80 PROFESSOR J. N. LOCKYER ON THE PHOTOGRAPHIC 
5 
Some of the more important variations are indicated in fig. 3. The stars, the spectra 
of which are registered on the plate, will be readily identified by a comparison of 
figs. 1 and 8, the spectra of the trapezium stars being shown at the bottom of the 
diagram, and that of the star G. P. Bonp 685 (HERSCHEL’s €) at the top. 
It will be seen, for example, that the line near ) 495 falls off in intensity about 
the middle of its length, while the lines of hydrogen show no such reduction in the 
same part of the nebula. If we first consider the phenomena, in the neighbourhood 
of the star G. P. Bonn 685 (HERSCHEL’S e), near the trapezium, it will be seen 
that here the lines 4471 and 4495 are most intense. In this region there is also a 
distortion of the two lines at 4471 and 4495; they are sharply bent towards the 
red end of the spectrum, whilst the other lines remain straight. Unfortunately, the 
spectrum of this star is only shown on the photograph of February 10, and, in the 
absence of other photographs, it is possible that the displacement of the two lines in 
question may be due to a distortion of the gelatine film. The displacement of the 
lines, if real, would indicate a velocity of about 200 miles per second, in the line of 
sight. Both lines are brightest where they are most disturbed. 

Fig. 3. Diagram showing the principal lines in the photograph of the spectrum of the Orion nebula, 
February 10, 1890, with their relative intensities. The spectra of the stars in the trapezium are 
shown at the bottom of the diagram, while that at the top is the spectrum of the star Bonp 685. 
It will be seen, also, that where the lines of the nebula cross the continuous 
spectrum of the star, they are considerably broadened. This is seen in all the 
principal lines from d 378 to \ 495. 
Where the chief line (500) crosses the spectrum of the star, there is a decided 
indication of a reversal. As it approaches the star, the line bifureates and reunites 
on the other side, leaving a short dark line where it crosses the spectrum of the star, 
as shown in fig. 3. This reversal is not seen in the case of the hydrogen lines, but if 
it be subsequently confirmed in the case of 500, it will be an indication that some of 
the nebulous matter lies in front of the star in question (Bonp 685; HERSCHEL e). 
