JuNi; 8, 1905J 



NA TURE 



135 



OUR ASTRONOMICAL COLUMN. 

 Photographic Realitv of the Martian Canals. — No. 

 4021 of the Astronomische Naclirichten contains a telegram 

 ■dated May 28 from Mr. Lowell to Prof. Pickering in 

 which the former states that several of the canals on Mars 

 have been photographed by Mr. Lampland. Amongst 

 ■others, Nilo Syrtis, Casius, X'exillum, Thoth, Cerberus, 

 Helicon, Sty.x, Chaos, and Liedeus (? IJbneus) are shown 

 on the negatives, some appearing on more than twenty 

 plates. 



Discovery of .Saturn's Tenth Satellite. — A brief note 

 in No. 4015- of the Aslronomische Naclirichten states that 

 Saturn's tenth satellite was discovered from an examin- 

 ation of several plates taken with the 24-inch Bruce tele- 

 scope which were selected from those used in the deter- 

 mination of the orbit of Phcebe. 



The new satellite appears on thirteen plates. The 

 orbital motion is direct and the period is twenty-one days, 

 therefore the satellite is apparently a little nearer to Saturn 

 than is Hyperion. 



Jupiter's Sixth and Seventh Satellites. — .-^n abstract 

 from vol. xvii. of the Publications of the Astronomical 

 Society of the Pacific, appearing in No. 4015 of the Astro- 

 nomischc Nachrichtcn, contains an account by Prof. Perrine 

 of the observations so far made of Jupiter's sixth and 

 seventh satellites. 



The former can be photographed in ten minutes with 

 the Crossley reflector, and thirty-six plates have been 

 obtained. A preliminary investigation of the orbit shows 

 that the inclination to the ecliptic and the planet's equator 

 is about 30°, and that the satellite has a period of about 

 250 days, with a mean distance from the planet of 7,000,000 

 miles. The direction of the orbital motion still remains 

 uncertain. The brightness of the satellite indicates a 

 diameter of about 100 miles, or less. 



On examining the plates taken for the sixth satellite 

 on January 2, 3, and 4, a much fainter object, also 

 apparently belonging to Jupiter, was discovered, which was 

 then situated N. and W. of, and was moving towards, the 

 planet. Subsequent observations, which, owing to the 

 satellite's faintness, were much more difficult to make than 

 in the case of the sixth satellite, confirmed its dependence 

 upon Jupiter. This object was not shown on the negatives 

 taken for the sixth satellite during December, being just 

 outside their field, but altogether twenty observations have 

 been made, the last on March 9. 



.Apparently the orbit of the seventh satellite is quite 

 eccentric, with a mean distance from the planet of about 

 6,000,000 miles and a period of about 200 days. The 

 inclination of the orbit to the plane of Jupiter's equator 

 is about 30°, but the direction of the orbital motion is 

 as yet undetermined. The photographic magnitude of the 

 seventh satellite is not brighter than the sixteenth, and 

 on comparing this with the magnitudes of other satellites 

 and of asteroids a diameter of about 35 miles is deduced. 



Prof. Perrine suggests that the large inclination of their 

 orbits indicates that neither of these bodies were originally 

 members of Jupiter's family, but have been " captured " 

 by the planet. 



Stars with Spectra of the Orion Type. — In No. 2, 

 vol. Ivi., of the Aiinah of the Harvard College Observatory, 

 the distribution of stars having class E or Orion-type 

 spectra is discussed, and all known stars of this type 

 placed in a catalogue, in order of R.A., the position 

 (19000), magnitude, exact type of spectrum, and the 

 galactic longitude and latitude being given for each star. 

 Considerably more than 30,000 spectra have been examined 

 by Mrs. Fleming in connection with the Henry Draper 

 memorial work, and of these .S03 are included in the pre- 

 sent catalogue. 



