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the south (the sixth ridge of Schroter). On that date there was not the slightest indication of a shallow crater, nor the least appearance in the surface round the cone which might be considered indicative of its becoming a white spot as the sun rose above it. The terminator was a little east of the cone, and the next ridge beyond the cone toward the east was becoming visible. Mr. Huggins, Mr. Carpenter, and Mr. Penrose observed Linné the same evening, with the same results obtained by Mr. Birt. Mr. Carpenter also gives the crater opening on the cone. Rev. T. W. Webb made observations confirming those of the other gentlemen. The portion of the Mare Serenitatis on which the cone was seen is so surrounded by ridges as to be easily taken for a large shallow crater, and it may be that some of the discordances between observers may be thus explained. Mr. Birt remarks that we are greatly ignorant of the true nature of the moon's surface. The extent of our knowledge appears to be of a twofold character: First, we perceive differences of color and brightness, from which we infer that the surface consists of different materials reflecting different degrees of light, and also of tint. Second, the presence of shadow reveals to us manifest irregularities of surface as regards level, elevation, and depression. With the nature of the surface beyond these two characteristics we are unacquainted, and can only trace out slowly certain analogies with phenomena that are familiar to us on the earth's crust.

Other supposed Changes in the Moon.-Herr J. F. Julius Schmidt, Director of the Athens Observatory, notified Mr. Birt, in June, of his discovery of another supposed change on the moon's surface. The region of the phenomenon is situated easterly, near Alpetragius. At this point Mädler in his Atlas has a crater almost a mile in diameter, and says, "in the farthest east shines also, with a light of 8°, the small crater d." This crater d, Herr Schmidt proceeds to say, now no longer exists, but, in

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its place is a round spot of light more than two miles broad, extremely brilliant, which has quite the character of the spot Linné and of the few others of this kind which are found on the moon. The small crater south of d, which Mädler gives, is still distinctly visible. Schroter has nothing about this spot of light. Lohrmann's (unedited) plate gives a very large spot, almost 2° in magnitude, and a very small hill inside of it. Herr Schmidt sent to Mr. Birt three sketches, the first from Mädler, the second from Lohrmann, and the third his own. Mr. Birt took an early opportunity to examine the region of the supposed change. Schmidt's sketch was found to be a faithful representation of the spot, with perhaps the exception of the white spot being better defined and in more striking contrast with the surface near it. Two friends, who were with Mr. Birt at the time, bore testimony to the accuracy of Schmidt's sketch. Mr. B., of course, failed to identify the features depicted by Lohrmann and Mädler.

Mr. W. R. Birt communicated a paper to the meeting of the Manchester Literary and Philosophical Society, giving an account of a new variable spot on the moon's surface, which exhibited similar phenomena to those of the crater Linné. The observations were made by Rev. W. O. Williams, of Pwllheli, who had undertaken the examination of a zone on the moon's surface, of 2° of latitude, from 4° to 6° south. The spot in question was situated on the southwestern side of the ridge forming the northeastern boundary of Hipparchus. Its diameter is 5°.94, and magnitude 0°.37, the diameter of Dionysius being regarded as unity. On De la Rue's photograph, February 22, 1858, it appears as a spot of about 4° of brightness. It is not so bright as Linné, which is about 5°. On Rutherford's photograph it appears brighter than in De la Rue's, namely, 5°-Linné being 6° in the same photograph. The observations alluded to by Mr. Birt are as follows:

Ph. A bright spot.
Ph. A bright spot.
Obs. A shallow crater.
"A very bright spot.

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YEAR.

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1865

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1867

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"A faint shallow crater. "Drawn as a crater.

Crater very conspicuous, with a small central cone casting a shadow.

"Very bright, a streak of interior shadow

on the west.

"A bright patch of light, streak of shadow scarcely discernible."

"Very bright.*

66

A whitish spot, no trace of a crater. "A whitish spot, no crater.

Mr. Baxendell states that on the night of the 3d of January, 1868, he had an opportunity of examining the spot referred to by Mr. Birt, with Mr. Gladstone's equatorially mounted

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point to the east, which he considered to be the highest point of the ridge.

*On these occasions Mr. Williams saw a small bright

ers from 60 to 250. It was then a well-marked though shallow crater, having a diameter about three-fourths of that of Beer and Mädler's Hipparchus F. The shadow of the western wall was very conspicuous on the floor of the crater.

