Abstract
LONDON
Royal Society, Feb. 17. —The following papers were read: “Account of the Great Melbourne Telescope from April 1868, to its commencement of operations in Australia in 1869.” liy Albert le Sueur. The author stated that the building in which the telescope is placed is rectangular, 80 feet long merirlionally by 25 wide, with walls 11 feet high. Of the meridional length, the telescope-room occupies the north 40 feet; the next 12 feet are appropriated to the polishing machine, crane, and engine; the remaining 28 feet are divid ed into two rooms, one of which is at present used as an office, the other, 25 by 14, is intended for a laboratory. The moveable roof is 40 feet long, and runs on rails laid the whole length of the walls; the telescope room may therefore be completely covered in, and as completely uncovered when required, the roof in the latter case resting on the south building, which on that account has a very low permanent roof. The telescope, when housed, lies meridionally on the east side of the pier, and nearly in a horizontal direction, provision having been made to prevent the tube being lowered beyond a certain small inclination. Some trouble was experienced in removing the varnish from the specula, and they would require repolishing. Of work done, the author could not yet speak with any satisfaction since it became at all practicable to use the telescope; the history which he had to relate was a long chapter of weary heart-breaking watchings, with an occasional half hour's work. η Argus was the first object observed for purpose of delineation; after the first night's work little (and that by snatches) was done towards it; a new inroad of workmen and a long course of extremely unfavourable weather having carried the nebula out of convenient reach. The search, which was reluctantly given up, will, however, be again soon resumed. The horseshoe nebula is a grand object, conspicuous and with shape even in the finder. It appears, however, to present no marked difference (with perhaps one exception) which may not be accounted for by the difference of aperture used. This exception is the presence of a small but conspicuous double star at the s p angle of the knot which lies between the ɛ and the bright streak; the experiment has not been tried of cutting down the aperture to approximate to an 18-inch Herschelian, but the intrinsic brightness of the principal star, and the presence in the C G H of stars not more bright (No. 3 of Herschel's catalogue is certainly less bright) go far to show, without this experiment, that the star did not exist as such with its present brilliancy at the time of the C G H and P T 33 observations. The important position of the star, and the careful scrutiny which the knot and its neighbourhood must have repeatedly undergone, forbid the assumption that it was simply overlooked by SirJohn Herschel. The star β is conspicuously and beautifully double, the companion of considerable brilliancy, about 15 mag.; with its present brilliancy and elongation, the author thinks, it should be within reach of an 18-inch. The appearance of the knot is sparkling, though no discrete stars can be seen, except perhaps a second faint one, which is suspected at the s f angle; part of the streak near to the knot is also sparkling, but not in so marked a manner; the other portions appear of the ordinary milky nebulosity. The fainter nebulosity (S) of the bright streak pretty well marks out the borders of the almost vacuous lane which leads up to and past the knot; on receding from the lane it becomes very faint; nor is this faintness uniform, but the appearances are so fugitive that, after repeated and painful effort, they could not be caught. The borders, however, stretching to the stars are occasionally pretty well seen. On one or two occasions the author suspected the existence of a link between the nebulosity about the star No. 10 and the lower portion of the 8; this, however, requires verification. At the f end, the upper and¨ smaller semicircle is plainly marked, the lower and larger, very faintly; its exact figure is, therefore, uncertain. 3570 is a small but beautiful spiral. The two brighter knots are resolvable. Of work out of the regular course, amongst other things, Neptune has been observed on some five or six occasions for figure and a second satellite, with only negative results. In the absence of a photographic apparatus to be used at the uninterrupted focus of large mirror, attempts have been made to utilise the second or Cassegrain image; an average exposure of near ten minutes on an eight-day moon produced pictures which (by no means good) were of sufficient promise to make it worth while to resume the attempt under more favourable conditions. The time of exposure is somewhat surprising, and would seem to indicate a great loss of chemical rays by a second perpendicular reflexion; but perhaps the inactivity was mainly due to absorption at the surface of the large mirror, which was then very yellow. The spectroscope arrived some time ago, but has not been much used; it is thought that for star work of any value some modification will be required, principally the exchange of the present collimator for one of longer focal length; a greater dispersion, '. moreover, seems desirable. The spectroscope was mainly designed for nebula work, is handy and compact, and will be of much service. For spectroscopic work on objects having a sensible diameter, the great telescope itself labours under some disadvantages; the enormous focal length and consequent magnification of the image is a serious inconvenience in the case of faint objects, and may be only partially remedied by a suitable condenser. This magnifying of the image may, however, in some cases be advantageous, from the possibility thereby afforded of viewing small definite portions of moderately bright objects, though unfortunately that will be seldom. Of nebula?, Orion has been examined for purpose of practice; the three lines are plainly and conspicuously seen; the hydrogen line is comparatively much fainter than was anticipated, disappearing in the fainter portions of the nebula. 30 Dorads shows the nitrogen line with facility, the second line certainly, but not in all positions, and always with difficulty; the hydrogen line is suspected only.
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Societies and Academies . Nature 1, 443–446 (1870). https://doi.org/10.1038/001443a0
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DOI: https://doi.org/10.1038/001443a0