"NEW" AND VARIABLE STARS. 401 



drge, R. Leonis, etc. Mira Ceti varies from about the second 

 magnitude to a little below tbe ninth, with a mean period of 

 about 331 days from maximum to maximum. Owing to its un- 

 usual brilliancy at maximum, and the great range of its light- 

 fluctuations, this is perhaps the most interesting and remarkable 

 of all the variable stars. The period of Chi Cygni is about 406 

 days, and its variation from about the fourth to nearly the thir- 

 teenth magnitude. R. Hydrse varies from the fourth to the 

 eleventh mgnitude, with a period of about 437 days ; and R. Le- 

 onis from about the fifth to the tenth magnitude, with a period of 

 about 313 days. Most of the long-period variables are reddish 

 in color, and show a banded spectrum, which seems to be a char- 

 acteristic feature of this type of variable. Various theories have 

 been proposed to account for the variation of light in long-period 

 variables, but none of them are very satisfactory. The periodical 

 outbreak of sun-spots on a large scale has been suggested, and 

 also the clashing together of meteoric swarms revolving in an 

 elongated orbit ; but it must be confessed that the subject is still, 

 to a great extent, a matter of mystery. 



Class 3 includes the irregular variables that is, stars which 

 are undoubtedly variable, but have no regular periods. Some- 

 times these stars remain for long periods without any perceptible 

 change, while at other times their fluctuations of light are very 

 noticeable. Of these, perhaps the most remarkable are Mu Ce- 

 phei (Sir William Herschel's "Garnet Star"), Alpha Herculis, 

 Alpha Orionis (Betelgeuse), and Beta Pegasi. The variation is 

 usually small, not exceeding one magnitude. Like the regular 

 variables, these have also banded spectra. 



In Class 4 are some very interesting objects variable stars of 

 short period. The greater number of these have periods of under 

 eight days. The variation of light is generally small, but regu- 

 lar. In but few cases does it much exceed one magnitude, and in 

 several it is less. In some, as in Beta Lyrse, Zeta Geminorum, 

 and Eta Aquilse, all the light-changes may be observed with the 

 naked eye, while in others an opera-glass is necessary to follow 

 the fluctuations. 



In Class 5 are placed stars of the Algol type. These are the 

 rarest of the regular variables, only ten having been hitherto de- 

 tected. In these stars the light remains constant, or nearly so, 

 for the greater portion of the period. A sudden diminution of 

 brightness then commences, and all the light-changes are com- 

 pleted in the course of a few hours, after which the star returns 

 to its normal brightness. The brightest of these remarkable stars 

 are Algol (Beta Persei), Lambda Tauri, and Delta Librse. The 

 others are much fainter, only two being visible to the naked eye 

 when at their normal brightness. A star of this class recently 



VOL. XXI. 31 



