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The photographic news
- Bandzählung
- 35.1891
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- 1891
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- Bandzählung
- No. 1711, June 19, 1891
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The photographic news
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454 THE PHOTOGRAPHIC NEWS. [June 19, 1891. out details of plate-holders, rseau-frame, and other accessories after the instrument was set up. Unfortunately, when it was otherwise ready for use, the ratchet to the weight barrel of the driving clock—which was of the silent form—gave way on October 27th, 1890, letting the heavy weight fall. The barrel was sent to Sir H. Grubb, who applied an ordinary ratchet to it, with a new steel pinion, and returned it on November 24th, 1890. The instrument has since worked very satisfactorily, and is admirably adapted to its purpose, the electrically con trolled clockwork in particular being very efficient. Work with the 13-inch photographic refractor was seriously delayed by this accident to the driving clock, and later by the illness of Mr. Criswick ; but 81 stellar photographs have been taken, all of which must be regarded as more or less experi mental. Ferrous oxalate development was used throughout, and all the plates were photographically impressed with the rseau kindly supplied by Prof. Vogel. The exposures have varied from a few seconds to about an hour ; and trails have been taken both on the equator and near the pole to test the adjustment for orientation. Several different kinds of plates have been used, including Cramer, Seed, Paget, Star, Mawson and Swan, and Ilford, and, on the whole, the choice seems to lie between the Star and the Ilford plates. Some trial photographs of Polaris have been taken with the Dallmeyer 4-inch photo-heliograph object glass, which it is proposed to use as an auxiliary telescope to test the quality of the night by short exposures on Polaris during the exposures for the chart plates. Speotroscopic and Photographic Observations.—For deter mination of motions of approach or recession of stars, 286 measures have been made of the displacement of the F line in the spectra of 31 stars, and 14 of the b line in the spectra of 6 stars, besides comparisons with the spectra of Mars, the moon, the sun, or the sky as a check on the general accuracy of the results. The series of observations with the 124-inch refractor is now practically completed, and the results are under discussion. An examination of those for the 21 stars most frequently observed shows that there is a systematic error depending on the hour angle, thus necessitating a correction for the position of the spectroscope at the observation. In the year ending May 10th, 1891, photographs of the sun have been taken at Greenwich on 224 days, and, of these, 483 have been selected for preservation, besides 18 photographs with double images of the sun for determination of zero of position. For the year 1890, Greenwich photographs have been measured on 209 days, and photographs from India and Mauritius filling up the gaps in the series on 152 days, making a total of 361 out of 365 on which photographs have been measured in this year. The sun has been free from spots on 175 days in the year 1890, as compared with 211 days in 1889. There were only three spotless periods of more than 14 days in 1890, viz., February 2nd to 27th, March 24th to April 9th, and June 11 th to July 3rd, while in 1889 there were nine such periods. The mean daily spotted area has increased from 78-millionths of the sun’s visible hemisphere in 1889 to 100 in 1890. The measures of the photographs and the reductions of areas and positions of spots and facul are complete to the end of 1890. Photographs from India and Mauritius have been received from the Solar Physics Committee as far as February 4 th and January 23rd, 1891, respectively. As regards the further discussion of the results of former years, 46 Melbourne photographs, available for filling up gaps in the series in the year 1877, have been measured, and these, together with those for the years 1875 and 1876 referred to in the last report, have been completely reduced, the orientation of the wires having been inferred by comparison with measures of Greenwich and Harvard College photographs on neighbouring days, as no satisfactory details of this adjustment could be furnished from Melbourne. The copy for press, both of the daily results and the ledgers of sun-spots, is completed for these years. Ledgers of the positions and areas of spots for the years 1882 and 1883 are completed and ready for press, and those for 1884 and 1885 are being formed. When this is done, the reductions for the whole series of years from 1875 to the present time will be complete, those of the Indian photographs for the years 1879 to 1881 having been completed at South Kensington under the supervision of the Solar Physics Committee. Magnetic Observations.—The photographic record of the three magnetic elements, and the supplementary eye observations, have been continued as before. The temperature of the base- ment in which the photographic instruments are installed has been maintained at about 67° throughout the year, except in December and part of January, when the gas supply again became deficient, and the ground in the park was again opened to clean the pipes, which were found to be so much corroded that it will be necessary to renew them. They have been in use as gas-pipes for forty years, and had previously served as water-pipes before the existing water main was laid down. The magnetic reductions are completed to the following stages :—The eye observations of the upper declination magnet, and of the horizontal and vertical force magnets, are completely reduced to the end of 1890. The time-scales for declination, horizontal force, and vertical force are complete to the end of 1890, and the base line values, deduced from eye observations, are entered on the photographic sheets for declination and for horizontal and vertical force. The hourly ordinates of the photographic curves are read out to the end of 1890 for all three elements, and the daily and hourly means are all taken ; the time scales for earth currents are laid down. The dip observations are completely reduced to the present time, and the deflexion observations for absolute measure of horizontal force to the end of 1890. The temperature of the magnet basement at every hour has been read off from the sheets of the Richard thermograph to the end of 1890, and the daily and hourly means have been taken. The meteorological reductions are in the following state :— The observations of barometer, thermometers, anemometers, rain gauges, and sunshine recorder (corrected, where necessary, for instrumental error) are reduced up to the present time. On the photographic sheets all the time-scales are laid down, and the hourly ordinates are read out for the dry and wet bulb thermometers and electrometer to the end of 1890, and some work has been done in taking means. General Remarks.—The preparatory work for the photo graphic map of the heavens has occupied a good deal of attention during the past year, a number of new questions being raised in this application of photography to systematic astronomical work which have necessarily required careful consideration on the part of the chief assistant and myself. Under these circumstances the want of increased supervising power for the Observatory has been severely felt, and this want has not been in any way met by the appointment, after a long delay, of an additional second-class assistant. The recent meeting at Paris of the International Committee for the photographic map, in which I took part, settled the bases of the work in a general way ; but for working out the details, both practical and theoretical, much remains to be done, and, under the existing conditions of the Observatory staff, it is difficult for the chief assistant and myself to supervise this adequately, and to deal effectually with the important points of principle involved in the discussion of the excellent photographs which have been obtained by Mr. Criswick and his assistants. Halifax CAMERA Club.—At a meeting held on Monday last, it was unanimously resolved to form a photographic club for Halifax and neighbourhood, and to make an effort to obtain suitable premises and have them thoroughly fitted up as a first- rate studio, embracing not only studio proper, dark room, enlarging room, and dressing room, but also a large room for meetings and lantern entertainments, and a reading room provided with the current photographic literature. During the evening no less than £20 was promised towards a furnishing fund in addition to subscriptions. The annual subscription was fixed at 10s., and the Club is to be open to both sexes, and to professionals and amateurs. At the close of the meeting the names of forty-two persons were taken down as members. The honorary secretary, pro. tern., is Mr. E. Finlinson, Union Bank, Halifax, from whom full information may be obtained.
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