The declination-circle is two feet in diameter, and reads by four verniers to four seconds in arc. The object-glass has fifteen inches clear aperture, and twenty-two feet eight inches focus. It is furnished with a filar-position micrometer, and four annular micrometers. There are eighteen eye-pieces, the highest power being estimated by the maker at two thousand. After adjusting and securing the various parts, the whole was found to move freely and steadily under clock-work, it being well balanced in all its parts, and the friction greatly reduced, by a judicious arrangement of counterpoises and friction-wheels. The instrument is protected from the weather by a dome of thirty feet interior diameter. It moves freely on eight cannon-balls, and is secured from displacement by storms, by eight iron braces, which are secured to the walls of the building, and present friction-wheels to the opposite sides of the interior of the dome. The opening is five feet wide; the shutters are opened and closed by means of endless chains, working in teethed pulleys turned by a crank. I omit the details of mounting the telescope, as they are of little general interest, and will be given in the report to the Visiting Committee on the Observatory, when I hope to be enabled to add to them an account of the new transitcircle, which Mr. Simms has nearly completed. η "In regard to the ultimate capabilities of our telescope, we cannot be expected, from so short a trial, to have formed any very decisive opinion. It has, however, even under the disadvantage of a bad state of the atmosphere, exceeded our expectations. We have had the best opportunities of making observations during the early morning hours. "Of the close double stars, our attention was first directed to Coronæ. The components appeared round, small, and well separated. The difficult double star y Coronæ, which Captain Smyth ranks in his Cycle' as the Præses of Struve's vicinissima,' was well separated, a dark space appearing between the principal star and its satellite. On the morning of the 20th July, the companion of y Andromeda was also well separated. The line micrometer gave a distance of three tenths of a second. I was surprised to find, on following this object into day-light, that our measures of distance could be taken after sunrise. I measured, alternately with my son, both in distance and position, while the sun was shining on the telescope, and we both thought that we saw them full as well, or rather better, after sunrise than before. This might be owing to a quieter state of the atmosphere consequent on a rise of the thermometer. On the evening of the 15th of July, the nebula No. 27 Messier, commonly known as the dumb-bell nebula, exhibited a multitude of points of light, with a few larger stars, which were probably accidental, or not belonging to it, scattered over its surface. Three observers were confident of the resolution of this nebula. It occupied considerably more space than the field of the telescope would take in, and the form by which it has hitherto been distinguished was entirely lost. There appear, however, to be two centres of condensation. "On the same evening, & Lyra was examined. It showed a small round disk; but the troubled state of the atmosphere rendered it unsteady. Thirty-five stars were counted in the same field with it. The ring nebula of Lyrae was beautifully shown. My friend, Hon. Wm. Mitchell, who was observing with us, was confident that he saw many stars within the compass of the ring. "The companion of Antares, discovered by Professor Mitchell of Cincinnati, was quite conspicuous, notwithstanding the tremulous state of the atmosphere at the low altitude of the star. The great nebula in Andromeda has a bright central point closely resembling a star. I do not recollect having seen any notice of this. "On examining the moon near the quadrature, the light is so exceedingly vivid, when the whole aperture of the object-glass is used with a power of 180, that it becomes painful to the eye. With higher powers, the mountains are brought out in bold relief, and the depths are opened. On the evening of the 20th, having a friend with me who takes a strong interest in these matters, we were examining the moon along the boundary of light and darkness, and saw what had every appearance of being the effect of atmospheric refraction. The deep black shadows of the rugged mountain-tops, stretching far across the plains until they were lost sight of in the unilluminated portion, enabled us by contrast to distinguish what seemed to be the first gray tint of dawn, and to trace the gradually increasing light to the full splendor of mid-day. 66 But I must recollect that you require of me only a brief account of our telescope. The objects revealed to us by this excellent instrument are so numerous and interesting, that it is difficult to know where to stop. "With the highest regard and respect, "I remain, dear Sir, yours sincerely, "To PRESIDENT EVERETT." In conclusion, Mr. Everett