THE PLANETS FOR AUGUST.

Mercury may be seen at the beginning of August, setting after the Sun, about half-past 8 o'clock. It is in the constellation Leo.

1st R.A. 10 26 8

11 19 34

Dec. N. 9 40

S. 028

Diameter 6" 4

10" 4

31st Venus continues to be a brilliant object in the early mornings, rising between 1 and 2 o'clock during August. It passes from Taurus to Cancer during the month.

1st R.A. 5 35 23

31st

7 55 49

Dec. N. 20 291

22 19 48

Illuminated portion of the disc of Venus=0·638.

Mars is practically invisible during August.

Jupiter continues in Ophiuchus, and is a brilliant object during the evenings of the month, but still very low in declination.

31st 37" 2 Saturn may still be observed, but is passing away for the season. 1st R.A. 13 34 52 Dec. S. 7 181 Diameter 15"0

31st Dimensions of ring-Outer major axis, 37"0; Outer minor axis, 9′′3. Uranus is now visible after midnight.

Neptune may also be seen, a little north of the equator, in the constellation Pisces.

The following are the minor planets which will arrive at opposition this month. Full particulars will be found in the Supplement to the Nautical Almanac for 1868:

OCCULTATIONS observed at Teignmouth, by G. J.Walker, Esq.:July 3, 8 Libræ, Immersion, 9 h. 27 m. 53 s.; Teignmouth mean time. a2 Libræ, do. 9 41

Both stars flashed out instantaneously, without any previous diminution of brightness.

INSTRUMENTS, &c. FOR SALE.

These Notices, which are restricted to three lines each, are inserted free of charge to subscribers: applications respecting prices and other particulars to be made to the Editor, with a stamped envelope for reply, without which no answer can be sent.-For Advertisements with prices and more complete details, a small charge will be made. N.B.-It is particularly requested that we may be informed when instruments are disposed of, in order that the notice may be withdrawn, and fruitless applications prevented.

[29]

Achromatic Refractor, 7 in. aperture, 9 ft. focus, by Troughton & Simms; 5 celestial and I terrestrial eye-pieces; on large garden Equatorial stand, with patent steadying rods, &c. [54] Equatoreal Telescope, 5 ft. focus, 4 in. aperture; powers 60, 340, and 450, on extra stout mahogany tripod stand, steadyingrods, levels, large finder, &c., complete. [18] Achromatic Refractor, 4 ft. focal length, 3 in. clear aperture, by Wray; with two celestial and one terrestrial eye-pieces, on garden stand. [46] Achromatic Refractor, 4 ft. focal length, 3 in. aperture, on brass tripod stand, with achromatic finder, 3 celestial and 3 terrestrial eye-pieces, &c. [20] Newtonian Reflector, 7 ft. focus, 7 in. aperture, 8 eye-pieces, powers from 30 to 360, Equatoreally mounted. Transit Instrument, 5 ft. focus, 3 in. aperture, Ys fitted with agates, for mounting on stone piers. Equatorial Stand, adapted for a 5 or 6 ft. telescope: 13 in. circles divided on silver, reading to 10" of space and 4s. of time.-Has never been used. [55] Equatorial Stand, for a 4 or 5 ft. telescope; 8 in. circles, divided on silver, with verniers and microscopes; tangent screwmotions, &c., in case. [51] Improved Varley Stand, with rackwork movements, adapted for a telescope of 5 or 6 ft. focus: fixed upon a circular turn-table, so as to be easily pointed in any direction. [16] Polar Axis of mahogany, 7 ft. long, adapted for a 4 ft. telescope, with 12 in. circles, reading to minutes. [56] Speculum Grinding Apparatus, capable of working a 7 ft. speculum: with tube and fittings for a 9 in. Newtonian. [57] Brass Orrery and Tellurium (one or both), designed by and formerly the property of the late Dr. Pearson, and purchased by the present owner at his sale of instruments in 1853. [59] Recreative Science: complete in numbers, half-price. [30]

FOR

OR SALE—an excellent REFLECTING TELESCOPE, focal length 7 ft., aperture 7 inches, mounted so far Equatorially that with a little care it may be turned on a star or planet in the day-time.-Four Eye-pieces.-Price £20 only (less than the cost of the stand), the proprietor having mounted a larger instrument. [11]F

INSTRUMENTS, &c. WANTED.

Equatorial Stand Wanted--adapted for a 5 ft. Refractor, with graduated circles; second-hand, at a moderate price. [35] Monthly Notices of the Royal Astronomical Society. The third volume wanted: a good price will be given. [26] Schröter's Selenotopographische Fragmente-a copy wanted, [ 49 ]

in two volumes.

QUERIES AND REPLIES.

A URSE MINORIS.-Has anyone noticed, during last winter and spring, the difficulty, indeed all but invisibility of this star, except by averted vision, even under the best circumstances, with the naked eye? I saw it very well with the equatorial, with incipient twilight repeatedly. It naturally struck me it could not have been always so, being a standard star of the Nautical Almanac. I do not find it in any list of variables.

T. W.

COMETARY ORBITS.-In answer to B. A. (June Register), Milnes' Prize Essay on Comets, published in 1828 (Black, Edinburgh; and Longman, London), gives an example of the computation of a parabolic orbit, after the manner of Olbers, also formulæ for the calculation of an elliptic orbit. This is the only volume I possess. Would not the information be gained in Gauss's Theoria Motus Corporum Celestium (there is an English translation), and the Astronomies of Delambre and others? I hope some one will indicate the work which contains the most recent and approved method of dealing with this subject. G. J. W.

ASTRONOMICAL REGISTER.

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