132 ASTRONOMY FOR 1889, 1890. 



julditioiis and corroctious to the elements of the catalogue; and (3) a 

 list of stars probably variable, but whose variability needs further con- 

 linnation belorc (k'linitive letters can be assigned. Tne attention of 

 observers is directed to this list. 



Taking his catalogue of 1888 as a basis, Mr. Chandler has made an 

 investigation of the relation existing between the lengths of the j^-riods 

 and the number of the variables; their color, range of fluctuation, 

 forms of light curves, irregularities of periods and of light variations. 

 Periods under 20 days predominate, while for the long-period stars a 

 well-marked maximum is indicated about a period of 320 days. AVitli 

 regard to color, the redder the tiut the longer the period; and with 

 regard to range of liuctuation, while it is probable that there is a de- 

 pendence of range upon the duration of the period, the relation is not 

 one of strict proportionality of range to period. It furthermore appears 

 that the average ratio of increase to decrease for stars with periods less 

 than 100 days is about 0.05; between 100 and 200 days it is slightly in 

 excess of unity ; it then declines as the periods lengthen ; at first, grad- 

 ually, but in the neighborhood of a year, with extraordinary sudden- 

 ness, recovering as quickly until it again exceeds unity in the group of 

 extremely long periods. In the case of the numerical laws of the per- 

 turbations of the periods, Mr. Chandler remarks that his researches 

 are not yet complete, but that, broadly, in the case of long-period vari- 

 ables, the irregularities are periodic in their nature, and in the case of 

 those of short period, secular and exceptional. 



Ah/ol. — Prof. H. C. Vogel, of Potsdam, has published the results of 

 some interesting observations of the changes in the spectrum of Algol 

 at the times of the diminution and recovery of its light. These, whilst 

 fully confirming the view originally suggested by Goodricke, that the 

 periodic variability of this star is caused by the revolution of a dark 

 companion cutting off part of its light in the manner of an eclipse, and 

 the calculation of J'rofessor Pickering that the diameter of the compan- 

 ion amounts to about eight-tenths of that of the principal star, have 

 enabled Professor Vogel to obtain approximate values of the mutual dis- 

 tance and actual sizes and masses of the two stars, as well as of their 

 orbital velocities round their common center of gravity. He finds, in 

 fact, that their diameters are probably about 1,080,000 and 850,000 

 English miles respectively; that the distanceof their centers from each 

 other amounts to about 3,290,000 milets, and that the orbital velocity of 

 Algol is about 27, whilst that of its companion is about 5(5 miles. The 

 mass of the former he determines to be about double that of the latter, 

 the one beingapproximately four-ninths and the otiier two-ninths of the 

 sun's mass. It is not necessary, he remarks, to suppose that the com- 

 l)anion is absolutely opacjue, but only that its light is very much feeb- 

 ler than that of the i)rincipal star. 



It may be achlcd tiiat tlu' (Jrecnwich observations confirm Dr. Vogel's 

 conclusion of the motion of the star in a small orbit. 



