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A.J. 591 of 55 pairs with the Kirkwood 12-inch; in M.N., 1908 January, of 86 pairs by Rev. T. E. Espin; and of 44 pairs at the Morrison Observatory. The measures of 1100 pairs made at the Observatory of Chevreuse by M. Farman in the years 1904-1906 are worth special notice. The measures were made with a 9-inch Cooke triplet.
The idea of M. Farman was to bring the Catalogues of Flammarion and Wilson-Gledhill up to date, and hence he supplements his measures by all those made of these particular stars since 1878, and it forms thus a fair-sized volume.
There have been two papers on the positions of the poles of Binary star orbits. One by Professor Turner and Mr. Lewis in M.N., 1907 June, where 59 orbits are discussed and the evidence found to slightly favour the view that their poles lie near the Galaxy. The other paper is by Karl Bohlin (Arkiv för Matematik, Astronomie och Fysik, Stockholm, Band 3, No. 19), wherein, by making choice of the alternative poles, the opposite conclusion is deduced.
The orbits computed are- Scorpii, 2173, 3121, 2 Herculis in A.N. 4169-70, and of a Centauri in No. 4189, all by Dr. Doberck, and of ẞ 612 by Mr. L. Semenow in Popular Astronomy, 1997 December.
Herr Zeipal gives parallax of Σ 443 as +"057 in A.N. 4188, and Chase, in A.J. 593, gives +"291 for 61 Cygni.
The principal event of the year in double star astronomy is the publication of Burnham's General Catalogue of Double Stars. This title includes two large volumes: (i.) the Catalogue proper; (ii.) Notes on the Stars in volume i. The catalogue, consisting of 330 pages, contains 13,665 double stars, arranged in order of R.A. (epoch 1880), and with the usual data for a working catalogue. Volume ii., consisting of 830 closely printed pages, gives a few selected early measures of the great majority of the stars contained in volume i., and a number of recent measures of many pairs not published elsewhere, together with notes sufficient to enable anyone to make out a working catalogue suitable to his geographical position and equipment, as all stars from the N. Pole down to 31° South Declination are included. At the same time a person wishing to make investigations is supplied with complete references which will enable him to collect all the observations relating to each particular pair. Obviously their inclusion would have necessitated another volume. When various catalogues of discoveries are thus brought together and the pairs arranged in order of R.A. in one general catalogue the discovery numbers do not run in any particular order, and it becomes difficult to find a pair. Professor Burnham has, in vol. i., a compact table, very ingeniously arranged, which enables easy reference to be made to any pair, either in vol. i. or vol. ii. Thus, on the left hand are numbers from one upwards, and in the succeeding columns, under the heading of the discoverer, the reference number in the "General Catalogue." Suppose we wish to look up ẞ 151-opposite 151, under Burnham,
is the reference. This table is not described in the introduction, and may well be overlooked. It also gives at once the number of pairs discovered by any observer. The catalogue has been published by the Carnegie Institute and freely distributed, and Professor Burnham is to be congratulated on the completion of so great and important a work. Reviews of the work are in various journals; and an appeal is made for measures of the wider pairs from the Astrographic plates.
The rate of discovery of new variable stars is well maintained in 1907, the last number allotted officially in the A.N. being 180, which represents the number of announcements during the year.
As usual, Harvard College Observatory shares very largely in this work, the principal notices being as follows:
Independently of the above, Harvard College Observatory Annals, vol. lx. part 4, refers to 1777 variables discovered in the two Magellanic Clouds, some of which have been previously announced. Part 5 gives particulars of 10 new Algol type variables, all south of decl. – 15°.
H.C.O. Circular 127 describes a practical method of search for variables of moderate brightness by superposing a negative upon a contact print of a second negative, covering the same region of the sky, but taken at a different date from the first. These photographs are large; that is, each covers a portion of the sky about 30 square, there being 55 maps for the whole sky. Already a considerable number of new variables have been brought to light, as indicated above; and a continuation of the scheme will probably result in approximately sweeping up all the known variables of a "moderate" degree of brightness.
Much work has recently been done at H.C.O. in continued photographic observations of known variable stars.
This observatory has issued a Second Catalogue of Variable Stars containing 1957 stars, including those in globular clusters. If we add the 1791 variables found in the Magellanic clouds, we get a total of 3748 known variables, of which considerably more than half have been found at Harvard. The full and accurate details of each star, together with a series of interesting remarks, critical and historical, render this undoubtedly the leading work of reference on the subject.
Vol. lvii. part 1, Annals H.C.O., contains the observations of 75 classical variables of long period, made by the "method of Argelander," during the years 1902-1905 inclusive. The results of the observations are also given in the shape of dates of maxima and minima, as well as full details of the light curves, etc.
During the past year has been published series iv. of the Atlas Stellarum Variabilium by the Rev. Father J. G. Hagen, S.J. This fine work represents the practical completion of the atlas, which must be the handbook for all observers of variables. It is on the same general lines as the preceding series, and contains 100 variables of various types, whose minima can be followed in telescopes of moderate size. For each star there is a beautifully printed chart, quarto size, giving the telescopic vicinity of the variable, the lines of R.A. and Dec. being in red, and a separate list of comparison stars, the magnitudes of which have been determined with great care. It would take up too much space here to do full justice to this meritorious work, the publication of which marks an epoch in the history of variable star research. It may be added that series v. of the Atlas, which has not been referred to in these notes, and which contains 49 stars whose minimum is below 7m, was published in 1906.
In addition to the foregoing, when account is taken of the work done in this country and on the Continent in 1907, it is plain that the department of Stellar Variation continues to occupy an important position in astronomical work.
