735 



20 16.307 9.107^) 



Tlie intensity thus diminislies slowlj at tirst and then taster and 

 faster, but the velocity soon reaches a maximum, when the star 

 has fallen rather more than 1 magnitude beh)w the original intensity. 

 The velocity of decrease then becomes slower once moi-e and tinally 

 approaches a logarithmic curve. 



The slow decrease in the beginning is not observed in tiie new 

 stars, as the process of blazing np has not yet worked out then. 

 Botii Nova Persei and Nova Aquihie had their maximum one day 

 after they had readied the first magnitude, and Nova Persei 

 one day before that had already attained the 3'^^ magnitude. As 

 the starting-point t = we must not therefore take the moment 

 of maximum luminosity, but one or two days earlier. Then follows 

 a rapid decrease which, however, soon becomes slower and is then 

 accompanied by periodical variations. On comparing the observed 

 light-curve and the one here calculated they are found not to agree 

 during the further course of the change; the mean observed intensity 

 decreases much more slowly than according to the above calculation. 

 Evidently other influences are at work here, lying outside the simple 

 theory here given. It is therefore only foi" the first period of rapid 

 decrease of luminosity that agreement may be looked for. 



For Nova Persei we shall take 0,0 as the ideal maximum inten- 

 sity, a little highei' than the greatest brightness observed, because 

 for it the final stage of the blazing up overlaps the beginning of 

 the expansion, and for the ideal starting-point the 21^"^ of February. 

 The following values of At are then found from the values of ;/? — n>„ 

 on the smoothed obsei-vational lioht-curve. 



^) From 1.0 to 2.5 equation 5/> has been used, from 2.5 to 20 equation ba. 



