1884.] 
455 
Observations on Twilight. 
p. 240). His memoir, however, though inserted in a journal 
so constantly consulted by men of Science, appears to have 
passed unnoticed. Of this oversight the notices of the 
phenomena of last winter gave abundant proof. Had Prof, 
von Bezold’s paper been referred to the world would have 
seen that the displays in question were simply an intensifi- 
cation of the normal evening afterglow, and would not have 
rhapsodised anent electric discharges, the north light, &c. 
The author’s memoir would further have afforded a starting- 
point for a more complete study of the progress and the pe- 
culiar features of these phenomena. Our readers will not 
fail to remark the general agreement between Prof, von 
Bezold’s observations and those of Dr. Helmann. 
The former meteorologist describes the following pheno- 
mena as to be observed every morning and evening if clouds 
do not interfere : — 
A luminous segment appears on that side of the heavens 
where the sun is below the horizon ( i.e ., in the east in the 
morning, and in the west at eventide). It is separated from 
the higher parts of the sky by a peculiar light zone. Above 
this zone the heavens have a blue or purple colour, and 
below it are seen yellow, orange, and on the horizon even 
brownish red tones. 
At the opposite side of the heaven appears the dark seg- 
ment which is simply the ash-coloured shadow of the earth, 
which, as long as it is merely a few degrees above the hori- 
zon, contrasts sharply with that part of the sky still (or 
already) illuminated by the sun, — the so-called counter- 
dawn. 
There is also a faintly luminous circular disc of consider- 
able diameter (at the time of its greatest intensity), and of 
a rose- or pale purple-red colour. This the author speaks 
of as the “ purple light.” It appears above the luminous 
segment some time before sunrise or after sunset, in such a 
manner that the lower part of the disc appears to be con- 
cealed behind the luminous segment. The centre of the 
disc, in the evening twilight, goes down very rapidly, whilst 
at the same time its radius increases, so that at the last the 
boundary of the disc coalesces with that of the segment. 
The impression is as if the purple light was gliding down 
behind the illuminated segment. The purple light seems to 
play the part of an image of the sun, much magnified, but 
indistinct in its outlines. At the time of its greatest in- 
tensity the light generally increases very decidedly, so that 
objects which shortly after sunset were no longer distin- 
guishable are again recognised. This is especially the case 
