of the threads of the finder; returning then to the large telescope the observer brings one of the points of the micrometer behind one of the principal lines of the star's spectrum. The star to be compared with the first is then brought under the same thread of the finder. If then the micrometer point coincides with a line of the spectrum, this line and the line of the first star's spectrum are evidently identical.

One of the most remarkable results (assuming its correctness) of Secchi's researches, is the observation that two stars-y Cassiopeia, and B Lyræ-show bright lines. In y Cassiopeiæ, for instance, there are several bright lines, but one dominant line in the bluegreen, taking the place of a dark line-the well-known line F of hydrogen-in other star-spectra. The spectra of these two stars are compared by Secchi with the continuous spectrum crossed by bright lines given by magnesium.

The observation would seem to indicate that some stars owe their light in part to the luminosity of their gaseous envelopes, and notably to the presence of burning hydrogen.

Before leaving the subject of spectrum-analysis, we must note the investigation by M. Jansen, of Paris, of the formation of dark lines when light passes through aqueous vapour. He has ascertained that the intensity of certain lines seen in the solar spectrum varies with the amount of moisture present in the atmosphere. By transmitting the light of sixteen gas-burners through a tube filled with steam he reproduced all these lines. Father Secchi appears to have anticipated this discovery.

M. Chacornac has published an interesting paper on Comets. Space will not permit us to deal with the subject otherwise than briefly. He compares together the atmospheres of the sun, of planets, and of comets, under the several conditions of temperature and attraction to which those atmospheres are subject. In the case of planets it is possible that there should be an equilibrium between the attractive force of the planet on the external layers of the atmosphere, and the elastic forces of the layers below; in such a case the atmosphere will have a definite limit. But this clearly cannot be the state of the atmospheres of comets near perihelion, nor of the solar atmosphere. Beyond the bounds of the solar attraction the forces of dilatation exhibit themselves as projective forces acting outwards from the solar periphery. The rays of the solar aureole, in total eclipses of the sun, indicate, by their configuration, the expansive force of gases violently projected into planetary space. To a similar expansive action, acting upon cometary atmospheres, the formation of cometary aigrettes is attributed, while the formation of comets' tails is ascribed to repulsion, produced by the expansive forces of the solar atmosphere.

M. Léon Foucault has devised a new method of solar observa

tion. This consists in covering an achromatic object-glass with a thin film of silver. Such a film, he finds, does not interfere with the definition of the sun. The rays from the less refrangible end of the spectrum are stopped, while the others suffice to exhibit the solar features. M. Leverrier pronounces very favourably on this arrangement, which "seems to promise," he says, more distinct views of the sun than have hitherto been obtained. Other observers find the details of the solar disc slightly "veiled" when thus viewed. It appears to us that there are several objections to the new method, and we should not recommend amateurs to have a valuable objectglass silvered, until something more is heard as to the possibility of restoring the glass to its original state.

But we hear of a contrivance by Messrs. G. and S. Merz of Munich, which seems to promise better views of the sun than have ever yet been obtained." In their solar eye-piece, two pairs of plane unsilvered glass mirrors are so placed, that, by rotating one pair, any part whatever of the sun's light may be intercepted. By this arrangement no false colour is introduced, as with blue, or neutral-tint glasses. Father Secchi says that films are seen with a frosy tint (the colour of the protuberances seen in solar eclipses), in the new ocular, which appeared blue in the common oculars.

The display of meteors (or Humboldt's star-shower, as some name the phenomenon) fully equalled the expectations of the most sanguine. Mr. Dawes considers that upwards of 3,500 fell before 2h. 15m., on the morning of November 14th. Mr. Talmage noted the following numbers in successive intervals of five minutes from 12h. 52m. to 2h. 12m.:-115, 125, 231, 324, 239, 214, 147, 104, 109, 57, 56, 31, 22, 28, 37, 20; showing that the maximum intensity of the shower occurred at about a quarter-past one. While Mr. Hind and M. Du Chaillu (who assisted him) note that "few of the meteors were remarkable for brilliancy or persistence of the trains," Mr. Harris, of Southern-hay, near Exeter, remarks, that at 1h. 15m. a very bright meteor burst, causing a light as bright as daylight, leaving a train which lasted for a quarter of an hour. This is probably the same meteor that is described by Mr. Heath as passing through the Pleiades at 1.30 A.M., and leaving a trail which did not disappear for four minutes. A more satisfactory observation of this "bright, particular star," is that made by Capt. Noble, the astronomer. He notes it as "a splendid one," hour 13h, 20m. 10s. (that is, 1h. 20m.) S. W. of Pleiades, leaving a train which lasted upwards of five minutes by the Observatory clock, and which gradually contracted into a fusiform mass (like 31 M. Andromeda), then into an amorphous one, and finally disappeared behind a cloud. Some of these more permanent streaks, observed in the telescope, were found to be in focus with the stars,

indicating a distance of at least 40 or 50 miles. This observation is due to Mr. Bird, of Birmingham.

While on the subject of meteorites, we may note that the French Academy has received an intimation from Marshal Vaillant, that Marshal Bazaine has found an aerolite in Mexico weighing no less than 860 kilogrammes (considerably more than three-quarters of a ton!)

6

In the Astronomische Nachrichten' (No. 1,606) is an account from C. Behrmann, of Göttingen, of shooting stars coming out of a thick cloud, about 15° from the horizon. The cloud, which covered the sky, was so dense that meteors could not have been seen through it. He considers, therefore, that the stars were driven through the cloud, and came within one-tenth of a mile from the earth. It appears to us that we have read of phenomena strikingly resembling those described by M. Behrmann,-in Arago's Meteorological Essays, under the head globular lightnings.'