In a paper read before the British Association, Baron von Mädler makes a few suggestions to moon-observers. He calls attention to certain straights of light which only show themselves in high sun illumination; of these nothing is known, except that they are by no means elevations. Ridges of only 500 feet high are to be recognized through this shadow near the light edges; but these straights never show the smallest shadow, and vanish in the vicinity of the light edges. They proceed in a radiating manner from single bright Ringmountains, especially from Tycho, Copernicus, Kepler, Byrgins, Aristarchus, and Olbers; from some other Ring-mountains they proceed only from one side, as from Menelaus and Proclus. By a superficial observation they may easily be confounded with the mountain veins, but an attentive examination will remark essential differences between them. The easiest to observe is the light straight which divides the Mare Serenitatis almost equally in halves. He had observed this several times for shadow, but could never detect the smallest. The author alludes to the rills on the moon's surface, as objects whose variability, probably, does not depend on our atmosphere, but is to be referred to real changes. He had sought for two years in vain for the southwest continuation of the Ariadæus rill, though its existence came to his knowledge from other quarters-till, unexpectedly, he obtained sight of it in 1833. He remarks that it is advisable to observe on the same evening, not merely a single rill, but many somewhat similar ones; for as the earth's atmosphere must exercise a like effect upon them all, so would a perceptible variation present us with a hint for further investigations.

Heat given out by the Moon.-Mr. J. P. Harrison, in a paper read before the Royal Astronomical Society, takes the ground that the heat acquired by the moon, and radiated to the earth, is what Prof. Tyndall calls "dark heat," or what would be almost wholly absorbed by our atmospheric vapor. This would raise the temperature of the air above the clouds, increase evaporation from their surface, diminish their density, raise them to a higher elevation, and under favorable circumstances disperse them. In either case, a sensible fall would take place in the temperature of the air near the ground. This occurs at the period of lanation when the moon has acquired the greatest amount of heat it can receive from the sun, which is when the half-moon then illuminated has been subjected to solar radiation for about 265 hours, or at the third or last quarter. Opposite results will occur at

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the time of minimum heat in the moon. Experiments to test the heat of the moon have been made by Prof. C. P. Smyth, at Teneriffe. He found that it amounted to no more than would be given out by the heat of a waxcandle at a distance of fifteen yards. Mr. Harrison shows that this was not the right time to have expected to discover heat from the moon; that at the time when most heat was really given out, the effect upon the earth's surface was, that a lowering of the temperature was produced. Mr. Harrison refers to the tabulated results of temperature at Oxford, Greenwich, and Berlin, taken for several years, which agree in proving that, at the time when by calculation the moon must have acquired the greatest heat, the average temperature of the earth's surface was lower, accompanied by a dispersion of cloud.

Solar and Planetary Tables.-The Royal Astronomical Society of England, at their annual meeting in February, awarded the gold medal to M. Le Verrier for his solar and planetary tables, which include Mercury, Venus, the Earth, and Mars, and have superseded others for calculating the places referred to.

Secular Variation of the Elements of the Earth's Orbit.-Mr. John L. Stockwell communicated to the American Journal of Sciences for July an interesting paper on the "Secular Variations of the Elements of the Earth's Orbit" (see ANNUAL CYCLOPÆDIA, for 1867, art. ASTRONOMICAL PHENOMENA AND PROGRESS). Mr. Stockwell furnished a table, appended hereto, based upon data and formulas more fully given in his treatise on the "Secular Equations of the Moon's Mean Motion." The materials used in the preparation of the formulas are those used in the construction of the American Ephemeris and Nautical Almanac, with the exception of the mass of the earth, which has been increased to 1. The contents obtained by Mr. Stockwell differ somewhat from those given by Le Verrier in his Memoir on the Secular Inequalities of the Seven Principal Planets, not only on account of the disturbing influence of the planet Neptune, which had not been discovered at the time of his investigation, but also on account of the improved values of the masses and elements of the other planets. The superior limit of the eccentricity of the earth's orbit, which Le Verrier gives as equal to 0.07775, should be reduced to 0.06939, and an increase of the mass of the earth, corresponding to the latest determinations of the solar parallax, would reduce the value of the superior limit still more.

In Mr. Stockwell's treatise on Secular Equations, etc., already referred to, he gave a table and chart showing the eccentricity of the earth's orbit during the period of a million of years; and the table here presented is merely an extension of the former one. The first date in the following table corresponds to 1,175,566 years before the year 1850, or to 1,100,000

years before the epoch of the integral in the treatise mentioned. From Mr. Stockwell's calculations, it appears that, if at any epoch there is a maximum or minimum of any given magnitude, in 1,450,000 years before or after that epoch, there will be a corresponding maximum or minimum. A computation similar to this, prepared by Mr. James Croll, and published in the Philosophical Magazine, for February, 1867, was based upon Le Verrier's formulas: Table showing the Elements of the Earth's Orbit during a period of one million of years.

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interpreted by calculators. He has found that when those observations are compared together, which are really comparable, the result is that the sun's horizontal parallax is 8".91, very closely agreeing with that derived from the observations of Mars, in 1862. The mean distance of the sun, deducible from this parallax, is 91,740,000 miles. That which is deducible from the opposition of Mars (sun's parallax 8".94) is 91,430,000. The transit of Venus in 1882 will afford a most favorable opportunity to estimate the distance of the sun; better than the transit which will occur in 1874.

