of the proposed map-75 inches in diameter-a skeleton map of that size being exhibited. Mr. Birt had been very assiduous during the year, having been engaged 125 nights and mornings in making observations, of which 1,812 were micrometrical. The correspondence on many topics connected with this work had been extensive; the Rev. W. R. Dawes, the Rev. T. W. Webb, D. A. Freeman, Esq., George Knott, Esq., and other gentlemen, had communicated observations of an interesting and important character. Taking into consideration the three portions of the work that had been entirely performed by Mr. Birt-observation, computation, and correspondence the Committee thought it desirable that a clerk should be placed at his disposal, and recommended to the Section that an augmented grant from the funds should be applied for to meet this object. Mr. Birt, as Secretary to the Committee, then presented his Report, and described by the aid of the skeleton map already mentionedhow, for the purposes of compiling a catalogue of lunar objects, and the construction of a map of the moon's visible surface, that surface had been divided into four quadrants, each being subdivided into sixteen grand divisions, which are distinguished by the first sixteen capital letters of the Roman alphabet. These sixteen divisions are again divided into smaller spaces of five degrees of latitude and longitude, which are further distinguished by the small Greek letters. By means of this arrangement, any particular object that has been the subject of observation may be so designated that ever afterwards it can readily be referred to. In speaking of the progress made with the catalogue, Mr. Birt said that, at the meeting of the Association at Bath, he stated, in a paper published in the Transactions of the Sections, that he had entered 386 lunar objects in certain preliminary Forms, which have been extended in Form No. 3. During the past year, the number of objects catalogued from personal observation is 319, making together a total of 705 lunar objects symbolised and entered. In Form No. 3, 379 are entered on 82 sheets, 326 on 49 sheets of the preliminary Forms still remaining for transfer into the Association Forms. Mr. Birt described some interesting portions of the moon's surface which had passed under his notice during the year. They may form the subjects of special communications to the Register. A few drawings of lunar craters were exhibited; Mr. Birt received them from the observatory of Lord Rosse on the day previous to reading the Reports. At the conclusion of the reading of the Reports, the President of the Association, Professor Phillips, congratulated the Association on the progress which is being made in this special branch of study. The few drawings exhibited, he presumed, were specimens of the large contribution which Lord Rosse is expected to make on the subject. With the telescopes now made, many small objects could be seen very distinctly, and even Birmingham would be a considerable luminous spot were it upon the surface of the moon. The Professor pointed out that there is a large field for special discovery on the moon's surface, particularly on the large grey tracts, and it would be well for observers to scrutinise these tracts with the utmost exactness, and watch the undulations that are visible upon them. The systems of rilles are also most interesting. With regard to minute objects, Professor Phillips referred to the ring mountain Gassendi, and instanced the central mountain, which is generally drawn with one peak; he said there were more. Two appeared in the drawing of Lord Rosse's artist, and Mr. Birt mentioned that five had been quoted. Mr. W. R. Grove followed with some important and very appropriate remarks on the relative ages of lunar formations: for example, we know that a small crater opened within a larger crater must be the most recent, and he gave an instance of four craters, three one within another, the three occurring in a larger crater. In the same way an opening perforating a ring is more recent than the ring itself. careful examination of portions of the moon's surface of this character would amply repay the observer for his attention. A We hardly need say that observations of the nature pointed out by Professor Phillips and Mr. Grove will be very acceptable to the Committee, especially as cooperation is much needed. All communications should be addressed to the Secretary, Mr. W. R. Birt, at his residence, No. 42 Sewardstone Road West, Victoria Park, London, N.E. DEATH OF SIR W. R. HAMILTON.-Sir William Hamilton, Professor of Astronomy in the University of Dublin, and Astronomer Royal for Ireland, died last month. He was appointed Astronomer for Ireland in 1827. He was one of the first mathematicians of the day, and was the author of several essays. He did little, however, for the progress of our science, and we hope that his successor, whoever he may be, will be a more practical and working man. AGE OF THE PYRAMIDS OF EGYPT.-Mahmud Bey, Astronomer to the Viceroy of Egypt, has published an interesting treatise, with the view of proving their dates from their connexion with Sirius, the Dogstar. The late Viceroy, Said Pasha, ordered him to work out this problem. He found the exact measurement of the largest to be 231 mètres at the base, and 146·40 from the ground to the apex. Hence follows that the sides are at an angle of 51 deg. 45 sec. Mahmud Pasha found that the angles of the other three pyramids, near Memphis, were on an average inclination of 52 deg. The fact that the sides of these monuments are placed exactly true to the four quarters of the globe, seemed to point to some connexion with the stars, and Mahmud Bey found Sirius sends his rays nearly vertically upon the south side, when passing the meridian of Ghizeh. He then found, on calculating back, the exact positions the star occupied in past centuries, that the rays of Sirius were exactly vertical to the south side of the Great Pyramid. 