THE SPECTRUM OF NOVA PERSEI AND THE STRUCTURE OF ITS BANDS. 263 
6. The Continuous Spectrum.—The question whether the continuous spectrum has 
a share in these radiations is settled by photo-plate No. 1, which was orthochromatie. 
There are five minima recorded between wave-length 496 and 538, whose intensities 
range between 0 and 0°3 degrees. I obtain the reduction for relative sensitiveness for 
different wave-leneths from a series of exposures on the sky spectrum. On the 
supposition that the intensity curves of the spectrum of the sky and of the star are 
identical, the intensity of the continuous spectrum of the star does not reach 1 degree 
within the area photographed, and probably is less, considering the observed colour of 
the star. Not to complicate the problem unnecessarily, I have disregarded the 
continuous spectrum, and it will be scen from what follows that the only effect this 
omission can have on the result is to increase slightly the calculated degrees of 
intensity of the bands. 
7. Mean Structure of the Bands.—The continuous spectrum being very faint, the 
difference under discussion must be caused by superposed bands. From the plates 
taken after August I shall prove that not only the H-bands, but all the bands, are 
similar. I assume that the same holds good for the earlier plates, and that therefore 
the superposed bands are similar to the H-bands. The unknown structure of the bands 
thus enters not only the H-bands, but also the bands overlapping their ends, and that 
structure must be so determined as to give the observed degree of intensity. In the 
solution of this problem two other questions are involved: First, in what way does the 
intensity curve of the band vary if the intensity of its maximum alters? Secondly, 
what is the resultant intensity on my degree scale if two radiations which singly 
produce certain degrees of intensity on the photograph be superposed ? 
The two bands, A = 4902 to 4959 and A= 4981 to 5046, agree in extent and in position 
of their maxima with the bands calculated from the bands of Table IV. by formula (1), 
and the wave-lengths of their zero, \, are found respectively to be 4922 and 5016. I 
compared the observed degrees of the H,-band, which in first approximation served as 
standard, with those at corresponding points of the faint bands \,= 4922 and 5016, 
discarding the points where the bands overlap, and deduced by interpolation the 
relations given in Table VI. For instance, a band which has at different points the 
Taste VI.—Corresponding Degrees of Intensity. 
13 1] 9 7 5 3 i 
11 9°3 iGo 58 4°] 2°3 0°6 
9 | 75 6-1 4:6 31 17 0:2 
7 58 4:6 3°4 2°2 1:0 
5 4-1 31 2-2 1:3 04 
3 2°3 EY 1:0 0-4 
1 0°6 0-2 
