upon the dark part of the moon; it was there when he first looked at the moon. The whole time he saw it, it was a fixed steady light, except the moment before it disappeared, when its brightness increased — he saw it about 5 minutes.

The same phænomenon was observed by Mr. T. Stretton in St John's Sq. Clerkenwell, London, on April 13, 1793, and on Feb. 5, 1794 Mr. Piazzi, astronomer royal at Palermo observed a bright spot on the dark part of the moon near Aristarchus.

The zodiacal light was probably what the ancients called Trabes. Emicant trabes quos docos vocant. Pliny Lib. 2, p. 26.

From a great number of observations Schroeter found the atmosphere of Ceres to be 675 English miles high and he perceived that it was subject to numerous changes (a large dense atmosphere).

The atmosphere of Pallas, according to Schroeter, [page 354:] is to that of Ceres as 2 to 3; it undergoes great changes; 468 miles high.

If we carefully compute the force of gravity in the Moon we shall find that, if a body were projected from her surface with a momentum that would cause it to move at the rate of 8,200 feet in the first second of time and in the direction of a line joining the centres of the earth and moon, it would not fall again to the surface of the moon, but would become a satellite to the earth. Such an impulse might, indeed, cause it after many revolutions to fall to earth.

Mr. Harte calculates 6000 ft. If so, a force 3 times greater than that of a cannon would send a body beyond the point of equal attraction — a force frequently exerted by volcanoes and ( subterraneous steam.

NOTE. — These MS. notes were found in Poe's handwriting among the MSS. in possession of Mrs. W. M. Griswold, Cambridge, Mass. Apparently they are outgrowths of Poe's studies for “Hans Pfaall,” or “Eureka,” with probability inclining to the latter. “Notes on Eureka” is endorsed on the MSS. in a handwriting not Poe's. As may be seen, they are unfinished notes intended to aid in some astronomical work. It is not clear who is meant by “He,” the opening word. The notes are legibly and neatly written with a pencil on both sides of four and one-half sheets (the last being torn) of ordinary memorandum paper. At the end occur three or four interesting signatures of Poe, in ink, evidently scribbled during a reflective moment. — ED.