Asteroids.-Reported discoveries of new minor planets during the year brought up the whole number now known to 106. M. Coggia, at Longchamp, Marseilles, discovered No. 96 February 17th. On the same night, M. Tempel, of Marseilles, added another to the list, No. 97, and named it Clotho. M. Tempel requested the finders of the next two planets to accept for them the names Lachesis and Atropos, in order that the three sister Parcæ might together complete the first hundred of the planets. When Le Verrier announced to the French Academy of Sciences the discovery of planet 96, M. Delauny took exception to the reprehensible practice of withholding the names of the subordinates in government observatories 0.04341 by whom discoveries of comets and planets may 0.04273 0.03865 be made. He added that the discoverer of 0.03199 planet 91 (Egina) was M. Borelly. Profes0.02380 0.01553 sor Watson has named two planets discovered by him in 1867 as follows: 93, Minerva, and 94, Aurora. To the United States belongs the honor of finding the majority of the new planets of 1868. On the 18th of April, Professor C. H. F. Peters, of Clinton, N. Y., discovered 98. Its situation was reported as follows:

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The planet was then of the 13th magnitude. Professor James C. Watson, of Ann Arbor, 200 81 0.04204 Mich., discovered No. 100 July 11th, and named it Hecate. It shone like a star of the 10th magnitude. 101, and gave it the name of Helena. EleOn the 15th of August he discovered ments of the two planets furnished by Professor Watson to the American Journal of Science are as follows:

Distance of the Sun.-The problem of the sun's distance has lately been reinvestigated by Mr. Stone, first assistant of the Royal Observatory, Greenwich. He has found that previous calculators, including Encke, have fallen into some mistakes in their use of the recorded observations of the transit of Venus. In consequence of the effects of irradiation of the sun's light as the planet passes on and off his disk, the phenomenon is somewhat complicated, and discoverers made use of different terms in describing it. Some of these expressions, according to Mr. Stone, have been mis

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of compound prisms, which gives a dispersive power equal to nearly seven prisms of 60° of dense flint glass, Mr. Huggins has been making a new series of observations on heavenly bodies. His conclusions with regard to Sirius are specially interesting. He is of the opinion that the substance in that star, which produces the strong lines in the spectrum, is hydrogen; also that the aggregate result of the motions of the star and the earth in space, at the time the observations were made, was to degrade the refrangibility of the dark line in Sirius by an amount of wave length equal to 0.109 millionth of a millimetre. Taking the velocity of light at 185.000 miles per second, and the wave length of the dark line at 486.50 millionths of a millimetre, the observed alteration in period of the line in Sirius will indicate a motion of recession, between the earth and the star, of 41.4 miles per second. At the time of observation, that part of the earth's motion which was in the direction of the visual ray was equal to a velocity of about twelve miles per second from the star. There remains unaccounted for, a motion of recession from the earth amounting to 29.4 miles per second, which the author feels entitled to attribute to Sirius. He refers to the inequalities in the proper motion of Sirius, and remarks that, at the present time, the than its average amount by nearly the whole proper motion of the star in declination is less of that part of it which is variable, which circumstance may show that a part of the motion of the star is now in the direction of the visual ray.

Observations of Nebula.-Mr. Huggins has applied his new spectroscope with some success to the study of a large number of nebulæ. About one-third of them give a spectrum of bright lines. The spectrum of the great nebula in Orion was carefully examined by several methods of comparison, with the spectra of terrestrial substances. The coincidence of the lines with those of hydrogen and nitrogen, remained apparently perfect with an apparatus in which a difference in wave length of 0.0460 of a millimetre would have been detected. These results increase greatly the probability that the lines are emitted by nitrogen and hydrogen. Mr. Huggins regards it as a question of much interest whether the few lines of the spectra of the nebulæ represent the whole of the light emitted by those bodies, or whether those lines are the strongest lines of their spectra which have succeeded in reaching the earth. He supposes that, since the nebulae are bodies that have a sensible diameter, and in all probability present a continuous luminous surface, no lines have been extinguished by the effect of the distance of the objects from us; and he suggests that, if we had reason to believe that the other lines which present themselves in the spectra of nitrogen and hydrogen were quenched on their way to us, we should have to regard their disappearance as an indication of a power of extinction residing in cosmical

space, similar to that inferred from theoretical considerations by Chéseaux and afterward supported, on other grounds, by Olbers and the elder Struve. The author concludes that, at the time of his observation, the nebula of Orion was not receding from the earth with a velocity greater than ten miles per second; for this motion, added to the earth's orbital velocity, would have caused a want of coincidence of the lines of the spectrum that could have been observed.

