permanency of that journal a matter of certainty. It gives us, indeed, great pleasure to add that, according to a recent editorial announcement of Mr. Hendricks, definite arrangements have been made for its continuance for at least one, and possibly several years.-Analyst, II., No. 12.

ON THE SPECTRA OF THE NEBULE.

Dr. T. Bredichin, Director of the Observatory of Moscow, has lately investigated the spectra of various nebulæ, mostly planetary. The following (the numbers being taken from Herschel's General Catalogue in the Philosophical Transactions for 1864) have almost the same spectrum of three lines, viz., G. C. 4964, 4628, 4234, 4447 (annular nebula in Lyra), 4390, 4510. Regarding the three bright lines in these different nebulæ as identically the same, Bredichin deduces from his measures what he calls the mean spectrum of planetary nebulæ of this class, and he finds it to consist of three lines, A, B, C, of the following wave-lengths:

A=5003.9±1.2; B=4957±1.4; C=4859±3.1.

A and B, as Bredichin remarks, are nearly coincident with the strongest rays of iron (5005 and 4956.5) in the bluishgreen portion of the spectrum.

The nebula 4244 gives a stellar spectrum; the spectra of G. C. 4532 (Dumb-bell), 4373, and 4572 are described. Bredichin speaks of a star in the centre of the disk of 4373, but it is worthy of note that neither Herschel nor Kaiser (who examined this nebula in 1839) describe this star. This deserves examination.-2 G, Nov., 1875, 109.

ON PHYSICAL OBSERVATIONS OF THE PLANET JUPITER.

The physical changes that are seen to take place on the planet Jupiter have of late years attracted an increasing amount of attention by the possessors of large telescopes; and among these Bredichin, of Moscow, has published a series of eighteen photolithographs of the planet as observed by him in 1874. In making these he has employed a telescope of nearly ten inches' aperture, with a magnifying power of 250. He has distinguished six distinct regions, a and ƒ being polar regions, e the equatorial, b and d the tropical, and e the region lying between the north tropical and north polar. The

zone b seems always to have had a color, which has been described as being somewhat green and somewhat blue. A very similar color may be remarked in a thick block of ice. The mean breadth of the equatorial band, c, was 9.7", varying, however, from 7.7" up to 13". Luminous spots were frequently distinguished by him here and there, surpassing in brilliancy all other portions of the planetary disk. The variations of the bands b and c are especially noted by him. -Bullet. Soc. Imp. Naturalistes Moscow, 1874, 185.

THE ATMOSPHERE OF VENUS.

Prof. Watson, of Ann Arbor, in an address to the French Academy of Sciences, giving an account of his observations. of the transit of Venus at Pekin, stated that at the height of about fifty-five miles, or one seventieth of the diameter of Venus, the atmosphere of that planet was liable to cause optical disturbance, such as would prevent the determination of the exact time of the real contact of its limbs with the sun's limbs, and therefore interfere with the determination of the solar parallax.-12 A, XII., 446.

ON THE BRIGHTNESS OF THE SATELLITES OF JUPITER.

Flammarion has made a series of observations of the brightness of the satellites of Jupiter in 1874 and 1875, in which he had in view the especial determination of the relative brightness of each of these, and the determination of their own reflecting powers, as well as the decision whether their brightness is variable, and in what proportions.

Among his observations he cites some showing that there is an atmosphere about each satellite, and, again, that the intrinsic reflecting powers of these four moons is not the same, but varies for each. Thus the fourth satellite is often dull and hazy, and although larger than the first and second, it is generally not so bright. Its surface is also not so white as that of the other satellites. We may then conclude with certainty that its substance, or at least its exterior surface, has less reflective power than that of the other satellites. Its brightness, moreover, varies considerably, and with no definite periodicity, and without any relation to the position of the satellite in its orbit: it is therefore not to any permanent spots on its surface that it owes its changes, but rather

to its own variable atmospheric phenomena. Its brightness varies between the sixth and tenth magnitudes. The dimensions of the four satellites (1, 2, 3, and 4) decrease in the order 3, 4, 1, and 2. The intrinsic brightness decreases in the order 1, 2, 3, and 4. The variability decreases in the order 4, 1, 2, and 3.-6 B, LXXXI., 145, 233.

METEORS OF AUGUST 10TH-11TH, 1875.

The August meteors were observed at Lisbon, in 1875, with the following results:

10-11, 43 meteors; 11-12, 96; 12h-13h, 241; 13h-14h, 331; 14-15, 385; 15-16, 131. Total, 1227 meteors in six hours, or an average of 205 meteors per hour.-22 B, 1875, No. 266.

