324 Mr Baxandall, On the Presence of certain Lines 
sharply defined lines in the spectrum of a Canis Majoris. From 
measures on these and the stellar lines under discussion and 
subsequent use of Hartmann’s interpolation formula the resulting 
wave-lengths for the three unknown lines measured are 
4384'7, 4428°4, 4434-3. 
Fowler’s wave-lengths for the three magnesium lines are 
438486, 4428°20, 4434:20. 
The differences here are no greater than one would expect, 
allowing for the weakness of the stellar lines. As a check on the | 
accuracy of the resulting wave-lengths, another line was measured | 
which was known to be identical with the laboratory line | 
Fe 440488. The deduced wave-length for this stellar line was 
4404-9. It is fairly certain, then, that the wave-lengths estimated 
for the weaker unknown stellar lines are correct to within + 0:2 
tenth-metres. | 
Fowler’s line 4384°86 falls in position between two well- 
authenticated lines in the a Canis Majoris spectrum. ‘The first 
is 4383°72, a very strong are and spark line of iron, the other 
4385°55, an enhanced iron line. In the stellar spectrum these 
two lines are nearly equal in intensity, and the line 43847 between 
them makes a close and almost equally spaced triplet with them, 
and there is no doubt about the separation of these lines in the 
best spectra of Sirius photographed at South Kensington with two 
Henry prisms of refracting angle 45° and aperture 6 inches. . 
Reference to the best spectra of this star in the Cambridge series 
of photographs used for radial-velocity work abundantly verifies 
the existence of the extra line. 
The line at wave-length 4384-7 was not recorded in the a Cygni 
spectrum in the publication previously referred to, but an examina- 
tion of the most recent Kensington photographs and the Cambridge 
radial-velocity plates leaves no doubt as to its occurrence in that 
spectrum. ‘Taking the three lines (4383'72, the extra line, and 
4385°55) as they occur in stellar spectra, the interval on the red_ 
side is a little smaller than the other and the wave-length of 
the middle line is 43847. There can be no doubt about the 
wave-lengths of the two outside lines, which are identical with 
the two solar lines 4883°72, 4385°55. If the wave-length recorded 
by Fowler for the magnesium line is correct, and if this line really _ 
does occur in the stellar spectrum, the resulting stellar triplet 
formed by this line and the iron and proto-iron lines should be 
spaced in the proportion of 11-4 to 6°9, the larger space being on 
the more refrangible side. As previously stated, the space on the 
violet side is greater than the other in the stellar spectrum, but 
certainly not in the required proportion, assuming that Fowler's 
wave-length is correct. 
