348 SCIENTIFIC RECORD FOB 1885. 



thus afforded of one of the markings on the Cambridge photograph 

 makes the others of more interest than seemed at first to belong to them. 

 There are indications of nebulous light about Merope; four short parallel 

 streaks directly to the south following side are particularly noticeable, 

 and a faint prolongation of diffuse light may be suspected towards the 

 south, in agreement with the descriptions usually given of the visible 

 nebula in that region. There is also a faint narrow streak of light pro- 

 jecting from Electra on the following side. All the bright stars are 

 surrounded by concentric bands, obviously due to effects of reflection 

 from the back of the plate and from the inner surfaces of the lenses. 

 These bands interfere to some extent with the appearances of nebulous 

 light above described, and are most conspicuous around Alcyone, as 

 would be expected from the brightness of that star. No nebulous light 

 is noticeable about Alcyone, Atlas, Pleione, or Taygeta." 



Professor Struve announces that he has seen the nebula about Maia 

 very distinctly with the great 30 inch refractor of the Pulkowa Ob- 

 servatory. We learn also from later reports that the nebula has been 

 seen and sketched at the Nice Observatory. 



Photographic study of the nebula of Orion. — Prof. E. C Pickering has 

 made a comparison of the results of photographic and eye observations 

 of this region, comparing the star magnitudes as given by the photo- 

 graphs of Dr. Draper and Mr. Common, with the catalogue of Profes- 

 sor Bond. His results will be found carefully tabulated in the twen- 

 tieth volume of the Proceedings of the American Academy. One of the 

 most important applications of the determination of photographic mag- 

 nitudes is to the measurement of the colors of the stars. The rays af- 

 fecting the photographic plate have in general a less wave length than 

 those to which the eye is most sensitive. It therefore follows that a 

 reddish star, that is, one in which the rays of great wave length pre 

 dominate, will appear relatively too faint in the photograph. A bluish 

 star is similarly indicated by a large negative residual (on comparison 

 with eye estimates). These residuals form a convenient measure of the 

 colors of the stars ; and Professor Pickering gives a list of ten led stars, 

 thus indicated on the plate, varying from 10-7 to 13-9 magnitude, ac- 

 cording to Bond, and ten blue stars, varying from 12-3 to 15-6 magni- 

 tude. "The faintest stars visible in the photograph have a photo- 

 graphic magnitude of about 15-0." 



Variability of a nebula. — ''The nebula near the star C Tauri seems to 

 present an interesting instance of variability of light. This nebula 

 was observed by Chacoruac at Paris on the 19th of October, 1885, sur- 

 rounding a star of the 11th magnitude, which had repeatedly been ob- 

 served in 1854, and also at Markree in January, 1850, without any nebu- 

 losity being noticed. In January, 1856, Chacoruac found this very 

 bright and conspicuous, resembling in its appearance a transparent 

 cloud, reflecting the light of C Tauri. But in November, 1862, he could 



