ASTRONOMICAL PHENOMENA AND PROGRESS. 



49 





system are very nearly identical with those of 

 TO ( >|>liiuc.lii, while the mass of the latter is less 

 thiin that of tho former in the ratio of three 

 to five. 



Xiriut. From a discussion of the observa- 

 tions of the companion of Sirius, Dr. Auwers 

 has found the period of revolution to be 49 

 years and 146 days ; the semi-axis of the or- 

 bit, :t~ times the distance of the earth from the 

 sun ; and the eccentricity, 0.6148 somewhat 

 greater than that of Faye's comet. The mass 

 of tin' companion is half that of the principal 

 star ; or, more exactly, the mass of Sirius is 

 18.76, and that of the telescopic star 6.71, the 

 in.i-- of the sun being uuity. As the light of 

 Sirius, according to Sir John Herschel, is 324 

 times that of an average star of the sixth mag- 

 nitude, and as the satellite discovered by 

 Clarke is of the ninth or tenth magnitude, the 

 light of the latter must be much less than one- 

 thousandth part of that received from the prin- 

 cipal star. The facts seem to indicate a re- 

 markable difference between the physical con- 

 stitution of Sirius and its satellite. 



Procyon. It was stated, in our volume for 

 1874, that M. Otto Struve had discovered a 

 small companion of Procyon, by which it was 

 believed the anomalous motion of that star 

 might bo satisfactorily explained. Strangely 

 enough, however, the most diligent search for 

 this new star with the twenty-six-inch re- 

 fractor of the Washington Observatory has 

 been hitherto unsuccessful, although three 

 other companions have been distinctly recog- 

 nized by Profs. Newcomb and Holden ; their 

 distances from Procyon being 6", 9", and 10", 

 respectively. The difference of atmospheric 

 circumstances could scarcely explain the con- 

 tradictory character of the observations at 

 Pulkowa and Washington. "We must conclude, 

 therefore, that the observations of Struve were 

 somehow erroneous, or that the light of the 

 new star is variable. 



Cincinnati Catalogue of New Double Stars. 

 The search for new double stars has been 

 recently prosecuted with eminent success at 

 the Cincinnati Observatory. As a first result 

 of these labors, the director, Mr. Ormond 

 Stone, has distributed a catalogue of fifty, all 

 included in the zone between 8 and 40 south 

 declination. They vary in distance between 

 "1.8" and 8". The estimated magnitudes of 

 the components are given, together with their 

 distances asunder, and their angles of position. 



Variable Stars. Dr. Gould, Director of the 

 Cordova Observatory, has found the period of 

 a variable star in Mnsca to be less than that of 

 any other variable hitherto determined. This 

 star, at minimum, is entirely beyond the reach 

 of unassisted vision even in the sky of Cor- 

 dova, though at maximum it is distinctly visi- 

 ble. The period of variation is about thirty 

 hours. 



In February, 1876, M. Tisserand, Director 

 of the Observatory of Toulouse, undertook a 

 series of observations on the small stars near 

 VOL. xvi. i A 



the trapezium in Orion. The instrument ued 

 was the Foucault telescope of 81 inches aper- 

 ture, then recently mounted. Especial atten- 

 tion was given to those stars which M. O. 

 Struve had designated as variable, and not 

 only were the suspicions of the Pulkowa ob- 

 server for the most part confirmed, but in the 

 case of several other stars in which he had 

 detected no change variations of magnitude 

 were clearly indicated. The existence of so 

 many variable stars in this remarkable nebula 

 will be regarded by astronomers as a fact of 

 no ordinary interest and significance. 



The Pleiades. The report of the Council 

 of the Royal Astronomical Society to the 

 fifty-sixth annual meeting (1876) contains 

 the following statements in regard to the 

 Pleiades group, several members of which are 

 found to be variable : 



M. Wolf, of the Paris Observatory, has made a 

 series of measurements of this interesting group of 

 stars, including all visible through an object-glass 

 of 0.81 millimetre aperture. The exact positions of 

 the 58 stars observed by Bessel, referred to Eta 

 Tauri by differences of right ascension and polar 

 distance, are given in a table containing the meas- 

 surements of M. Wolf, compared with those of 

 Bessel reduced to January 1, 1874. The relative 

 magnitudes of these 53 principal stars have been 

 determined with very great care, in order to detect 

 any possible variation of brightness since Bessel's 

 observations. M. Wolf has been able to detect no 

 less than 499 stars around Eta Tauri, contained 

 within a rectangle of 135 minutes of arc in length 

 and 90 minutes' breadth. These vary from the third 

 to the fourteenth magnitude. The observed magni- 

 tudes have been compared with those in the cata- 

 logues of Jeauret, Lalande, Piuzzi, Bessel, and 

 Argelander; from which M. Wolf concludes that 

 among the eight principal stars of the group, 

 Merope and Atlas are decidedly variable, ana Mam 

 appears also to have increased in magnitude since 

 the observations of Piazzi and Bessel. The five 

 others show no evidence of variability, but some of 

 the smaller stars have certainly changed their rela- 

 tive brightness since the former observations. 



He concludes, from a comparison of the differ- 

 ences between his and Bessel's measurements of 

 the 58 principal stars, that the Pleiades form a group 

 whose members are physically connected one with 

 the other; and, moreover, there appears to exist in 

 the group a relative displacement of the stars, which 

 carries the greater number of them in a contrary 

 direction to the diurnal motion, slightly diminihh- 

 ing their polar distance. M. Wolf hopes that his two 

 years' observations may serve as a certain basis, at 

 a future period, for the determination of the proper 

 motion of the separate components forming the 

 Pleiades group. 



Speetroscopie Observations. Sir George B. 

 Airy, the astronomer roytil, has recently pub- 

 lished the results of spectroscopic observa- 

 tions made at Greenwich for determining the 

 motions of stars in the line of sight. The 

 velocity of approach or recession of the stars 

 observed is found by the displacements of the 

 lines of known elements in their spectra; the 

 estimated rates of motion being corrected for 

 the earth's velocity resolved in the direction 

 of the star. The rate of recession assigned to 

 Sirius by these observations is 27 miles per 

 second, or about 852,000,000 miles per annum 



