Oct. 29. 1885} 
and “wet bulbs by Glaisher’s tables had been compared with 
those given by a new form of hygrometer designed by Prof. 
Chrystal of Edinburgh University. As regards Mr. Aitken’s 
screen, in some a fan was introduced in order to secure a proper 
and uniform circulation of air for the thermometers in all 
weathers ; others were simply sunshades ; cne consisted of two 
thermometers, one of which was partially blackened; and 
another of a thermometer having its bulb inclosed in a tight- 
fitting silver sheath, highly polished. The construction of Prof. 
Chrystal’s hygrometer was explained and a brief account given 
of the results either already arrived at or suggested during the 
investigation, and it was intimated the inquiry was to be resumed 
at the Ben Nevis Observatory during August and September. 
At this Observatory, the climate of which offers unique facilities 
for the prosecution of such inquiries, an instrument of novel 
construction would be added, which had been designed by Prof. 
Tait for hygrometric research. Prof. Ewing, of Dundee, then 
described the arrangements which had been made for commenc- 
ing the proposed earthquake observations on Ben Nevis this 
summer. The investigation was to include earthquakes proper ; 
earth movements of so very delicate a kind as to be totally in- 
distinguishable without some form of instrumental assistance, 
which are conveniently called earth tremors ; and there were 
what might be named changes of the vertical, or those tiltings 
which the earth’s surface seemed to be constantly undergoing. 
The different seismometers to be employed at the Observatory 
were then described, and in illustration some of the more 
striking peculiarities of the earthquakes of Japan were re- 
ferred to. 
PROF. KIESSLINGS INVESTIGATIONS INTO 
GHE ‘ORIGIN OF THE LATE SUNSET 
GLOWS? 
‘THE interesting and important experimental demonstrations 
lately made by Prof. Kiessling of Hamburg to illustrate 
the artificial formation of all manner of sunset effects are prob- 
ably well known to meteorologists in general. The September 
number of Das Mette contains a valuable series of com- 
parisons tending to show that the conditions under which 
artificial glows were produced have actually existed whenever 
the remarkable sunset effects have made themselves prominent. 
The following abstract may prove of interest to those who do 
not receive the paper itself. 
With regard to the ‘after-glow,” or re-illumination, he sug- 
gests two explanations as possible:—(a) Simple reflection of 
the refracted rays essential to the formation of the ordinary sun- 
set-glow (the frst glow); or (0) direct diffraction by a second 
homogeneous haze at much greater elevation. He considers, 
however, that the calculated heights of the latter place it out of 
the question. To the former there are only two important 
objections, the chief one being the slight polarisation, so far 
as the very scanty records indicate. The observations are, how- 
ever, exceedingly deficient. Still, Prof. Kiessling has to allow 
that they do not tell in favour of the proposed explanation. 
The other difficulty is the Aosttion of the glow. It presupposes 
a mirror-like surface, parallel to the earth, with the intermediate 
space unusually transparent, conditions at first sizht very im- 
probable at the altitudes under consideration. But Prof. 
Kiessling’s own experiments, detailed at the end of his paper on 
“Die Dammerungserscheinungen im Jahre 1883,” have shown 
the possibility. In these he obtained results most remarkably 
similar to those requiring explanation, and by methods re- 
producing in a striking manner the conditions considered 
actually to exist in the atmosphere. 
A warm, moist stratum of air being produced in contact with 
a cold stratum the resulting haze along the contact surface 
formed the site of diffraction phenomena, approaching those 
actually observed in ordinary brilliant sunsets according to the 
fineness of the haze particles, and also reflections reproducing the 
“ after-glow.” 
The almost constant saturation of the cold upper strata in 
winter is indicated by observations at high-level stations and the 
persistent upper haze. Let a warm [cyclonic] current come 
beneath such a layer, then the fine haze at the surface of contact 
will have beneath it the peculiarly transparent atmosphere common 
to such conditions and requisite for the transmission of the result- 
1 Ueber die Entstehung des zweiten Purpurlichtes und die Abhangigkeit 
der Dammerungsfarben von Druck, Temperatur, und Feuchtigkeit der Luft 
Das Wetter, vol. ii. No. 9, p- 161. 
NATURE 
637 
ing diffraction (and reflection) phenomena. This should be found 
to exist in a// brilliant sunsets, Prof. Kiessling stating the 
following law :—Ax intense purple glow, visible over a consider- 
ablearea, may occur when, in close proximity beneath a lofty and 
highly-attenuated haze, there ts formed an extensive stratum of air 
at considerably higher temperature. 
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Although we cannot ever expect direct observations of tempe- 
rature at the common surface producing the sunset glows, yet, 
as Prof. Kiessling shows, if we can prove that the warm under- 
current always accompanies sunset glows, the proof is practically 
complete. Such indications may be expected during the colder 
seasons in the form of abnormal vertical distribution of tempera~ 
