# A M W Downing's early publications

A M W Downing began publishing in 1877 and by the following year had around a dozen notes and papers in print. We give some extracts from a few of these below.

1. A Determination of the Semi-diameter of Venus at the mean distance of the Sun from the Earth.

Author: A W Downing, B.A.

Reference: Monthly Notices of the Royal Astronomical Society 37 (7) (1877), 398-399.

Date: 9 May 1877.

Extract: In this investigation I have made use of the results of the Washington Transit Circle Observations during the years 1866-1872 inclusive, the Transit Circle having been brought into use in 1866, and the results of 1872 being the most recent to which I have access. During this interval the value of the semi-diameter of Venus at the mean distance of the Sun from the Earth, given in the American Ephemeris, and with which the Washington Observations have been compared, was 8''.546. Let the true semi-diameter = $8''.546 (1 + y)$, so that $y$ = coefficient of variable part of correction depending on the planet's distance; and let $x$ = constant part of correction arising from irradiation &c.; we have then a series of equations ...

Using all the observations of vertical diameter of Venus made during the above-mentioned years, I have formed 167 equations in this manner; solving these by the method of least squares, I obtain ...

2. Title: The Proper Motions of certain Stars in the Greenwich Seven-Year Catalogue for 1864.

Author: A W Downing, B.A.

Reference: Monthly Notices of the Royal Astronomical Society 38 (9) (1878), 514-524.

Extract: Having occasion lately to refer to the proper motions of stars in the first four hours of right ascension, I was surprised to find that there were still so many of the stars observed by Bradley whose proper motions have not been determined by comparison with accurate modern places; so that astronomers still use, in many cases, the untrustworthy proper motions of the British Association Catalogue.

The present paper is an attempt to partially supply, for stars in the first four hours of right ascension, this deficiency in our knowledge of accurate proper motions. It contains the proper motions of the stars, within the above-mentioned limits of right ascension, which are common to Bradley's Catalogue in Bessel's Fundamenta Astronomiae and the Greenwich Seven-Year Catalogue for 1864, the quantities of proper motion being deduced from a comparison of the places given in these catalogues.

3. Title: On the Probable Errors of Transits of the First and Second Limbs of the Sun, observed by the Chronographic Method.

Author: A W Downing, B.A.

Reference: Monthly Notices of the Royal Astronomical Society 38 (3) (1878), 102-104.

Extract: It has always appeared to me, and I believe the impression prevails amongst most persons who are in the habit of constantly observing transits of the Sun, that the transit of the first limb is a more difficult observation than that of the second. This difficulty is occasioned, no doubt, by the fact, that in the case of the first limb the wires of the transit instrument are rendered faint by the glare of the advancing limb, whilst in the case of the second limb the appear as dark lines projected on the bright disk of the Sun as a background, and can be watched with ease during the transit of the limb. It occurred to me then, bearing this circumstance in mind, that it would be a matter of some interest to ascertain if the probable errors of transits of the Sun's first limb were sensibly greater than those of the second, and I accordingly entered upon the investigation, the results of which I have now the honour of laying before the Society. The materials used in the computation were the observations of the Sun made at Greenwich with the transit-circle from 1874, July, to the end of 1875, 100 complete transits having been observed during that time, and the mode of reduction being as follows : The time of transit over each separate wire has been reduced to the central wire by applying to the recorded time the adopted equatorial interval between the wire and the central wire, corrected for Sun's declination and increase of right ascension in the interval, and thus for each complete transit we have nine "central wires." I then take the mean of these, and find the difference of each from the mean. This being done for each complete observation, we have a number of "apparent errors," from which the probable error is found by the usual formula.

4. Title: The Proper Motions of the Edinburgh Star Catalogue.

Author: A W Downing.

Reference: Astronomical register 16 (1878), 129-130.

Extract: In Vol. XIV of the Edinburgh Astronomical Observations, 1870-1877, Prof Piazzi Smyth has attempted to correct the proper motions of the British Association Catalogue by observations made at Edinburgh and elsewhere, from 1830 to 1870. Prof Smyth seems to be possessed of the strange idea that the British Association Catalogue is still considered a high authority, both for position and proper motions, and does not appear to be aware of the fact that it is, and has been for some 10 years past, acknowledged (I was going to say universally) that one of the most pressing wants in the department of sidereal astronomy is a new general catalogue of the character, as regards extent, of that published by the British Association, which does not worthily represent the accuracy of modern observational astronomy; and in no respect is it more defective than in its proper motions, which are determined from too short intervals, as well as, in many cases, from not very accurate places. It is evident that Professor Smyth's proper motions labour under the former of these defects which, even if the observations were of an irreproachable character, would be detrimental to their accuracy; but when in addition we take into consideration the "swervings" of the Edinburgh transit instrument, it is impossible to regard them with any degree of confidence.

I think there can be no doubt that the best determinations of proper motions that we have as yet are those given by Mr Stone in the 33rd Vol. of the Memoirs of the Royal Astronomical Society. These proper motions are derived from a comparison of the observations of Bradley, vir incomparabilis, as given in Bessel's Fundamenta Astronomiae, with the Greenwich Seven-Year Catalogue for 1860. The epoch to which the observations of Bradley are reduced being 1755, this gives the long interval of 105 years for the determination of the proper' motions, and this, combined with the great reputation of Bradley as an observer, makes this memoir the most valuable contribution to our knowledge of this branch of astronomy that has yet appeared.
...

If these are fair samples of Professor Smyth's work it appears that much reliance cannot be placed on it, and that he has done but little even towards improving the proper motions of the British Association Catalogue.

5. Title: The Pulkowa double star observations (part 1).

Author: A W Downing.

Reference: The Observatory 2 (1878), 174-183.

Extract: One of the most interesting and important works in the department of sidereal astronomy that has appeared during the present year is undoubtedly Volume ix, of the 'Observations de Poulkova,' recently published by M Otto Struve, the able and energetic Director of the Imperial Observatory at Pulkowa. This volume contains the micrometrical measures of double stars made at Pulkowa from 1839 to 1875; and as, in addition to the observations themselves, the Introduction contains some curious and important researches on the subject of double-star observations, I have, at the suggestion of the Astronomer Royal, drawn up an account of the book, which will perhaps interest the readers of 'The Observatory.'

Since the foundation of the Imperial Observatory in 1839 the great telescope has been principally employed to study the relative motions of stellar systems, and though occasionally interrupted by other researches, the work has been persevered in up to the present time. Thus a long series of observations has been obtained which, being made by one person and always in the same manner, has the advantage of furnishing data of strictly the same character throughout, and in which the personal errors have only changed with the advancing years and more mature experience of the observer. The task which M Struve has set himself, and for the accomplishment of which he has laboured for so many years, is to furnish data as exact as possible for the study of the laws which regulate the relative motions in double and multiple systems of stars. The progress of science and the extension of our knowledge concerning binary systems have from time to time altered the character and direction of the work; and this is also the cause of the long delay in publication, as M Struve was unwilling to publish his observations till he had accomplished his task, at all events within certain limits.

Last Updated June 2021