574 



NA TURE 



[April 12, 1900 



OUR ASTRONOMICAL COLUMN. 



Rotation Period of Venus — A telegram just received 

 from Herr Backlund, through the Centralstelle at Kiel, reads as 

 follows : — '* From four spectrograms Belopolsky has been able 

 to confirm the short rotation period of Venus." 



Elliptic Elements of the Variable Y Cygni. — Prof. 

 N. C. Duner, of Upsala, has computed the elliptic elements of 

 the Algol Variable Y Cygni, and gives his results with a derived 

 ephemeris in the Astronomische Nachrichten, Bd. 152, No. 

 3633. 



Elements of Y Cygni. 



Epoch /„=i885-o + 342-893od. 



Anomalistic motion of apse line .. 01 = 0" '035928 



Eccentricity g = o°i4535 



Anomalistic revolution U = 2 •996933d; 



Semi-major axis A = 8"o 



Photometric Observations of Mercury during Solar 

 Eclipses. — Dr. G. Miiller, of Potsdam, has for some years 

 made systematic measurements of the brightness of the 

 planet Mercury for phase-angles varying from 50° to 120°. 

 No observations could be made nearer than 50° from 

 che sun. From his results, he finds that the relation giving 

 the light-curve of Mercury is almost identical with that 

 obtained by other workers in the case of the moon. This 

 similarity could be very severely tested if the brightness of the 

 planet could be determined directly at the phase-angles from 

 0° to 50°. In the Asirophysical Joiimal xi. pp. 144-147, he 

 suggests that an excellent opportunity to carry out this work 

 will be presented during the coming total eclipse in May 1900. 

 The phase-angle for Mercury at the time of the eclipse will be 

 about 7°, and its angular distance from the sun about 2°. 



Venus will be the most suitable object for comparison, being 

 about 40° east of the sun at the time of the eclipse, with a phase- 

 angle of 113°. It will be advisable to use small objectives of 

 very short focus, so that the images of the planets may appear 

 as practically points of light ; it is also desirable to employ 

 only those photometers with which (as is the case of Zollner's) 

 the effect of the different brightness of sky background is 

 eliminated. 



Variation of Latitude.— Prof. Th. Albrecht, of Potsdam, 

 gives a resume, in the Astronomische Nachrichten, Bd. 152, 

 No. 3633, of his continued discussion of the results obtained at 

 various stations for the motion of the earth's pole. The obser- 

 vations have been made at the following stations : — Tokyo, 

 Kasan, Moscow, Pulkowa, Prague, Potsdam, Lyons, New York, 

 Philadelphia and Washington, during various periods extend- 

 ing from 1892-3 to 1899 9. The co-ordinates of the pole as 

 deduced from these new results are plotted in continuation of 

 Prof. Albrecht's former curve. During the period 1895 "o to 

 i895'6, the motion appears from the curve to have been in the 

 opposite direction to that followed since, although several com- 

 plete revolutions have taken place. 



Planetary Work at the Manora Observatory.— Herr 

 Leo Brenner communicates to the Naturxvissenschaftliche 

 Wqchenschrift, Bd. xv. No. 13, pp. 145-150, his report of the 

 work done at the Manora Observatory during the past year. 

 Besides the drawings of the planetary markings, which is the 

 chief undertaking of the institution, the scope of routine work 

 included observations of the sun, zodiacal light, double stars and 

 meteors. The report is illustrated by twenty-eight reproduc- 

 tions of drawings of the planets Mars, Jupiter and Saturn, 

 showing the various markings mentioned in the text. The spots 

 on the ball of Saturn appear to have been continually seen. 



THE DEVELOPMENT OF ASTRONOMY IN 



AMERICA. 2: 

 QIXTY years ago the United atates had scarcely a single 

 "^ observatory properly equipped for the pursuit of astro- 

 nomical studies. To-day that country is possessed of the finest 

 observatories in the world, manned by observers of the greatest 

 skill, who devote themselves untiringly to the advancement of 

 the oldest of the sciences. 



The success of the American astronomers during this short 

 period has been remarkable. To them we owe important dis- 

 coveries and precious records in nearly every branch of theo- 

 retical and practical astronomy, and especially of late years in 

 NO. 1589, VOL. 61 J 



the department of astronomical physics. It is impossible here 

 to recount the whole fruits of their labours, but it is worth while 

 to recall a few of the results which we owe to their industry. 