The planet Mars will be in opposition on January 10th, 1867, and though less favourably situated as respects distance than in November and December, 1864, or October, 1862, will be well worth careful study. In fact, the presentation of Mars, and the phenomena exhibited upon his surface, vary considerably from opposition to opposition; the complete study of the planet requires that he should be observed at oppositions occurring all round the ecliptic. As respects the oppositions of 1862 and 1864, we refer our readers to Professor Phillips's graphic paper in our volume for 1865. In the approaching opposition the Polar presentation of the planet (as seen in an inverting telescope) will be that shown in Fig. 1.

The outlines of continents and seas here marked in are obtained from the map accompanying the above-named article. By tracing (from Fig. 1) a series of meridian outlines, and

filling in from Professor Phillips' map, our astronomical readers will be enabled to obtain views of the planet at successive intervals of two (Martial) hours. Such views would suffice for comparison with any telescopic views taken near the time of southing, or with views taken at any hour, if due regard be paid to the varying slope of the planet's axis. Towards the end of February the planet (now become much smaller) will appear perceptibly gibbous; his maximum stage of gibbosity, attained early in April, and his apparent disc at that time are exhibited in Fig. 2.

Owing, apparently, to a change of authorities, the apparent diameter assigned to the planet in the 'Nautical Almanac' is larger for January 10, 1867, than for December 1st, 1864. Observers, however, must not expect to find the planet larger; in fact, he will be more than 9,000,000 miles farther from the earth on January 10th, than when in opposition in 1864.

Two more minor planets, the 90th and 91st, have been discovered: the first by Dr. Luther, of Bilk, near Düsseldorf, on October 1st; the second at the Marseilles observatory.

On the 6th of March there will be an annular eclipse of the sun, visible throughout England as a partial eclipse. It will begin at Greenwich at 8h. 17m. A.M., and reach its greatest phase at 9h. 32m. A.M., and end at 10h. 52m. a.m. About seven-tenths of the sun's diameter will be obscured at the time of the greatest phase.

We call the special attention of our readers to the obscuration of the Lunar Crater Linné (on the Mare Serenitatis) observed by Herr Schmidt at Athens. The epoch at which the crater again becomes visible should be carefully noted. This is the same crater that Schröter saw transformed into a dark spot on November 5th, 1788.

PROCEEDINGS OF THE ROYAL ASTRONOMICAL SOCIETY.

Professor Kaiser, of Leyden, in a letter to the AstronomerRoyal, discusses the qualities of the latter's double image micrometer. He expresses a favourable opinion on the instrument, but in one respect astronomers will be disappointed. It has long been known that measurements effected by the best observers with the wire-micrometer present considerable discrepancies. Now, if it had resulted from Professor Kaiser's experiments that the instrument was in fault in such cases, there would have been a prospect of remedying the evil. It appears, however, that the same observer

*The horizontal line through the centre represents the true path of the planet; at the moment of "southing" the slope of the axis will be a few degrees less than in Fig. 1, since the planet's motion in opposition will be carrying him slightly northwards.

using both the wire-micrometer and the double-image micrometer in delicate measurements, obtains results appreciably coincident; so that, as Professor Kaiser remarks, "the discrepancies are far more to be sought in the observers than in the instruments." Referring specially to double-star measurements, he remarks further, that they appear "far too inaccurate for the consequences one will derive from them." The Professor's list of observations serves to exhibit the close approach to coincidence attained by the use of the two instruments, and to afford to observers new estimates of some favourite test-objects.

General Shortrede discusses the effect of the vapour of mercury in depressing the thermometric column. In temperate climates this effect is not often appreciable, and except in very delicate experiments may perhaps be safely disregarded; but in the tropics, or in exceptionally warm weather, the height of the mercurial column is very sensibly depressed from this cause. In India, for instance, General Shortrede found that the true reading, obtained after tilting the barometer so as to condense the vapour, differed from the observed reading before that operation by from 10 to 20-thousandths of an inch, and on one occasion by so much as 023. The tubes were in exceptionally good order, one having been boiled more than twenty times, the vacuum being so perfect that after the tube had been placed some hours in a horizontal position "the mercury, by electrical attraction, would adhere to the top of the tube, and not separate till shaken by tapping," the tube of 32 in. remaining full in this way, at Pana, where the average height is 28 in.!

The subject seems worthy of investigation, since if we would learn the laws regulating the variations of atmospheric pressure, the minutest circumstances affecting the truth of barometric indications must be recognized, so as to be either eliminated or corrected. The Greenwich photographic registrations are evidently liable to be peculiarly affected by a cause of this kind. General Shortrede noticed, indeed, that on one warm day of the past summer the vacuum of the barometer for outside indications (at Greenwich) was studded with minute globules of mercury, derived from the condensation of the mercurial vapour.

Father Secchi sends a drawing of the spectrum of Antares (the Sirius of red stars). Antares attains a sufficient elevation in the latitude of Rome for satisfactory observation with the spectrometer. As might be expected the spectrum (which, by the way, is presented in a reversed position) exhibits a crowding of lines towards the more refrangible (or violet) end, and several spaces clear of lines, or in which lines are more sparsely strewn, towards the red end.

Captain Noble remarks that Jupiter's third satellite reappeared two minutes before the time predicted in the Nautical Almanac.