where he says the willow-leaves are given up, and that the objects seen are not clouds, Mr. L. hoped to show that if not clouds they were very like them. Mr. Stone: As to seeing faint points of light, I may mention that I draw stars three times as large as Mr. Carpenter, while he discerns faint points rather better than I do. Mr. Huggins: I think both results of observation are right. I have seen objects sharply defined, and not far from round generally. On one or two occasions there have been appearances closely resembling the drawings of De la Rue and Nasmyth; but these have been round spots, where local action seems to take place and elongate the objects, so that the drawings represent faithfully what may have been seen. On a New Arrangement of Two Prisms for a Solar Micrometer, by Mr. Dawes. Sometimes a glass diagonal reflector and large aperture are useful, but in this case the direction of the rays is different, and causes confusion as to the sun's axis, which with micrometer measures is still more troublesome. By using two prisms this is corrected, and Mr. Cooke has made me such an arrangement. [The instrument was shown.] The mounting, however, is not exactly what I intended. It will be useful for measuring, but is not likely to improve definition. It is a curious thing, that on referring to the works of Barlow and Hutton, I find the use of a glass for reflecting the sun's rays in telescopes is due to Hooke, who described the application 200 years ago. Mr. Pritchard drew a diagram of the passage of the rays through the eye-piece, so as to procure direct vision. By the use of the diagonal glass reflector we can work with the whole of a large aperture. Sir J. Herschel suggested this in his Cape observations; but if parallel glass be used, the light is beaten backwards and forwards between the surfaces, and impairs definition. This is avoided by cutting off the back surface in a slant, and making a prism of the reflector. It is very curious that, without ever having seen Sir J. Herschel's book, Mr. Cooke has long been supplying a prism with his telescopes, and this was used by Piazzi Smyth on Teneriffe. Now, by the second prism we get direct vision, as well as getting rid of heat and light. However, it seems as if there is nothing new under the sun, and that the diagonal reflector is 200 years old. Mr. Simms states that Troughton did the same thing, with a difference—he used a metallic reflector, which absorbed some light, but not the heat. A paper by a Professor at Utrecht, On Comets, was announced. By discussing those since 1844, he arrived at the conclusion that each star had its own set of comets, which, after perihelion, darted off in hyperbolic orbits, and, coming within the range of other stars, passed round them,' and then travelled away in fresh paths. CORRESPONDENCE. N.B. We do not hold ourselves answerable for any opinions expressed by our correspondents. THE SOUTHERN COMET-LARGE METEOR. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-As I find no elements of the Southern Comet in the number for May of the Astronomical Register, the following statement of them, contained in a letter to Sir John Herschel, from Mr. Hind, will perhaps meet the wishes expressed by your correspondent S.B.K. :— "Elements of the Southern Comet, from Mr. Ellery's observations, at Melbourne, on January 20, 22, and 24. The Southern Comet is therefore distinct from the Great Southern Comet of the year 1843, a similar list of whose elements would be A large meteor occurred on the 10th of February last, at Bangalore, between Madras and Bombay, in Southern India, where it was supposed to predict the death of a native rajah! Indeed, that of the Rajah of Mysore shortly afterwards took place, in which province Bangalore, next to Mysore, is the principal town. The date is one of the three dates named beforehand for February, as likely to be distinguished by the occurrence of large meteors: vide the Astronomical Register for January. The meteor appeared larger than the moon, which at that time was full, and it left a trace for five minutes. It exploded at Salem, in the Carnatic, with a noise equal to a hundred cannons. I am, Sir, yours obediently, Collingwood, Hawkhurst : 02 CYGNI. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir, I have devoted several evenings lately to the measurement of the two companions of O2 Cygni, called C and D in the celestial cycle. The position and distance deduced by me from 8 or 10 observations, assign to C an angle of 174° 17', and a distance of 106" 66, thus coinciding remarkably with the measures of Piazzi, South, Struve, and Smyth, and showing that no physical connection exists between these two stars. on. But with respect to D, a discordance is apparent, which cannot be accounted for on the supposition that a periodic revolution is going In 1863 I ascertained its angle of position to be 323° 14'; in April 1865, 323° 29'; and in the present month, 323° 11'; giving a mean of 323° 18'. Piazzi in 1800 calls the position 324° 30', which is not very different. But Struve and Smyth ascribe to D the angles 333° 42′ and 333° 48′ respectively the difference here becomes too great to be overlooked. I would gladly defer to these experienced observers; but perhaps some of your readers could put the matter beyond doubt, by giving us the result of other measures. I may add, that all are nearly in accord as to the distance of D. I remain, Sir, obediently