The first striking discovery in America was that of Hyperion, 

 the seventh satellite of Saturn, by G. P. Bond, in 1848. In the 

 same line of work, Hall was rewarded in 1877 by the discovery 

 of the tiny satellites of Mars, and more recently Barnard 

 astonished the world by his detection of the fifth satellite of 

 Jupiter, while Pickering claims to have established the existence 

 of a ninth satellite of Saturn. In planetary studies generally, 

 the Americans have been well to the front, and we have seen 

 the unusual spectacle of a powerful refractor primarily devoted 

 with marked success, by Mr. Lowell, to the delineation of the 

 surfaces of our nearest planetary neighbours. Numerous mea- 

 surements of the dimensions of the various members of the solar 

 system have also been made, and the theory of their motions has 

 been greatly advanced, notably by the well-known investigations 

 of Newcomb. 



Cometary astronomy has likewise benefited by their zeal, 

 many new discoveries having been made, and the orbits of a 

 large number calculated ; in this branch the Americans are now 

 more active than ever, no less than six of the seven new comets 

 discovered in 1898 being to their credit. Important investiga- 

 tions relating to meteorites and the orbits of meteor swarms 

 have also been carried out, and the name of Prof H. A. Newton 

 will always be associated with this department of astronomical 

 research. 



Sidereal astronomy has been enriched by numerous star cata- 

 logues, and double-star observation has been brought to a high 

 standard of perfection by the assiduous efforts of Burnham, 

 Hall and See; while Pickering's "Harvard Photometry" has 

 given us an invaluable record of the magnitudes of thousands 

 of the brighter stars. The study of variable stars has also been 

 very productive, our most important catalogue of these objects 

 being due to Chandler, while a unique atlas of variable stars is 

 in course of publication by Prof. Hagen ; here, as in many other 

 directions. Prof. Pickering's ingenuity has been displayed, and 

 he has shown among other things how variables of short period 

 can be readily detected, and the changes studied, by photo- 

 graphic means. 



Our catalogues of nebulae discovered since the time of the 

 Herschels include a large number of entries to the credit of 

 American observers, Lewis Swift having specially distinguished 

 himself in this field of work. 



Notable work has also been done in the domain of solar 

 physics. Young's observations of the chromospheric spectrum 

 have only been surpassed by the most recent eclipse photo- 

 graphs, and Prof. Hale was the first to initiate a regular photo- 

 graphic record of the forms of the chromosphere and promi- 

 nences. Quite recently, the great telescope of the Yerkes 

 Observatory has been used for a very detailed examination of the 

 spectrum of the chromosphere, and even the most minute 

 structure of the carbon flutings in the green has been success- 

 fully observed, ^'o Prof Rowland we owe a great catalogue of 

 close upon twenty thousand of the Fraunhofer lines, the positions 

 of which are stated with a degree of accuracy never before 

 attempted ; and physicists and astronomers throughout the world 

 are indebted to this observer for the magnificent diffraction 

 gratings which his skill has placed at their disposal. By the 

 invention of the bolometer, Langley has opened up a new region 

 of the spectrum, and has made numerous important observations 

 by its aid. At the present time a committee of American 

 astronomers is organising the work to be undertaken during the 

 total eclipse of the sun next May, and from a preliminary report 

 which has been issued we gather that they are fully alive to the 

 opportunities which such an event affords. 



Astronomy owes an immense debt to photography, and it 

 should not be forgotten that the first photographic impression 

 of a star was obtained on the other side of the Atlantic, by 

 Prof. Bond, in 1850. Among those who early recognised the 

 possibilities of astronomical photography was Rutherfurd, of 

 New York, who obtained numerous pictures of the sun, moon 

 and stars in the early seventies, the full value of which has 

 only lately begun to appear. It was there also that Dr. 

 Draper, in 1872, secured the first photograph of a stellar spec- 

 trum which revealed anything relating to the composition of a 

 star, and that Barnard, in 1892, made the first discovery of a 

 comet by the aid of the camera. 



The story, however, by no means ends with this pioneer 

 work ; celestial photography has been pursued with the 



