16 ANNIVERSARY ADDRESS. | 
marked distinctness. The upshot was that the weather changed 
completely about midnight ; rain set in, and continued for several 
days. 
With this spectroscope I have frequently examined the red 
glows which at intervals for nearly eight months have afforded 
such grand and puzzling displays of nocturnal splendour. Even 
yet they occasionally irradiate the evening and morning skies, 
though shorn of their earlier glory. 
The spectrum of the red light appears to be almost identical 
with that of the ordinary red clouds which often attend the 
setting sun. I exhibit two diagrams, in which I have attempted 
to represent what I have seen with this spectroscope—first, when 
directed to a glowing sunset in the tropics, and, second, when 
directed to the red after-glow here. The two are substantially 
the same, the chief difference being on the red side of D, where in 
the case of the tropical sunset there is a distinct line, which I 
understand to be the special “‘rain-band,” and in the after-glow this 
line disappears in the general shading that stretches from D half- 
way to “a.” The line a between D and C is broader and denser 
in the after-glow than in the sunset. So far the evidence might be 
taken as showing that both phenomena arise from the same cause, 
namely, water in some form in the atmosphere ; but the spectro- 
scope is by no means able to settle this difficult question ; it 
analyses the light that comes to us, but does not identify the 
agency that decomposes and reflects the light. It is possible that 
the polarisation of the reflected rays might throw some light on 
the nature of the reflecting substance, but probably the light is 
too faint for such an observation ; at all events I have not seen 
any record of observations of this kind. You must all have 
watched and admired these strange and beautiful evening and 
morning displays, for which, by the way, we are in want of a 
good 
distinctive appellation, and no doubt you are all aware of 
the various explanations that have been put forth; but let me 
remind you of the leading features of the phenomenon. I have 
not myself been favourably situated for good observations, and I 
