THE SPECTRUM OF NOVA PERSEI AND THE STRUCTURE OF ITS BANDS. 283 
majority of the minima detected on the plates of 1902 belongs to the first two bands, 
which at first were the brightest of the spectrum, and then second in brightness only to 
the 5006-band. They are present on each of the three photo-plates on which they were 
in focus, plates Nos. 21, 24, 26, 1902 January to November. During this time there 
is also no change in the extent and the position of the maximum of the bands. The 
evidence therefore points to the conclusion that from August 1 1901 to the end of 1902 
the structure of the bands remained unchanged. 
Taste XV.— Zable showing the Number of Photo-Plates on which the Mimma 
have been measured, and the Periods to which they belong. 
x Minimum 1. Minimum 2. Minimum 3. 
of 3 z 3 
Pande, 3 Period. ie Period. = Period, 
i=] 5 =] 
A A A 
| 3869°5 6 |1901 Oct. to 1902 Mar.| 4 |1901 Oct. to 1902, Mar.| 4 |1901 Oct. to 1902 Nov. 
39680 4 | Oct. to Jan. 6 Oct. to Nov.| 4 Oct. to Jan. 
4103°4 te | Aug. to Nov.| 6 Aug. to 1903 Jan. | 5 Aug. to May 
4341-0 8 Aug. to 1901 Nov.| 7 Aug. to 1902 Nov.| 5 Aug. to 1901 Nov. 
| 43645 | 130 Aug. to 1902 Jan. | 9 Aug. to 1901 Nov.| 7 Aug. to Nov. 
| 4612-6 1 Sept. 4. | 3 Aug. to Nov.| 1 Aug. 15. 
4642°0 4 Aug. to 1901 Sept., 1 Aug. 26. i 
4687°8 9 Aug. to INOW: |e 8 Aug. to Nov. 
47156 | 11 Aug. to INiov:, | 2... es 
4726°1 8 Aug. to Nov. | 5 Aug. to Nov.| 3 Oct. to 1902 Mar. 
4862°8 f Aug. to Oct. 4 2 Aug. 21, Sept. 4. one 
4959-4 4° Aug. | 1 Nov. 13. oa 
5007°2 8 Aug. to 1903 Jan. | 3 Aug. to 1901 Sept. 1 Sept. 4. 
A fourth minimum was measured twice in band X,,= 4364.5 on 1901, August 21 and 26. 
14. Identification of the Bunds.—The wave-lengths ,, of the zeros of the principal 
bands are compiled in the first column of Table XVI. Five of these can with certainty 
be identified as the hydrogen lines H,, H,, H;, and the two principal nebular lines. A,, 
is the wave-length of an arbitrary zero of the band, viz., approximately the mean of 
the wave-lengths of the three minima. I change the zero and make it coincide with 
the wave-length A, of the line to which the band would be reduced under ordinary 
conditions. Let [s] be the mean of the corrections for the orbital motion of the earth 
on the days on which the photographs were taken, then 
r r 
A=AX — =X — 
0+ Mops =m + LI + Am gso9 
(13) Sapa als sess Pie) ) 
Xp =A — A 
4500 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART II. (NO. 10). 43 
8am +[s] 
