or ARTS AND SCIENCES. 257 



INVE8T10ATION8 ON I/IOHT AND IIeAT, PUnUHHED WITH AN APPROPBUTION FROM TUB 



RUMFORD Fund. 



xin. 



VARIABLE STARS OF SHORT PERIOD. 

 By Edward C. Pickering. 



Presented February 9, 1881. 



In a recent communication to this Academy * the following classifica- 

 tion of the variable stars was proposed : — 



I. Temporary stars. Examples, Tycho Brahe's star of 1572, new 

 star in Corona, 18G6. 



II. Stars undergoing great variations in light in periods of several 

 months or years. Examples, o Ceti and ^ Gygni. 



III. Stars undergoing slight changes according to laws as yet un- 

 known. Examples, a Orionis and a Cassiopeice. 



IV. Stars whose light is Continually varying, but the changes are 

 repeated with great regularity in a period not exceeding a few days. 

 Examples, ft LyrcE and 8 Cephei. 



V. Stars which every few days undergo for a few hours a remark- 

 able diminution in light, this phenomenon recurring with great regu- 

 larity. Examples, (i Persei and S Cancri. 



A discussion was given, in the article referred to, of the stars of 

 the last class. It was shown that in the case of jB Persei at least, the 

 observed variations could be very satisfactorily explained by the theory 

 that the reduction in light was caused by a dark eclipsing satellite. 

 The dimensions of this satellite and of its orbit were then computed. 

 The variations of the stars of the fourth class will be considered in 

 the present paper. Both of these papers must be regarded as prelimi- 

 nary, rather than final, discussions. Observations are now in progress 

 at the Harvard College Observatory which greatly increase the preci- 

 sion of our knowledge of many of the constants involved. When 

 these are completed, a revision of the whole investigation is much to 

 be desired. To avoid all prejudice, the present papers are made to 



* Proc. Amer. Acad., xvi. 1. 



VOL. XVI. (n. 8. VIII.) 17 