3300 B.C., Sirius was dedicated to the god Sothis, or Toth Anubis, and hence the astronomer deduces, that the Pyramids were built about 3300 B.C.-a date nearly coinciding with Bunsen's calculation, who fixes the reign of Cheops at 34 centuries before Christ.-Builder. CORRESPONDENCE. N.B.-We do not hold ourselves answerable for any opinions expressed by our correspondents. BINARY STARS. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-In the September number of the Register, a correspondent suggests the desirability of a periodical statement of the co-ordinates of the more interesting binary star systems. Should such a plan find general favour, I can only say that I shall be most happy to communicate such observations as I may possess, though I fear they will never be very numerous. In the meantime I have the pleasure of handing you the results of some recent double-star measures, taken with my 7-inch Alvan Clark refractor, and a filar micrometer by Dollond. With three exceptions, the observations were all taken in the present year. I do not know that the annexed list needs any explanation, with the exception that the column headed n contains the number of nights on which the corresponding observations were made. In the cases in which the star was observed on one night only, the measures are, of course, open to some uncertainty. I insert them, not from their value as measures, but because they may be of interest to some of your readers : Star's Name : 7 Cassiopea 36 Andromeda a Piscium 333 1865.69 3 1865.69 3 1865'47 52 Arietis n Cassiopea. This star has undergone considerable changes both in P. and D. since the earlier epochs. 36 Andromeda. Now an easy object: widely separated. a Piscium. The angle of position and the distance appear to be decreasing. I have had some trouble with the colours of this pair. Are they variable? Andromeda B. C. An elegant test. The angle appears to be slowly decreasing. I doubt whether I have really seen them fairly separated with my 7-inch object-glass. An 8-inch aperture should show a real separation. The distance was measured on three nights only. 52 Arietis. This pair appears to have changed but slightly since the earlier epochs. It is clearly divided in my instrument. C. is, to my eye, considerably brighter than the more distant comes D. η Orionis. One of the Rev. W. R. Dawes's discoveries. Unfortunately, it is not very favourably situated for observation in these latitudes. The distance depends on one set only. 42 Orionis. So far as I am aware, this pair was discovered by myself in February 1863. It is an elegant test object for an instrument of moderate power. Castor. My measures of this object differ more than I should have expected from those of Mr. Dawes (see Register for September). The difference in the angle is probably due to the oblique position of the pair. The measures were, to the senses, very satisfactory. μ Bootis. A neat test. The close pair not separated in my instrument. The distance only estimated. π Aquile. But little change, if any, appears to have taken place in this pair. The Rev. T. W. Webb recently pointed out to me a minute comes at a moderate distance in the n. p. quadrant. A line from B. over A. will pass nearly over it. Its colour appears to me to be a pale blue. I have not yet succeeded in measuring it. 3062. An elegant binary star s. p. B Cassiopeæ, discovered by Sir W. Herschel. It has widened considerably since it was measured at Dorpat. It is prettily grouped with the pair Σ 3057 (P. = 298°.55. D. 3'574". Ep. 1863 52), forming with it a double-double star, with three small stars between the sets. = I cannot bring these remarks to a conclusion, relating as they do to a branch of observational astronomy with which his name will ever be closely associated, without briefly adverting to the heavy loss we have recently sustained in the death of Admiral Smyth. An ardent and successful cultivator of science himself, he was, at the same time, preeminently a large-hearted man, ever ready (to use his own words) to cast out a tow-rope," and to "second the efforts of all zealous amatores scientia" with a hearty kindness which could not fail to win the respect and esteem of all who had the good fortune to come in contact with him. 66 I am, Sir, yours faithfully, Woodcroft Observatory, Cuckfield : GEORGE KNOTT. STAR MAGNITUDES AND LIMITING APERTURES. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-Having often been greatly assisted by the notes on different subjects sent to the Register, I send you the following, in the hope of their proving useful to some of your readers. 1. If unity represent the amount of light received from a star of the first magnitude, the series representing the same for stars of the 2nd, 3rd, 4th, 5th, &c. mags. will be where is the light-ratio, necessarily a fraction. Therefore, generally, if L be the amount of light received from a star of the mth magnitude as a fraction of that received from a star of the first magnitude, L = pm-1 or m=1+ log. L log.p .Eq. (1). 2. What numerical magnitude would result from the combination (as a double star, for instance) of two given magnitudes m and n? Let be the required mag., then μ -1 • . * L + L1 = μ“ −1 = cm −1 + pr-1...... Eq. (2). Example. Let the stars be of the 3rd and 5th mags., and assume the value assigned by Mr. Pogson. Here m3, n = 5, P = I 2'512 The combination of two stars of the 3rd mag. would, therefore, be to a star of the 2.2474 mag., and so for all others using the light 2'512 4. Given the limiting aperture a of an mth magnitude star to find that 0 of an nth. Since the amount of light passing through an objective is directly proportional to the area of that objective, it follows that the light received from any star varies inversely as the square of its limiting aperture: pm-1 02 |