SPECTRA OF THE GASES CONTAINED IN METEORITES.

Professor A. W. Wright, of Yale College, in 1875 examined spectroscopically the gases derived from the meteorite which fell in Iowa County, Iowa, February 12, 1875. This was of the ordinary stony kind, containing, according to an analysis by Professor J. L. Smith, 12.54 per cent. of nickeliferous iron, and it was investigated in order to determine whether the spectrum of the gases evolved from it by heat would afford any information respecting the recent theories connecting such meteorites with comets.

The spectrum obtained was chiefly that of the carbon compounds, and showed a very close resemblance to the spectra of several of the comets. It was stated at that time that the nature of their gaseous contents establishes a marked distinction between the stony meteorites and the iron meteorites. Professor Wright has lately taken up this inves tigation, with the view of making a more extended comparison of the gases from the two classes, and the results of his examination of several specimens of both classes justifies his former conclusions. All suitable precautions were taken in obtaining and preserving the gases, and portions of the Iowa meteorite were re-examined with the result of confirming previous conclusions.

Professor Wright is still engaged on this research, but he considers the evolution of such large volumes of carbon dioxide as characteristic of the stony meteorites, and the re

lation of these meteorites and their contained gases to the modern theory of comets is certainly of great interest.4 D, April, 1876, 262, and July, 1875.

THE ATMOSPHERE OF VENUS.

Mr. H. C. Russell, government astronomer to New South Wales, in giving an account of the observations made by the various parties stationed there on the transit of Venus, goes into some detail on the subject of the observed halo about the planet Venus, and its possible explanation. Most of the observers state that for some minutes before the first internal contact the whole of the planet's outline could be seen, and three distinct phenomena appeared to be distinguishable: First, a broad ring of light, outside of the planet; second, a bright ring of light around that part of the planet projected on the sky; third, a band of light around the inner edge of the planet, or over its surface. No spots were seen on the planet. The first, or halo, seems to Mr. Russell not likely to be due to any atmosphere. It is a phenomenon, in fact, seen only by some observers and under special conditions. The second, or bright ring, is the most interesting physical feature observed; although at first it would seem to be due to an atmosphere somewhat similar to that of the earth, yet Mr. Russell thinks that a little consideration will show that it can not have such an origin. It is spoken of by all observers as very brilliant, and its actinic power was so great that, although it could appear only as a fine line in the photo-heliograph less than 0.002 of an inch in diameter, it yet had power to affect the chemicals in something less than the 0.004 part of a second. In other words, it was quite as powerful, even more so, than direct sunlight. Mr. Russell thinks that an envelope of some perfectly translucent substance, such as water, would alone suffice to account for all the observed facts. Trans. Roy. Soc. of New South Wales, 1874, 111.

DIAMETERS OF THE INFERIOR PLANETS AS AFFECTED BY

DIFFRACTION.

André, of the Observatory of Paris, has undertaken a research on the diameters of Venus and Mercury as affected by the phenomenon of instrumental diffraction, in connection with the observations of the transit of Venus in 1874, which

is of great interest, as this phenomenon is manifest not only in such observations, but in all cases where a telescope is employed for determining the place of the centre of a body by means of observations on its border or limb. The values of the diameters of Venus and Mercury obtained micrometrically, under ordinary conditions, are always greater than those obtained during a transit, and differ the more according as the aperture of the telescope employed is greater or less. Thus, during the transit of 1874, Mouchez obtained, with an equatorial of eight inches' aperture, the diameter of Venus as 64.38"; the observations of Main, at Greenwich, using a telescope of six and a half inches, and Plummer, of Durham, with about six inches' aperture, gave a diameter of 64.73". This result comes from the fact that the image of a luminous point given by a telescope is not a point, but a disk surrounded by rings alternately dark and bright, whose diameter diminishes with an increase of aperture. The difference of the diameters of Venus or Mercury, obtained by the same instrument during a transit, and under ordinary conditions, should be double, or nearly double, the diameter of the disk of a star (a point) given by that instrument, or at least a quantity of the same order. The observations of Tennant and Main on Venus, and Plummer and Main on Mercury, give 0.724" and 0.602" for this quantity, and theory based on measures of Dawes and Foucault gives for the same quantity 0.854". The practical effect of this is that the observations of the transit of Venus should be reduced to what they would have been provided all the telescopes had the same aperture (in the equipment of the American parties this was provided for by making all the equatorials of the same aperture, viz., five inches), and for this purpose André seeks to determine what he calls the equation of instrumental diffraction. To show the effect of this, he gives the following observations of the first internal contact at St. Paul's Island during the transit of Venus in 1874: