288 PROFESSOR L. BECKER ON 
17. Last Visual Observation of the Spectrum.—On March 3 1903 I inspected the 
spectrum of Nova Persei in the focal plane of the spectrograph without using an eye- 
piece, a method which I usually employed prior to the exposure, to make sure that the 
proper star had been set on the slit. I saw only one bright spot in the whole range of 
the spectrum which coincided with the air band at 5004. Several times I gained the 
impression that there was a faint spot near the place of the magnesium line 4481. The 
comparison was made in this way, that when the eye had been fixed on the spot the 
spark was switched on for an instant. 
18. Curious relation between ~* of Four Prominent Lines.—The wave-lengths of the 
zeros of the brightest bands are 3869, 3967, 4364 and 5007. ‘The oscillation frequencies 
of the first, third, and fourth zeros almost form an arithmetic series, which, continued 
to the less refrangible side, gives the wave-length of the helium line D,, a line which 
was measured by others in the spectrum of the new star, and also belongs to the nebular 
spectrum. In the following table I give the wave-length of the helium line, Keeler’s 
determination of the nebular line, and my determination of the other two lines, reduced 
to the two nebular lines as standards. 
The formula 
A-! = 17014:2 4 2957-6n—5:5n2, n= 0,1, 2,3 
determines » as entered in the last column. The agreement is perfect. Should this 
be merely a casual coincidence ? 
A | = Vacuum. Difference. Calculated a. 
3869°2 25837°8 3869°2 
| 2931-0 
4364°3 | 22906'8 4364°3 
| 2940°5 
5007°05 | 19966°3 500705 
2952-1 os 
5875°87 | 17014°2 587587 
19. Similarity of the Structure of the Bands in March-April 1901 and after August 
1901.—I add da,,= +1.1 t.m. to a, of Table XIV., which reduces them to the same zero 
as was employed for the March-April bands. Both bands are given in Table XVIII, and 
also on Plate II. I include the second minimum of the March-April band, though it 
rests on only two single measurements in two bands, because it seems to fill up a gap in 
the order of the minima. The extent of the maximum and the position of the minima 
agree with each other. There is only this difference, that while the March-April band 
declines to nothing from a)= —12 to —73 t.m., and from +13 to +56 t.m., the later 
bands fade abruptly on 6 t.m. Between April and August the ends of the bands have 
therefore decreased at a greater rate than the central maximum portion. I repeat again 
that from August 1901 to January 1902 no change took place in the structure, and 
that the extent of the maximum remained unaltered during 1902. It appears that the 
spectrum converges towards a nebular spectrum, in which each line is broadened 27 t.m. 