As a distinctive feature of these stars is the helium 

 indicated in their spectra, the allocation of them with 

 regard to galactic longitude and latitude really indicates 

 the distribution of helium in the universe. On thus 

 classifying them, it is found that on dividing the sky into 

 equal areas the galactic latitudes of which are included 

 between -1-90° and -hjo", -1-30° and 0°, 0° and —30°, and 

 — 30° and —90°, the numbers of well marked helium stars 

 in these divisions are 22, 219, 509, and 53, or 3, 27, 63, 



NO 1858, VOL. 72] 



and 7 per cent, of the total respectively, nine-tenths of 

 them being within 30° of the galactic equator. .A 

 congregation in certain galactic longitudes is also in-> 

 dicated. Thus between ibo° and 340° there are 613, or 

 78 per cent, of the total, of these stars. .About one-quarter 

 of the whole number are contained in four regions having 

 a total area of 790 square degrees, or less than one-fiftieth 

 of the sky. One of these four regions is near to the 

 variable star I Carina;, and lies almost wholly within the 

 constellation Argus. As this Argus region contains nearly 

 three times as many " Orion " stars as does the Orion 

 region. Prof. Pickering suggests that " Argus " stars 

 would have been a more suitable generic name for the 

 class of stars having spectra of this (B) type. He states, 

 however, that the nebula of Orion appears to be the start- 

 ing point, or origin, of class B stars, twenty of which are 

 situated within 1° of Orionis, that is to say, nearly as 

 many as are contained in the region between galactic 

 latitudes -1-30° and -1-90°, although the area of the latter 

 region is three thousand times as great. 



Arranging them according to magnitude, it is found that 

 most of this class are bright stars, only i in 20 being of 

 the sixth or fainter magnitudes. 



The Motion of the Tail of Borrelly's Comet (1903 iv). 

 — From the examination of a number of photographs 

 obtained by different observers during July, 1903, Prof. 

 Jaegermann, Moscow, has compared the relative motions 

 of the different sections of the tail of comet 1903 iv in 

 regard to the movements of the comet's nucleus and to 

 the sun. After analysing the velocities and movements de- 

 termined, he has arrived at the conclusion that in this 

 case light-pressure, acting in the sense of Arrhenius's 

 hypothesis, was not the determining factor in the formation 

 of the several tails, for a pressure sixty times greater than 

 gravity would have to be assumed. If the light-pressure 

 hypothesis be retained, the assumption must be made, 

 according to Bredichin's idea, that the tail-matter con- 

 sisted of gaseous molecules, and that its illumination was 

 due to the fluorescence of highly illuminated gases, such 

 as has been experimentally demonstrated by Lommcl, 

 Wiedemann, and Schmidt. 



The existence of a repulsive force, other than light- 

 pressure, was demonstrated by Bredichin in comet 

 Rordame (1893 ii), by Prof. W. H. Pickering in comet 

 Swift, and was confirmed by Prof. Jaegermann in a pre- 

 liminary investigation concerning the denser parts of the 

 tail of comet Swift, 1892 i. 



Double Star Observations. — The results of a series of 

 observations of double stars made at Kirkwood (Indiana) 

 Observatory are given in No. 4022 of the Astrononiische 

 Naclirichten. The observations were made by Mr. J. A. 

 Miller and Prof. \V. .\. Cogshall with a 12-inch refractor, 

 and the B.D. and .\.G. numbers, the 1875 position, the 

 magnitudes, and the measured position-angle and distance 

 are given for each of 114 double stars. 



The objects observed were selected from those noted as 

 double by the Leipzig observers when preparing the A.G. 

 catalogue for the zone +10° to -1-15°, and, with few excep- 

 tions, they have not been measured elsewhere. Some few 

 stars suspected by the Leipzig observers as duplicate could 

 not be seen as such by the Kirkwood observers, and one 

 or two of the sets of measures refer to newly discovered 

 double stars. 



TffE ROYAL OBSERVATORY, GREENWICH. 

 (^N Saturday last, June 3, the Board of \'isitors made 

 ^-^ their annual inspection of the Royal Observatory, 

 Greenwich, but unfortunately, through ill-health, the 

 Astronomer Royal was not able to be present. The follow- 

 ing is a brief abstract of the report which was submitted 

 to the visitors. 



\^ery great progress has been made in the observation 

 of the reference stars for the Greenwich section of the 

 Astrographic Catalogue, about 9500 observations of R..A. 

 and N.P.D. having been added during the year. The 

 comparatively few observations required to secure five 

 observations of each of the reference stars (more than 

 10,000 in number) will easily be obtained by the end of 

 the vear, as there are onlv 5 stars requiring three observ- 



