: 131'1 133'7 136'4 Query Which point or spot near the middle of the moon's disc is practically the best adapted for serving as a fundamental mark in selenographical investigations ? The best determined point on the moon's surface is the centre of the crater Moesting A (in lat. 3° 11' and long. 5° 13', or colong. 95° 13)', which has been used as the mark of reference in the Koenigsberg observations for the investigation of the moon's librations. Bessel selected this crater in preference to others, because, as he states (Astron. Nachrichten, vol. 16, p. 276), “it appears, even in full moon, very bright, and in sharply defined form, and also because it may, by means of its surroundings, be easily distinguished from other similar craters, so that the observer is not exposed to the risk of mistaking it." Bessel made his selection on March 31, 1839, two nights after full moon, and there is no question that for some days before and after full moon, when the crater is fully lighted up, it makes a very good mark. But it seems very questionable whether nearer the times of first and last quarter, when the interior of the crater is partly shaded, its centre can be correctly estimated without considerable difficulty. Will observers of the moon who have the opportunity please watch and sketch the appearance of this crater under its different illuminations? And will they please try to find a really better mark, if it exists? Maedler suggested (Astr. Nachr., vol. 15, p. 12) the crater Triesnecker B, but its variable appearance tells likewise against it. LUNAR OBJECTS SUITABLE FOR OBSERVATION IN AUGUST, 1872. BY W. R. BIRT, F.R.A.S., F.M.S. The lists for May and July, 1871, may be employed for the selection of objects suitable for observation in August, 1872. On p. 150 of the June number of the present volume, the value of supplement - on May 21, 1871, is given as 152° 21. On August 6, 1872, the value of supplement < O will be 151° 21. In vol. ix., pp. 172, 173, the values on July 20 and 31, 1871, respectively were 142° 24.8′ and 1° 32''7. In 1872, on August 13, supplement <= 1° 50'4. The two lists are therefore available from August 6 to 18 of the present year. Eighth Zone of objects from North to South. Palus Somnii, Guttemberg, Magelhaens, Colombo, Sautbech, Borda, Metius, Fabricius, Janssen,(a) Rosenberger. The eastern boundary of the preceding seven zones was printed in the last communication as 25° of west longitude. It should have been 45°, which would, according to the suggested admirable alteration, for some purposes be 45° from the western or preceding limb at mean libration. The present zone extends 5° further eastward, i.e., to 40° west longitude, or 50° from the preceding limb at mean libration. The objects will be coming into sunlight on the 7th astronomical reckoning, and may be looked for on the evening of the 8th, when the moon is about four days old. As the autumn approaches the early moon has decreasing altitudes in the western sky, but this disadvantage is compensated by the much greater facilities for observing the objects in the eighth zone under the setting sun during the first four days after full moon, and it is recommended that advantage be taken of the harvest and hunting moons for observing the objects in the eight zones. It is suggested that particular attention be given to GASSENDI under every illumination, several gentlemen have had it under observation for some months past, and additional observations will be valuable. (a) See list for September, 1871, vol. ix., p. 217. Mercury may be observed at the beginning of the month as an evening star, setting on the 1st about 48 minutes after the sun, the interval decreasing. Venus is still too close to the sun to be well observed. Saturn may be fairly observed till after midnight, setting at the beginning of the month two hours and a half after midnight, the interval decreasing at the end of the month to about half an hour. REVIEW. Essays on Astronomy. By Richard A. Proctor. Longmans, Green & Co., 1872. We are glad that Mr. Proctor has determined to publish in a collected form some, if not all, of the many articles and notices which have appeared from his clear and running pen in the various serials and reports of the societies. In the present volume he has gathered together a number of essays upon more strictly scientific subjects, and he promises a second volume of a somewhat lighter kind, and more closely associated with the subject of the plurality of worlds. There are in the present volume three interesting articles upon Sir John Herschel; others on the planets Mars and Saturn (beautifully illustrated); meteors; the zodiacal light; the Sun's corona; coloured suns; Sirius, &c. Some of the more abstruse subjects have been been put into the appendices, among which we may notice an able paper upon the transit of Venus in 1874. Mr. Proctor, in answer to those who profess to object to popular science, and who would imply that, because he has done so much to make science popular, he necessarily has written in a superficial way, says that he has never written anything in the popular serials upon any subject that he had not previously treated more solidly. This is always borne out by the dates of the various essays. We believe that he has done much to incite an interest for these subjects among those, who under ordinary circumstances, would not have dared to encounter the difficulties |