286 PROFESSOR L. BECKER ON 
possibility is not excluded that the March-April identification is wrong, and that both 
the earlier and the later bands belong to the same radiations. 
In the second half of the table appear the twelve corresponding lines which Campbell 
photographed in the spectra of five planetary nebule, and the range of their intensities 
in these five spectra, 1 standing for ‘‘ faint,” and 6 for “very bright.” Besides these, 
there are only two lines, \= 4662, intensity 1 to 4, and \=4744, intensity 2 to 4, 
which Campbell found present in each of the five nebule. The first falls within the 
range of the two bright bands A, = 4642 and 4688 of the Nova spectrum, and if faint, 
would be masked by them; while the second is probably not represented by the faint 
band 4747 to 4768 of the Nova spectrum lower down in the table. All the prominent 
lines of the nebule spectrum are present in that of the Nova, 3868 and 4364, in 
addition to the principal nebular lines and the hydrogen lines, and their wave-lengths 
agree within their probable errors. I have already said that the second line of Nova 
Persei could not be the hydrogen line 3970°2. The planetary spectrum is not decisive | 
on this point. All the hydrogen lines are bright, and the intensity of 3969 fits into 
their series, while its wave-length may be a t.m. in error. If it were the hydrogen 
line, the Nova spectrum after January 1902 could be reconciled with it. It is possible 
that a faint hydrogen band was superposed on the bright band »,=3967°0, and that 
after January 1902, when the band faded and the measurements became difficult and 
less accurate, its principal constituent was the band A,=3970. The only prominent 
band of the Nova spectrum which has no counterpart in the nebular spectrum belongs 
to wave-length 4725°3. : 
15. Variation of the Bands and of the Radiations i Intensity.—The degree of 
intensity » of the maximum of a band determines the intensity curve of the band. It 
alone requires to be discussed. From 1901 August 1 to October 6 the observed values 
of ~ agree with each other within their probable errors, and | have combined them to 
mean values. In this period the photo-plates Nos. 8 to 17 were all taken at the same 
angle of inclination. I have also combined the estimates made in three other periods, 
using in each period photo-plates taken at angles of 30° and 16°, and discarding those 
estimates which belong to bands out of focus. The results, which are corrected for 
the superposed bands, are tabulated in Table XVII. 
By means of the formule given in § 9 the relative changes in intensity of the radiations 
which produced the bands can be calculated. Leta radiation of intensity 7 in the focal plane 
of the spectrograph produce in time ¢ a degree u of blackness on a photographic plate | 
whose sensitiveness is s for the wave-length of this radiation, and I designate these | 
conditions by (2, s, w, t), and let a radiation 7, produce in the same time ¢ on the same | 
plate, for sensitiveness s, a degree m of blackness (%, So, @o, ¢), and for sensitiveness 3 a | 
degree u’y, (to, S, Mo, t). 
I define sensitiveness by st=constant for the same intensity of radiation and the | 
same degree of blackness. 7/i, is the quantity wanted. I apply formula (5) to (%, s, m, @) | 
and (45,584 pate 
