542 Proceedings of Royal Society of Edinburgh. [sess. 
lower levels at the place of maximum impact. A central section 
through the star immediately after the catastrophe may therefore 
he represented by No. 1 of fig. 18, the ring ABA' B' showing the 
incandescent surface layers, and A being the locality of maximum 
impact. After the collision has passed over, the surface begins to 
cool, and the star will gradually arrive at the stage No. 2, where 
the surface at B has cooled down to darkness, while the surface 
at A, through more vigorous conduction, and perhaps convection 
of heat from the interior, may still be in a state of incandescence. 
Some time afterwards the stage No. 3 will be reached, where the 
incandescence is now limited to a small lenticular segment at A. 
In this way the star would gradually pass from a state of all- 
round incandescence to total obscurity. If, now, we suppose the 
1 . 2 3 
cL}.. 'IS 
star to possess a rotatory motion, by which the points A and B are 
successively brought into the line of sight, we would notice the 
following features of variability : At No. 1 a uniform gradual 
decrease of brightness ; at No. 2 the same, but in addition a periodic 
recurrence of pronounced maxima and minima, the former being 
much extended and covering the greater part of the period, the 
latter being indicated by abrupt and short inflections of the light 
curve ; at No. 3, protracted minima covering the greater part of the 
period and maxima of short duration, hence the reverse of No. 2. 
These three theoretical light-curves are also represented in fig. 1 8. 
They are in fair accordance with the observed phenomena. 
This assumption of an axial rotation advocated in my former 
paper is by no means improbable, since the impacts will doubtless 
impart a certain moment of momentum to the star nucleus. But 
it may perhaps seem unnecessary in the case of a double star, 