yours, GEORGE WILLIAMS. Prince's Park, Liverpool: May 3, 1865. GAMMA VIRGINIS-BIELA'S COMET TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-Having on four evenings last month got 19 measures of Y Virginis, giving for a mean -I should be glad to hear from any of your correspondents the true position and distance, as also those of & Bootis and 44 Bootis. The telescope has a 43 object-glass, by Cooke. Also, I should be glad if any of your readers could tell me, through the medium of the Register, the name and particulars of any book from which I could get a start at cometary orbits. In the Intellectual Observer for February is an announcement for the autumn of this year of Biela's Comet. Can anyone please inform me how small a telescope I should be likely to see it with? York, 10-5-65. Yours truly, B. A. OCCULTATION BY THE MOON. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-Perhaps some of your readers can tell me what body was occulted by the moon on the evening of April 29th, at 9h. 35m. local mean time. This observation was made accidentally with a 23-inch Dollond. The star seemed to have a disc, and to be much fainter than I have observed a star of the 8th magnitude under similar circumstances. With the help of Dietrichsen's ephemeris, I estimated the position of the star to be These co-ordinates are but approximate, as the star was not seen to come up sharply scintillating to the moon's limb, and the watch error was uncertain. But if all the planetoids are tabulated, my rough estimates might serve to identify it. I can scarcely hope that it is among the unnamed wanderers of our system. Portadown, Ireland: I am, &c., THOMAS BUCHANAN. SPOTS ON THE SUN. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-In reply to the query of your correspondent D. A. Freeman, in your number for May, I may inform him that I observed the sun on the 22nd March, when its surface appeared to be entirely free from spots. The instrument used was a 41 Achromatic, by Cooke & Sons. Near Garstang, Lancashire: I am, respectfully, C. W. THE SUN'S DIAMETER. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-Mr. A. S. Herschel remarks, in his letter (inserted in the January Number), that "it is more difficult to detect a disproportion in the different solar diameters, arising from the effects of refraction, at moderate altitudes, than to observe the alternate enlargement and contraction of the sun's disc in periphery and area," &c. This difficulty is confined to high latitudes, in an opaque and changeable atmosphere, and where the sun's apparent daily path can only be seen obliquely to the horizon, as in England. Within the tropics, where the atmosphere is, generally speaking, serene and clear for weeks together, there is no more difficulty in measuring the variable diameter of the sun from east to west than from north to south in the meridian, provided the sun's declination corresponds with the latitude of observation. I obtained the following measurements on the flank of the Central Andes, in latitude 5° 10" North; elevation above the level of the sea 3,000 feet, mean temperature 73° Fahr., mean height of the barometer 27 300: It is well known to those who are accustomed to take lunar distances, that the more a couple of stars are elevated from the horizon towards the zenith, the less will be their apparent distance asunder, and vice versa. In like manner, two points marked on the limbs of the sun, diametrically opposite horizontally, vary in distance, like the stars, according to the altitude. This is evident from the consideration that the altitude of any given celestial point is an arc of an azimuth circle intercepted between the object and the horizon; and as all azimuth circles incline gradually to each other from the horizon to the zenith, it is plain that the more two stars or two points are raised by refraction, the less becomes the apparent distance. I have never found the measurements of celestial bodies (such as the sun, moon, and planets) by means of wires in the telescopes in connection with the time of transit, or by a micrometer, as accurate and satisfactory as those obtained by a first-class sextant with double images, and the contact of the two limbs delicately adjusted in the centre of the telescope. The positive and negative readings correct the error of the instrument. This may vary in amount several seconds in the course of an hour, should the instrument be exposed to the rays of the sun at high latitudes. I remain, Sir, yours very faithfully, 15, Clarendon Gardens, Maida Hill, W.: 2nd March, 1865. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-With regard, once more, to the question of the apparent solar diameters, at various seasons and under different circumstances, nothing, truly, is more palpable than that departure from the figure of a perfect sphere which the sun's disc undergoes, as Mr. Hickson remarks, when very near to the horizon-a fact often observed, and to which I called attention in my tables of solar diameters at pp. 211 and 212, in your impression for September 1864; wherein, for instance, I showed that on July 6, 1864, at 3h. 58m. A.M. (or about five minutes after sunrise), the excess of the horizontal over the vertical diameter amounted to 2' 27′′, being a difference of very nearly 1-13th part; whilst, again, on July 14 of the same year, at 7:58 p.m. (or about twelve minutes before sunset), the excess amounted to no less than |