Suspected Change in a Nebula.-The Rev. H. Cooper Key, of England, has been making observations on the nebula, 45 Herschel, IV Germinorum, with a silvered glass speculum of eighteen-inch aperture, and ten feet focal length, using an eye-piece giving a power of 510. This nebula presented to the Herschels a uniform nebulous disk, with a stellar centre; Lord Rosse saw one ring only; in Mr. Key's telescope, two rings were distinctly visible. Mr. Huggins considers the observation important, as showing a definite change in these objects; the central star of the nebula gives a continuous spectrum, and possibly the luminous haze surrounding it also; but of that Mr. Huggins is not so certain, the difficulty of getting spectrum observations of such faint objects is so great.

Stellar Spectra.-Father Secchi has communicated to the French Academy of Sciences some further observations on stellar spectra, made by means of a new spectroscope, with a cylindrical achromatic eye-piece. He concludes that, 1st, red stars have generally spectra of the third type; when the color is pale, it may be referred to an intermediate place between the second and third; 2d, a great number of these stars have their spectra perfectly resolvable into columns which are afterward themselves resolvable into finer lines. There are many others that cannot be resolved into secondary lines, on account of the faintness, but of which the principal lines indicate the type; 3d, the stars which cannot be referred to the three established types are very rare. Some of the author's speculations and suggestions are interesting. He says:

We have, therefore, without doubt, in the heavens a grand fact, which is the fundamental distinction of the stars in a small number of types, which opens the field to very many cosmological important speculations.

Secondly, another grand fact, which was brought out from those researches, was, that the stars of the same type are crowded occasionally in the same space of the heavens, so the white stars are thickly gathered in the Leo, in the Ursa Major, in Lyra, Pleiades, etc., while the yellow ones are very frequent in Cetus, in Eridanus, Hydra, etc. The region of Orion is very remarkable for having all through, and in the neighborhood, green stars of the first type, but with very narrow lines and with scarcely any red color. It seems that this particular kind of star is seen through the great mass which constitutes the great nebula of Orion, whose spectrum may contrast with the primitive spectrum of the stars. Sirius is perhaps too near us to be affected by this influence. The distribution of stars seems to indicate in space a particular distri

bution of matter or of temperature in the different regions.

Thirdly, all the spectra of the third and fourth type belong to variable stars. The representative of these is the wonderful (Mira) Ceti. This has been carefully examined and found that, even when it is only of the seventh magnitude, it has the same specbright lines; a Orion is in the same condition, a trum as the typical, but only reduced to its few Tauri or Aldebaran, and Antares, this year appeared to be smaller and of a more red hue than in the past year, and in the first appeared traces of columns which were not seen the year before; so that it is evident that the change of these stars depends on a periodi cal change which happens in their atmosphere. It is not so, however, with Algol, which has the very same spectrum of the first class or type in every stage of greatness; which induces me to believe that there the variation is produced by the passage of an opaque body passing between us and the central star, giving thus an example of eclipse of a fixed star, by his own obscure planet.

Finally, a very delicate question I propose to myself to be resolved by spectral analysis; this consists from the displacement of the lines, which ought to in ascertaining whether the star has a proper motion take place in the spectrum by the combined motion of the star and the propagation of light. From this new kind of aberration it would be easy to ascertain if a star has a motion whose velocity should be five times that of our earth around the sun. The star a of Lyræ, examined in this manner, has not given any such displacement, so that it appears not to have such a motion. In some other stars I have found that there is a little displacement, as in Ursa Majoris, but this seems especially due to the different breadth of the hydrogen line in the star and in the compared spectrum. I have employed for this study the comparison of the direct image of the stars with its own spectrum, but I have found no such quantity of dis placement.

A New Comet.-A new comet (II. 1868) was discovered. June 13th, by Dr. Winnecke, at Carlsruhe. It was also independently discovered, the same night, at the Marseilles observatory. The next night, several astronomers, to whom the discovery had been communicated, observed the comet, and described it as very bright and having a tail. On the 20th, the tail was more than 3° in length. About that time the comet was just visible to the naked eye, and, when brightest, was comparable to a star of the fifth magnitude. It passed its perihelion, June 26th; its distance from the sun being then about six-tenths of that of the earth. It was nearest the earth, June 30th, and was then within about 56,000,000 miles of us. Early in July it gradually ceased to be visible.

The Spectrum of Comet II., 1868.-Mr. Huggins, the industrious and skilful observer of the spectra of astronomical bodies, made a careful study of the spectrum of comet II., of the past year. The results he communicated to the Royal Society in July. He describes the appearance of the comet in the telescope, June 22d, as a nearly circular corona, which became rather suddenly brighter toward the centre, where there was a nearly round spot of light. A tail was traced for almost a degree. The light of the comet, examined with a spectroscope, furnished with two prisms of 60°, was resolved into three broad bright bands. the two more refrangible of these bands, the

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