58 F. W. Yery — Nebulosity around Nova Persei. 



the differences between the vibration-numbers of the compo- 

 nents of the triplets in the spectra of many of the elements, for 

 example, ratio of intervals : zinc 2*07, magnesium (b line) 2*03, 

 oxygen 1'78 to 2-0, calcium 2-02, etc. 



An examination of the rate of expansion of the nebula shows 

 that, since the hundredth day from the outburst of the nova, 

 there has been a retardation, and probably an increasing retar- 

 dation, in the motion of the nebulous rings. I assume that the 

 nebula consists, in a general way, of two or more lemniscoidal 



O.OJ 



o.od 



0.05 

 0.04 

 0.03 

 0.02 



0.0/ 





joo zoo 300 <^a^s 



shells involving minor details of structure which find their 

 limit in the elliptical projection of equatorial circles of the 

 lemniscoids. Since the minor details are of vague shape and 

 difficult to locate with precision, I prefer to estimate the posi- 

 tions of the elliptical rings, and taking the mean of major and 

 minor semi-axes as varying with the successive loci of the 

 motion which traces the lemniscoidal figure, I obtain for the 

 rate of nebular expansion the values contained in the following 

 table : 





Time 



Mean 



Expansion — 





interval. 



radius. 



Mean daily rate 





0-36 days 



l'-85 



0'-0514 



Outer 



36-100 " 



5 -7 



-0602 



shell 



100-200 " 



11 -6 



-0590 





200-300 " 



14-9 



-0330 





0-36 " 



0-88 



-0244 



Inner 



36-100 " 



2 -8 



-0300 



shell 



100-200 '' 



5 -7 



-0280 





200-300 " 



V -4 



-0170 



The curves of the rates of expansion (fig. 2) differ totally from 

 that of matter moving outward under the retardation of the 

 attraction of a central mass (namely, velocity diminishing with 

 the inverse scpare root of the distance) ; but the motion is in 



