196 ASTRONOMY. 



stars should be near together. The focal length of the telescope is 

 about seventeeu feet, aud its available aperture is limited by the size 

 of the prisms to about an inch. Observatious were made on thirteen 

 nights, from September 29, 1880, to January 1, 1881. Three settings of 

 each of the four positions of the Nicol constituted a set; the total num- 

 ber of sets was 230. Seven minima were observed, and the probable 

 ' error of a single minimum is 3.8 minutes, while Schmidt gives the 

 probable error of a minimum observed by Argelander equal to G min- 

 utes, aud of those of Schonfeld 4.6 minutes. A comparison is made 

 between the light curves found by Schonfeld, and at Harvard College 

 Observatory, and the photometric and naked-eye methods are found to 

 agree closely. For the observation of Ceraski's variable star -fSl^ 

 ISTo. 25, the photometer was attaclied to the 15 inch refractor, on account 

 of the faintness of the star. Two hundred and seventy-three sets of 

 measures were made, and five minima were observed. The average 

 probable error of a minimum is 1.3 minute, or about one-third of that 

 of /3 Persei, which was to be expected since the rate of variation of the 

 stars is about as three to one. Some interesting theoretical conclusions 

 are drawn from the.resulting light curve. For about an hour and a half 

 the light remains sensibly constant at 0.110, or about one-ninth of its full 

 intensity. This interval is over one-third of that during which the ligljt 

 is increasing or diminishing. If the variation in light is admitted to 

 be-due to a dark eclipsing satellite, the diameter of the latter must be 

 v'l— 0.110 = 0.943 of that of the star, in order to sufficiently reduce 

 the light. A somewhat smaller diameter is possible, if we admit that 

 the star, like our Sun, is darker near the edges than in the center. But 

 the difference cannot be great, or it would show itself in other ways. 

 The longest period of uniform minimum light would occur if the satel- 

 lite produced a central annular eclipse. In this case if the motion was 

 uniform, the duration of the minimum light would equal only one-ninth 

 of that of increase or decrease. The effect of curvature or ellipticity 

 of the path would not greatly affect this conclusion. A very great ellip- 

 ticity is not admissible, or at the periastron the satellite would strike 

 the star. We are, therefore, obliged to admit that the star is entirely 

 covered by the satellite, and that the light during the minimum is either 

 due to some proj)er light of the satellite, or is to be explained by admit- 

 ting that the satellite consists of a cloud of meteors so scattered that 

 about one-ninth of the light of the star can pass through the central 

 jiortions. 



On September 13, 1881, a red star was noticed at the Harvard College 

 Observatory in E. A. IG^ 31™.5, Dec. + 72° 32'. From the similarity 

 of its spectrum to that of several known variable stars, it was presumed 

 •to be variable; and the suspicion was confirmed, both by its absence 

 from the catalogues and by subsequent observation, which showed that 

 its brightness was increasing. 



