540 
Proceedings of Royal Society of Edinburgh. [mss. 
dark lines appeared to grow in strength between 28th February 
and 8th March .... But after 8th March their decline was regu- 
lar and uninterrupted ; they slowly disappeared, together with the 
bright calcium line K. On 12th March they had lost their centres 
and appeared as well-defined double lines, separated by a thin clear 
reversal. The more refracted components were much the weaker, 
and were the first to disappear. They had lost much on the 16th, 
and were quite extinct on the 20th, when the red side components 
formed the series of sharp thin lines, which were seen for the last 
time on the 21st.” 
It appears from this quotation that in Nova Persei the two 
absorption-lines in fig. 14 have been of different intensity, the one 
less refracted being decidedly the stronger of the two. The con- 
sequence was that this line outlived its more refracted feebler 
neighbour, and that there was a stage when the intensity-curve 
of the bands showed the structure exhibited in fig. 16. Suppose 
now this state of matters to have lasted for some time, during 
which the continuous spectrum has more and more decreased in 
brightness. Under these circumstances the absorption-line would 
A 
A 
