ASTRONOMY. 101 



sive, tbo totals are, for the former, 34,324, aiul for the latter, 34,119, 

 a difference which may reasonably be attributed to accidental circum- 

 stances. 



The whole discussion of the distribution of the stars will no doubt 

 be much facilitated by the application of photography. 



A writer in L'Astronomie has concluded that the total number of 

 stars in '' our nebula" — on the assumj)tion that the combined light of 

 the stars is equal to one-tenth that of the full moon — must be sixty-six 

 thousand million. 



NEBULA AND STAR CLUSTERS. 



New nehulcc. — Two lists, embracing 476 new nebuhie discovered with 

 the 20-inch equatorial of the Leander McCormick Observatory, have 

 been published in the Astronomical Journal (7 : 9, 57) by Professor 

 Stone. The observers were Professor Stone himself, Mr. Leavenworth, 

 and Mr. Muller. lu the earlier observations Herschel's abbreviations 

 were used to designate brightness and size. Afterwards numerical 

 magnitudes were employed to indicate brightness, assuming that the 

 faintest uebiUa visible in the 2G-inch refractor with power 167, is 16.3, 

 that being the theoretical limit for stars. The magnitudes given refer 

 to the nucleus, or, in case there is no nucleus, to the brightest part. 

 Still later the custom was instituted of estimating the diameters of the 

 nebul* in fractions of the diameter of the field, and from these deducing 

 their dimensions in minutes of arc. 



Dr. Swift has published (Astron. i^achr., 115: 153, 257; 116 : 33) cata- 

 logues 3, 4, and 5 of nebulfe discovered at the Warner Observatory. He 

 states in the report of the observatory that 540 nebulae have been dis- 

 covered up to January 1, 1887. Mr. Muller has found that fifteen of 

 " Catalogue iTo. 5 " have already been announced by other observers. 

 (Sid. Mess., 6: 83.) 



The Pleiades. — M. Rayet, in order to test the penetrating power of 

 the 14-inch Bordeaux equatorial, has made a revision of Wolf's chart 

 of the Pleiades, and has determined accurately the positions of 143 

 stars, most of them of the fourteenth or fifteenth magnitude, not given 

 by Wolf. 



The Henry brothers have also compared their photographs of the 

 Pleiades with Wolf's chart, and have been able to detect 1,421 stars 

 where Wolf shows but 625, the telescopes used beingof nearly the same 

 aperture. In order to avoid errors which might arise from impurities 

 in the photographic plate, three exposures, of an hour each, were made, 

 and the plate was shifted between exposures, so that three images of 

 each star are obtained, forming an equilateral triangle. Stars as faint 

 • as the sixteenth magnitude are dei>icted. All the stars of Wolf's chart 

 are found upon the photograph except ten, and these the Messrs. Henry 

 have been unable to find in the sky. A number of faint companions 

 have been detected close to several of the brightest stars of the group, 



