These longitudes are reckoned, according to the custom of selenographers, from the central first meridian o both ways, in the direction of the preceding, in that of the following edge. As, however, the manner of reckoning has several practical inconveniences and disadvantages, observers of the moon will perhaps not object to a little innovation, which supplies a remedy without interfering with established custom. It is proposed, while retaining or discontinuing at pleasure the employment of selenographical longitudes A, to introduce the use of their complements 90° -λ, and to call the latter "colongitudes." This term and the notation "90°-A," will prevent any misinterpretation or misunderstanding. On the map the colatitude of the preceding edge is o°, that of the central meridian 90°, and that of the following edge 180°. The convenience of the little innovation will perhaps be most readily tested and appreciated by comparing the table previously given with the following, in which the longitudes are supplanted by their colongitudes :—

:

Mercury towards the middle of the month will be well situated for observation, setting an hour after the sun, the interval decreasing.

Venus is too near the sun to be worth observing. She rises after sunset after the 11th.

Saturn is still very low, but may be fairly observed.

ASTRONOMICAL To June, 1872.

Clark, Miss

Morton, Rev. J.

To July, Loder, E. G.

1872.

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BY JOHN BROWNING, ESQ., F.R.A.S.

Read at the Royal Astronomical Society, June 14th, 1872.

From the drawings of Jupiter which I have made since December, 1871, I have selected only four to bring before the notice of the Society. These drawings were made on the following dates :-No. I on December 4th, 1871, at midnight; No. 2 on January 14th, 1872, at 7 p.m.; No. 3 on March 3rd, 1872, at 8.45 p.m.; No. 4 May 5th, 1872 at 9.15 p.m.* The drawings made during the winter months are somewhat deficient in detail, as compared with those made recently; but this I do not doubt is principally the result of the bad definition due to very unsteady air, as the first drawing mentioned, that made on December 4th, contains nearly as much detail as those made recently. The markings are, however, so complex that when the air is unsteady they defy all attempts to draw them accurately. I had some tolerably good views of the planet earlier than December of last year, the tawny color of the equatorial belt seemed to me stronger than I had previously seen it. As, however, a well known observer, who had previously made color observations of Jupiter, did not agree with me, I preferred making continued a series of observations before giving a decided opinion on the subject. Subsequent observations have convinced me that my conclusion was correct, and I have since been fortified in this opinion by the statement of our late President Mr. Lassell. On every occasion when the definition has been good, I have been able to make out light markings flecking the tawny colored surface of the equatorial belt. The drawings I have made do not shew any remarkably symmetrical forms. In several instances I had drawn nearly oval markings or turretted forms on the southern edge of the equatorial belt; but using the highest power

*Two of the four drawings are reproduced in colors in the Monthly Notices. VOL. X.

the night would bear, and watching for fitful intervals of the best definition, I always found these exceedingly regular forms were incorrect, and had to modify them, for this reason. I rather distrust the drawings made on the 3rd of March, the markings on the dark belt south of the equator present forms similar to those we see at times in white cumulous clouds previous to a thunderstorm. I believe that could I have obtained clearer views of the planet, I should not have left these markings quite so regular as they now appear in the drawings. The light belts frequently incline at a considerable angle from the poles towards the equator of the planet. The belt shown on the drawing No. 4, made on May 5th, at 9.15 p.m., G. M. T. makes an angle of nearly 25° with the equatorial belt; a number of shorter markings also about the same angle stretch some distance into the tawny colored equatorial belt; these I at first drew of a turretted form and only very close examination convinced me that they had the inclination I have now given to them. The darker belts have varied from dark warm or cool grey to purple madder or madder brown, but towards the poles of the planets the belts have been usually of a blueish grey, while close to the poles the blue color has been very decided. I have made several observations of the spectrum of the planet, but though I have 12-in. of aperture, I did not find this sufficient to enable me to see more than the dark absorption bands in the red portion of the spectrum, with which most observers are now probably familar. Though I cannot make out any differences in the appearance of the spectrum sufficiently marked to enable me to draw or describe them, yet I strongly suspect a change in the spectrum which a larger aperture giving more light would enable me to bring out.

NOTICE OF A LECTURE BY PROFESSOR G. B. DONATI ON "AURORA BOREALES AND THEIR COSMICAL ORIGIN."

(Concluded from page 148.)

Let us consider only the phenomena of auroras. These are produced almost invariably in the polar regions; since there the action of the terrestial magnetism which may combine with the cosmical, whose actiou never ceases to operate in a certain degree, is more energetic; but if such a degree is by some means augmented, it is evident that there will been corresponding augmentation of the auroral phenomena, which will extend themselves so as to become visible even in places more distant from the poles. Donati proceeds to notice the investigations of Wolf in 1859, and Carrington, in his work published in 1863, on the influence of Jupiter on the number of the sun spots; and of Loomis, who has recently taken into consideration the effect of the combined movements of Jupiter and Saturn, which every ten years (very nearly) are found in a straight line passing through them and the sun. There is also another period. Two revolutions of Saturn round the sun are accomplished in nearly the same time as five revolutions of Jupiter, so that in about 59 years these planets return to exactly the same positions relatively to the sun. These periods have indeed a surprising correspondency with those which we have already remarked as belonging to the greater or less frequency of grand auroras.

* * Science is therefore not adverse to admit that the greater or less development of these phenomena may to a great extent depend upon the simultaneous and combined action of the above mentioned two planets. Donati next refers to a like probable influence in the case of all the other planets, but remarks that the necessary researches to establish this are