E. E. M.
A very noteworthy addition to our knowledge of the parallaxes of stars is contained in the Yale Observatory Transactions, vol. ii. pt. 1, published towards the end of 1906. An extensive list of parallaxes, all determined on a uniform plan and with approximately the same degree of trustworthiness, is provided. The list consists of 163 stars, the observations being made by Dr. Chase, Mr. Smith, and Dr. Elkin, using a heliometer. Some idea of the magnitude of the undertaking may be gathered from the fact that it had been in progress for thirteen years. With a very few exceptions the stars selected were those having proper motions exceeding 40" per century, and not hitherto observed for parallax. It is noteworthy that not a single parallax exceeding o" 20 was found; the mean parallax was about o" 05. In general
the results appear to confirm Professor Kapteyn's tables of the mean parallax corresponding to given magnitude and proper motion. The deduced values of the linear velocities of the stars are on the average considerably higher than the mean velocities of stars deduced from line-of-sight determinations with the spectroscope; but it is pointed out that this is only to be expected, seeing that the stars were specially selected on account of their large apparent motions.
At the meeting of the British Association at Leicester, Sir David Gill devoted a large part of his presidential address to the subject of stellar distribution and the structure of the universe. Besides giving a general survey of the subject, his address included some unpublished results by Professor Kapteyn as to the distribution of stars in space and their luminosities, revising his earlier estimates, though not changing their general character.
In Groningen Publications, No. 18, Professor Kapteyn collects and compares all the available data as to the numbers of stars of various magnitudes in different parts of the sky. The difficulty of reducing the estimates of magnitude made by the different observers to a common standard, so as to render the enumerations of stars strictly comparable, is naturally very great, but seems to have been successfully overcome. The principal result of the paper is an empirical formula exhibiting the number of stars per square degree as a function of the magnitude and galactic latitude. Professor Kapteyn concludes, moreover, that, except in the immediate neighbourhood of the Milky Way, the distribution of the stars does not vary to any great extent with the galactic longitude. This must be taken to indicate that there is little important clustering of the stars except in the Milky Way.
In Monthly Notices, 1907 December, the mean distances of the stars of Groombridge's Catalogue are examined from the standpoint of the hypothesis of two star-drifts. Further evidence is given to show that the two drifts must be at sensibly the same mean distance from us, and that accordingly they must permeate one another. It also appears that the mean distance of these stars increases continually as we proceed from the galactic pole to the galactic equator. This is in accordance with the view that the apparently closer aggregation of stars in the galactic plane is not due to a clustering of the nearer stars, but to the fact that additional more distant stars are visible in those directions.
Professor Comstock continues his investigations on the solar motion relative to the very faint stars in Astronomical Journal, No. 591. He has now available proper motions of 149 stars, for the most part between the ninth and twelfth magnitudes, derived from double-star measures. From these he derives a position of the solar apex, R.A. 20, Dec. +54°. The most noteworthy feature is the high declination of the apex. Other investigators have noticed a progressive increase of the declination as fainter stars are used, so that this result, derived from stars fainter than had hitherto been considered, is not unexpected. The same author contributes a paper
on the "Luminosity of the Fixed Stars" to Astronomical Journal, No. 597
Dr. K. Schwarzschild (Nachrichten der K. Gesell. der Wissen. zu Göttingen, 1907) has discussed the law of distribution of the motions of the stars. He accepts the recent conclusion that there are two strongly favoured directions of motion, which, when referred to the centre of gravity of the stars, must be directly opposite to one another. On this basis he puts forward a frequency law, which, while differing only slightly from that embodied in the two-drift hypothesis, is remarkably well adapted for mathematical treatment and calculation, and, moreover, regards the universe as a single instead of a dual system. According to Dr. Schwarzschild's law, the frequency of a velocity (u, v, w) is proportional to e-Au2-B(x2+w2), where A <B. This stands in much the same kind of relation to the Maxwellian law, e-Au2+2+2), that a prolate spheroid does to a sphere; this distribution may in fact be derived from the random distribution by increasing all the component velocities parallel to the axis of x in a certain ratio. This axis corresponds to the direction of relative motion of the two drifts on the other theory. A careful analysis of the Greenwich-Groombridge proper motions on the new theory shows a very satisfactory accordance between theory and observation. No suggestion is made in the paper as to a theoretical basis for the law proposed; presumably some such distribution might arise if the universe (or that part of it which is here concerned) had originally been in the form of a very elongated ellipsoid.
Astrographic Chart and Catalogue.
A. S. E.
Additions to the published Astrographic Catalogue have been made during the year by the following observatories :-Catania, Zone 51° N., oh to 3h R.A.; Potsdam, volume iv., Zone 32° N.; Oxford University, volume ii., containing the whole of Zone 30°, and volume iii., Zone 29; Paris, volume ii., Zone 23° N.; and Bordeaux, volume ii., Zone 16° N.,-the word "Zone" implying in all cases the plates whose centres are at the declinations named, and the stars included therefore lie between declinations approximately 1 less and greater. The second volume of the Greenwich Astrographic Catalogue, which completes the northern cap 65° to the pole, allotted to the Royal Observatory, is on the eve of publication, so that substantial progress is being made.
The above-named observatories have all published previous volumes except Catania, whose contribution, though entitled vol. v. part 1, is the first issued from that observatory. The scheme of this work follows that of the Helsingfors Catalogue, each plate being taken as a unit, and all the stars it contains measured. In the columns of the catalogue these measures are given, and with these, in parallel columns, their values when corrected by application of the plate constants. These corrected measures are con