expressed the hope, that the members of the Academy might eventually witness such accessions to the astronomical science of the country, from the observations made by this admirable instrument, as would be considered by them a satisfactory equivalent for so large an appropriation of the Academy's funds. Two hundred and ninety-eighth Meeting. October 5, 1847. - MONTHLY MEETING. The PRESIDENT in the chair. The Corresponding Secretary presented a communication from Professor Henry, Secretary of the Smithsonian Institution, in reference to the organization of that institution; which, on motion of the Vice-President, was referred to a committee, consisting of Mr. Everett, Prof. Gray, Prof. Agassiz, Prof. Peirce, Prof. Longfellow, and Prof. Sparks. Mr. Bond communicated the following OBSERVATIONS ON THE PLANET Neptune, near ITS QUADRATURE. Made at Cambridge Observatory, Long. 4h. 44m. 32".. 1847. d. h. m. h. m. 8. App Declina | Obs.- Mean position of 38 No. of Aquarii, Jan. 1, 1847. Comp. h. m. 8. Aug. 18 11 13 22 05 41.75 -0.03-12 21 429+0.2 A. R. 22 02 26.57 4 Dec. -12°18′ 52.0 8 (6 20 10 11 22 05 29.36 -0.13-12 22 51 2-0.5 21 10 32 22 05 22.89 -0.25-12 23 26.5-0.7 38 Aquarii is No. 10 6 The columns headed "Observed - Ephemeris " contain a comparison with Mr. Adams's Ephemeris in the June number of the Notices of the London Astronomical Society. Mr. Bond also presented the subjoined OBSERVATIONS ON MAUVAIS'S COMET OF JULY 4TH, 1847. Cambridge Mean Solar Time. 1547. d. h. m. July 14 11 45 85 14 h. m. 8. s. h. m. 3. 16 20 Dec. N. 20 10 26 13 59 26.7 80 53 00 13 50 33.73 80 40 412 23 10 46 54 13 34 00.8 78 14 03 13 42 04.80 78 49 50.0 24 10 06 30 13 28 35.1 77 22 27 13 32 41.03 77 19 41.6 27 10 49 10 13 15 55.5 74 41 23 13 00 05.37 73 50 40 5 31 10 13 12 13 05 59.4 71 14 11 12 53 43 30 71 25 22.0 Aug. 3 10 32 48 13 01 15.4 68 43 14 12 26 55.11 70 37 55.7 10 9 11 00 12 55 48.2 63 12 43 13 00 19.88 62 51 47.9 Sept. 6 9 15 01 12 57 09.7 46 18 24 12 58 58 44 43 54 44.6 Oct. 11 7 07 30 13 09 46.2 32 35 45 13 11 02.75 32 26 23.1 July 14th. The comet was first seen at 11h 45m. P. M.; but after watching its position for some time, we could detect no indication of motion relatively to the neighbouring stars, so that it was not recognized as a comet until six days after. Its position, as given above, was taken from the circles of the five-foot equatorial. "July 20th. The comet was observed to-night with the five-foot equatorial, using the annular micrometer for the comparisons. It disappears sharply behind the ring, with almost as much certainty as a star; indicating a sudden condensation of light at the centre. This was afterwards confirmed, on examination with the great refractor recently mounted in the dome of the Observatory. With the full aperture of fifteen inches, a very minute stellar point is visible in the centre of the comet, with a sparkling light, easily distinguishable from the diffused nebulosity which surrounds it. "July 23d. The observations were made this evening with the great equatorial, by differentiating with the hour and declination circles. In high declinations this method allows the comparisons to be oftener repeated than is otherwise practicable. In declination the comparisons have a better mutual agreement than we have been able to obtain when using the annular micrometer. "July 24th. The comet does not sensibly increase in brightness. The stellar point is visible through strong moonlight. "Sept. 3d. The comet still shows a star-like nucleus. A faint tail is visible, of six or eight minutes in length. "October 11th. The differences of right ascension this evening are somewhat uncertain, the altitude being too low for accurate observations. "It seems necessary to remark, that the above places of the comet given by the great refractor of Cambridge University, having been obtained in every case from instrumental readings, and not from micrometric comparisons, are not determined with the full accuracy which the instrument is capable of affording. The mode of observation has been, to bring the object, by estimation, to the centre of the field of view, marking the time, and reading the circles for each in succession, and thence deriving their relative positions; a method which, however unpromising it may at first sight appear, affords, with practice, better differences of declination than are easily obtained, with smaller instruments, by the aid of the micrometer, and in high declinations is often decidedly preferable for right-ascension differences. The right ascensions and declinations of the comet were obtained by applying the observed differences to the place of the star of comparison referred to the mean equinox of Jan. 1st, 1847. Mr. Bond presented for publication a new series of moon culminations, observed at the Cambridge Observatory during the past and present year. MOON CULMINATIONS, Observed at Cambridge, Corrected for Instrumental Errors, Clock Error, and Rate. *B' is the initial of William C. Bond; B2, of G. P. Bond. |