PHENOMENA RELATING TO THE SPECTRA OF HYDROGEN AND HELIUM. 
251 
in the ratio 2|-. This appears to imply that in the bulb, a definite transfer of the 
energy of emission takes place towards the lines of higher term number—-mainly in 
the present circumstances from the first to the second, but quite definitely also 
towards the third. If this be the correct interpretation, it has an obvious bearing on 
the anomalies met with in the spectra of nebulae, where AA4472 and 4G2G, with 
A4388 and, to a less extent, A4143 are abnormally bright in many cases in comparison 
with such lines as D :J . Examination of the other lines only serves to indicate the 
generality of this interpretation. The Sharp series of Helium contains, as its leading 
members, AA7065, 4713, 4121, corresponding to m — 3, 4, 5. Instead of the actual 
enhancement found in the later members of the Diffuse series, these are all reduced 
in the bulb, so that there is relatively less radiation sent out in the form of the Sharp 
series. But the nature of the reduction is very significant. For A7065 is reduced to 
about xm A4713 only to and A4121 only to fifi, so that the preferential transfer of 
the Sharp series energy is perhaps even more pronounced than that of the Diffuse 
series. The only line of the Principal series in the region we have examined is A3888, 
so that no conclusions can be drawn regarding it. 
The Diffuse series of Parhelium contains AA6678, 4388, 4144, corresponding to 
m — 3, 4, 5, 6 in the formula. This series exhibits the same phenomenon in a very 
pronounced manner. For in the bulb spectrum A6678 is reduced to fi, but A4922 
only to yfi, while the next member, A4388, is actually enhanced to lT, and the next, 
A4144, is even further enhanced to if. These are the other two lines mentioned 
already in connection with their enhancement in nebulae. 
An even more striking fact in the same connection occurs with the Sharp series of 
Parhelium. Its first visible member appears in our ordinary Helium spectrum, but is 
quite invisible in the wedge photograph from the bulb. This is the line A5047. But 
the next member. A4437, is visible in both, and is enhanced in the ratio 4'0 in the 
bulb. The next member, A4169, is visible in the ordinary spectrum of the bulb, 
though not in the wedge photograph, and is quite invisible with the ordinary 
discharge for the exposure given, even without the interposition of the wedge. This 
is a significant illustration of the effectiveness of the wedge method for determining 
variations incapable of detection by visual methods. The absence of this line in the 
ordinary spectrum, and its presence in the bulb under the same conditions, might 
have been noticed by visual or ordinary photographic methods. But without the 
present method of detecting comparatively small differences in order of intensity— 
as estimated by ordinary and very unsensitive methods—-it would have been 
impossible to interpret this phenomenon as part of a general effect extending 
throughout the spectrum, and an effect which must be fundamental to any theory of 
the origin of spectra. 
There remains the Principal series of Parhelium, whose members in the range 
examined are AA5015 and 3965. The same phenomenon is shown, for the former is 
reduced in the bulb to fifi, and the latter has the same intensity in both cases. 
