140 RECORD OF SCIENCE FOR 1887 AND 1888. 



VARIABLE AND OOLOREU STARS. 



Chandler^ s catalogue of variable stars. — The most inipoi'taut work upon 

 variable stars since Sclioenfekl's " Zweiter Catalog," now thirteen years 

 old, is a new catalogue published by Mr. S. C. Chandler as Nos. 179 and 

 180 of the Astronomical Journal. In the absence of any later catalogue 

 from Schoenfeld this immediately takes its place as the standard, though 

 the author states that it is preliminary to a more complete catalogue 

 which will embody a series of observations and definitive investigations 

 now in hand. 



An analysis of the catalogue shows that of the 225 stars comprised 

 in it 160 are distinctly variable ; in 12 the periodic character is rather 

 uncertainly defined ; 14 are distinctly irregular j 12 belong to the so- 

 called novw, or have been seen at only one appearance; and the 27 re- 

 maining have been too little observed for the character of the variation 

 to be properly known. Of the 100 periodical variables, epochs of both 

 maximum and minimum are assigned for G3 ; maximum epochs alone 

 for 82; minimum ejjochs alone for 14, 9 of these being of the Algol 

 type, while in one the period alone is given. The elements of 124 stars 

 are the results of Mr. Chandler's own investigations ; 22 are taken from 

 Schoenfeld; and 14 from other computers after Mr. Chandler had care- 

 fully confirmed them. The systematic perturbations shown by many 

 of the periods have received attention, and the iurther study of this 

 subject promises important additions to our knowledge of the causes 

 of stellar variation. 



A useful novelty introduced in numbering the stars calls for unquali- 

 fied approval. Instead of giving them consecutive numbers each is dis- 

 tinguished by a number equal to one-tenth of the right ascension ex- 

 pressed in time-seconds for the equinox 1900.0. In this way the numer- 

 ation need not be disturbed by fresh discoveries. 



The catalogue gives in successive columns a serial number assigned 

 in the way Just described ; Schoenfeld's number; the right ascension 

 and declination for 1855, and the annual variations; the discoverer; 

 date of discov^ery ; redness on an arbitrary scale; magnitude at maxi- 

 mum and at minimum ; Greenwich mean time of maximum and mini- 

 mum; period; remarks; and approximate place for 1900. 



A very ingenious method of estimating the colors was employed by 

 Mr. Chandler; it consists in estimating the relative change in bright- 

 ness effected in two stars by the interposition, first, of a blue and then 

 of a red shade glass. If a red and a white star appear of the same 

 brightness, when viewed directly, the red star will seem the ftxinter 

 when the blue glass is interposed, but the brighter with the red glass; 

 and these differences of brightness can be very iirecisely estimated by 

 Argelander's method, and they thus afford definite measures of the 

 differences in color of the two stars on an arbitrary scale depending 

 upon the glasses employed. Mr. Chandler finds that the effect of 

 brightness upon the scale-estimates is imperceptible, at least between 



