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 lunation 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 VOL. VIII.-4

Ex

the time of minimum heat in the moon. periments 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 CYCLOPEDIA, 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

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 nebule 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 body passing between us and the central star, giving the variation is produced by the passage of an opaque 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 spectrum. I have employed for this study the comthe hydrogen line in the star and in the compared parison of the direct image of the stars with its own spectrum, but I have found no such quantity of displacement.

A New Comet.-A new comet (II. 1868) was discovered June 13th, by Dr. Winnecke, at Carlsruhe. It was also independently discov ered, 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. In the two more refrangible of these bands, the

light was brightest at the less refrangible end, and gradually diminished toward the other limit of the bands. The least refrangible of the three bands did not exhibit a similar gradation of brightness. These bands could not be resolved into lines, nor was any light seen beyond the bands toward the violet and the red. The author found this cometic spectrum to agree exactly with a form of the spectrum of carbon which he had observed and measured in 1864. When an induction spark, with Leyden jars intercalated, is taken in a current of olefiant gas, the highly heated vapor of carbon exhibits a spectrum which is somewhat modified from that which may be regarded as typical of carbon. The light is of the same refrangibility, but the separate strong lines are not to be distinguished. The shading, composed of numerous fine lines, which accompanies the lines, appears as an unresolved nebulous light. On June 23d the spectrum of the comet was compared directly in the spectroscope with the spectrum of the induction spark taken in a current of olefiant gas. The three bands of the comet appeared to coincide with the corresponding bands of the spectrum of carbon. In addition to an apparent identity of position, the bands in the two spectra were very similar in their general characters and in their relative brightness. These observations were confirmed on June 25th.

The remarkably close resemblance of the spectrum of the comet to that of the spectrum of carbon necessarily suggests the identity of the substances by which in both cases the light was emitted. The great fixity of carbon seems, indeed, to raise some difficulty in the way of accepting the apparently obvious inference from these prismatic observations. Some comets have approached sufficiently near the sun to acquire a temperature high enough to convert even carbon into vapor. In the case of other comets, the author suggests that the difficulty is one of degree only, for the conditions are not known under which even a gas permanent, at the temperature of the earth, could maintain sufficient heat to emit light. The spectrum shows that the color of this comet was bluish green. Considerable difference of color has been remarked in the parts of some comets. Sir William Herschel described the head of the comet of 1811 to be of a greenish or bluish-green color, while the central point appeared of a ruddy tint. The same colors have been observed in other comets. If carbon be the substance of some comets, this substance, if incandescent in the solid state, or reflecting when in a condition of minute division, the light of the sun, would afford a light which, in comparison with that emitted by the luminous vapor of carbon, would appear yellowish or approaching to red. The author refers to the bearing, of these results on certain cometary phenomena, and on the apparent identity of the orbits of the periodical meteors with those of some comets.

The Colors of Saturn.-Mr. John Browning has sent to the Student a report of his recent observations of the colors of Saturn. Examining the planet at midnight, May 9th, with a 123inch instrument and a power of 100, he found no perceptible color. Under a power of 200 to 450, the ring appeared lemon-yellow; the globe, light cinnamon with darker belts scarcely of the same color; Ball's division, purplechocolate; crape ring, same color; pole of the planet, bright azure. May 14th he took another set of observations. The definition was much better than on the 9th, but the colors were not nearly so vivid as on the former date. The north pole of the globe was neutral gray and darker than any other part of the planet, excepting the broad reddish-brown belt immediately north of the equatorial white belt. No part of the globe was pure white. The author remarks that with a 12-inch silvered glass mirror, and a power of 500, the whole ring system produces the impression that it consists of fine lines. Slight inequalities may sometimes be detected in the belts of the globe; more generally they appear quite regular, like the rim of a wheel in rapid motion.

Mr. Huggins hearing that Mr. Browning was engaged on this subject, sent him notes of some of his own observations of Saturn. Mr. H. says that though he can see the colors of Saturn fairly with powers of 500 or 600, yet he finds a power of, at least, 900 necessary to bring out the contrast of the colors in the fullest manner. He warns inexperienced observers that, in consequence of the small altitudes of Saturn, there are prismatic colors seen on it, produced by our atmosphere. From this cause red is seen along the upper edge of the planet in an inverting telescope, and a strong blue at the lower or north edge of the ring, and at the pole. Some time ago, he had considered the crape ring to be of the color of watch-spring; lately he has regarded it as rather more of a grayish blue. Mr. Browning remarks upon this, that the color of the crape ring will vary greatly with the state of an atmosphere. When there is much mist in the air, the color will incline toward red; when the air is clear, the color will become a purer blue.

The author thinks that the different tints on different portions of the rings may be ascribed to the unequal distribution of the countless multitude of minute satellites of which the rings are supposed to be made up. The presence of an atmosphere may further modify their colors. That the rings have an atmosphere, he regards as pretty certain, from the appearance they present when their edges are turned toward us. At such times, nebulous appendages like clouds have been seen upon them. The surface of the globe of Saturn may have a soil of the color of new red sandstone. This color would certainly be strongly modified by cloud-belts, which exist principally at the equator, but extend to the poles. The poles may consist of masses of ice; but it is difficult