6 ART. 19. — N. ICHINOHE I 



the period is extending to one year or so and if Ave take s 

 Aurigae in this class of variables, the period is extended to 

 twenty seven years and more. Thus, the length of the period 

 will not also be the foundation of the classification. Therefore, 

 we must be content to classify the variables according to the 

 appearance of the light-curve, till the day will arrive as we can 

 distinguish all the eclipsing stars from the other variables. Then, 

 1 formulated the following definitions for the Algol-variables. 

 I. An Algol is a variable star whose light-curve shows the 

 stationary maximum or normal brightness with an eclips- 

 ing phenomenon and the duration, in which the normal 

 brightness continues, is comparable with the whole dura- 

 tion in which the eclipse takes place, or far surpasses 

 it; while the period, the time-interval from a minimum 

 to the succeeding one, is practically constant. 

 II. riie eclipse phenomenon begins by diminishing of light 

 from the normal state and reaches a certain minimum 

 brightness. Then the star begins to regain the light 

 through the minimum which continues some time till it 

 reaches the normal. 



III. The light-curve of Algol has the decreasing and ascending 

 branches, which are not very flir from symmetry with 

 respect to the middle of the minimum, which continues 

 some time. 



IV. The normal brightness is, sometimes, interrupted by a 

 secondary minimum without destroying the condition of 

 the stationary maximum. 



V. Elements of an Algol are subjected to certain j^erturba- 

 tions whose laws are not yet accurately discovered. 



