48 



ASTRONOMICAL PHENOMENA AND PROGRESS. 



seventh to the tenth magnitude during the 

 years 1866-'74 ; and that throughout the years 

 1875 and 1876 the magnitude had remained 

 nearly constant. But during the whole period 

 of ten and a half years variations of brightness 

 were observed through approximately regular 

 periods of 94 days. Thus, after the first sud- 

 den fall in 1866, the star again increased from 

 the seventh to the eighth magnitude in less 

 than five mouths. Both the length of the 

 period and the extent of the variation appear, 

 however, to be diminishing. The color of the 

 star has been constant a pale yellow. 



The New Star in Cygnus. On the 24th of 

 November, 1876,* Dr. Schmidt, of Athens, 

 noticed a new star, of the third magnitude, in 

 the constellation Cygnus. The three nights 

 immediately preceding had been cloudy, buf 

 the star had not become visible on the night of 

 the 20th. Astronomers throughout the world 

 were at once notified of the discovery, and the 

 object was diligently observed both in Europe 

 and America. Its apparent magnitude very 

 rapidly diminished from the date of its discov- 

 ery. In a few weeks it became invisible to the 

 naked eye, and in less than three months its 

 light was no greater than that of a star of the 

 tenth magnitude. 



The spectroscopic analysis of the light of 

 this star was undertaken by Cornu, Vogel, and 

 other astronomers. At first, and for some time 

 after its appearance, it exhibited a continuous 

 spectrum, with a number of bright hydrogen 

 lines, thus resembling the spectrum of the new 

 star in the Northern Crown. This spectrum 

 gradually changed, however, until it was found 

 to consist of a single bright line, corresponding 

 in position to the characteristic line of the gas- 

 eous nebulae. In short, Mr. Copeland's obser- 

 vations at the Dunecht observatory justify the 

 conclusion, according to Lord Lindsay, that 

 the star has been transformed into a planetary 

 nebula a process exactly the reverse of that 

 imagined by Laplace in his nebular hypothesis. 



Star Systems. The Monthly Notices of the 

 Royal Astronomical Society for January, 1877, 

 contains a paper by Mr. J. R. Hind on the orbit 

 of Alpha Centauri. By combining two sets 

 of measures of the angle of position made by 

 Lord Lindsay at the Mauritius in 1874, with 

 those of Sir John Herschel, Captain Jacob, and 

 Mr. Powell, and adopting the angle for 1752.2 

 given by Lacaille's right ascension and declina- 

 tion, Mr. Hind obtained the following elements : 



Peri-astron passage 



Node 



Node to perl-astron on orbit 



Inclination 



Eccentricity , 



Semi-axis major. 



1874.85 



21 48'.0 



59 82'.1 



82 18'.4 



0.6673 



21".797 



Period of revolution 85.042 years 



"With an annual parallax of 0".928, which is a 

 mean between Henderson's value, as corrected 

 by Peters, and that of Moesta, the mass of 

 the system is found to be greater than that of 



* The announcement of this discovery came too late for 

 our last volume. 



the sun in the ratio of 179 to 100, and the 

 semi-axis major of the orbit 23.49. 



Dr. Doberck, of Colonel Cooper's observato- 

 ry, Markree, Ireland, has been devoting special 

 attention for several years to the orbits of binary 

 stars. His elements of Omega Leonis and Eta 

 Cassiopese were given in our volume for 1876. 

 The periods of others, together with the eccen- 

 tricities of their orbits, as given in the "Trans- 

 actions of the Royal Irish Academy " and the 

 Astronomische Nachrichten, are as follows : 



Burnham's Double-Star Discoveries. The 

 American Journal of Science for July, 1877, 

 contains a paper by S. W. Burnham, Esq., of 

 Chicago, on his double-star discoveries made 

 with the 18^-inch Chicago refractor. The la- 

 bors of this distinguished observer, of which 

 honorable mention was made in our volumes 

 for 1875 and 1876, are still continued with inter- 

 esting results. No. 438 in his latest list, a star 

 which had been previously known as triple, is 

 now shown to be quintuple. No. 440, which 

 had also been recognized as a ternary system, 

 is proved to consist of seven members, " the 

 whole forming one of the finest multiple sys- 

 tems known." No. 442 is a system of at least 

 seven members : three comparatively large 

 stars, between the eighth and ninth magnitude, 

 with four very minute companions. Mr. Burn- 

 ham's list is continued in this paper to No. 452. 



In the last volume of the " Annals of the Ob- 

 servatory of Paris," M. Wolf gives the details 

 of several years' labor devoted to the Pleiades, 

 together with some interesting conclusions in 

 regard to the relations existing between the 

 members of the cluster. In this well-known 

 asterism, where the unassisted eye sees only 

 six stars, more than 600 have been observed 

 with the telescope, and nearly all have been 

 accurately mapped. In addition to this deter- 

 mination of their relative positions the com- 

 parative magnitudes of over 500 have been 

 carefully measured. Several very small nebu- 

 las have also been detected within the group, 

 and the light of many of the stars is certainly 

 variable. But one of the most interesting facts 

 established by M. Wolf is that the stars of the 

 cluster have the same proper motion leaving 

 no room to doubt their physical connection. 

 The discussion indicates, moreover, that their 

 orbital motions inter se, or about a common 

 centre, are extremely slow in comparison with 

 their progressive motion in space. 



Changes in Nebulae. In the American Jour- 

 nal of Science for December, 1877, Prof. E. S. 

 Holden, of Washington, presents evidence of 

 the proper motion of the Tritid Nebula, desig- 

 nated as No. 20 in Messier's catalogue. This 



