424 
feet, so that the Daphnias were far Jess directly illuminated by 
the scattered light. 
As in the preceding case, I placed by the side of it a similar 
cell containing water, and suspended them side by side over the 
water containing the Daphnias, and reversing the position after 
each experiment. The numbers were as follows :— 
Under the sul- Under the 
phate of quinine. water. 
SED aNs, ser) are Peano? LQ 47 
Repti Vl aa DY 43 
<a 12 48 
a Ir 49 
yy 20 40 
he) Ge Ye 3 18 42 
ss fe 20 40 
“et pay tear ate Be haan POG 45 
126 354 
Although the contrast in this latter series is not so great, still 
it is unmistakable. It seems to me, therefore, though I differ 
with great reluctance from so eminent an authority as M, Paul 
Bert, that the limits of vision of Daphnias do not, at the violet 
end of the spectrum, coincide with ours, but that the Daphnia, 
like the ant, is affected by the ultra-violet rays. 
GLACIERS AND GLACIAL PERIODS IN THEIR 
RELATIONS TO CLIMATE? 
New that the effects of glacial action, present and past, have 
been so well studied, the question as to causes deserves to 
be more attentively considered, and it seems that meteorologists 
must now take it in hand, having too long neglected it. A cur- 
sory glance on the present conditions of our globe shows us that 
cold alone will not produce permanent snow and glaciers when 
vapour of water is deficient. There are no permanent snow 
nor glaciers in the Verkhojansk Mountains in North-East 
Siberia, yet at the foot of them the mean annual temperature 
is below 4° F.,, and that of January below —56° F. The reason 
is that the snowfall is but small, and thus the snow is easily 
melted in summer. In New Zealand, on the contrary, owing 
to the enormous snowfall in the mountains, glaciers descend to 
about 700 feet above sea-level on the west side (lat. 43° S.). At 
this height the mean annual temperature must be about 50° F., 
and snowfall and frost are of rare occurrence, even in winter. 
The great importance of an abundant supply of vapour ad- 
mitted, and thus the necessity of surfaces covered by sea, what 
temperature of the surface of the seas is the most favourable to 
the production of glaciers? This depends certainly on the 
height above sea-level where the mevé is formed ; but so far as we 
consider lowlands and moderate heights, say below 6000 feet, the 
surface temperature of the water should not very much exceed 
the freezing point, otherwise the vapour evaporated from the 
sea and condensed on the surrounding lands will be rain, and 
not snow, thus contributing rather to melt the existing snow and 
not to form new snow-layers. For lowlands and very small 
elevations a temperature of the surrounding seas of about 32° F. 
is that which is most favourable to the. formation of snow, and 
if the last is falling in sufficient quantities to form permanent 
snow and glaciers. 
The deeyer and opener the seas are, the better, for such seas 
do not freeze entirely, as the winds and tides always break the 
ice which is already formed ; thus seas of that kind have, even 
in the midst of winter, a considerable open surface, which 
evaporates freely. Shallow seas surrounded by land can be 
entirely frozen in winter, and thus the ice and snow which cover 
them, considerably cooled by radiation and cold winds from the 
land, evaporate but very little, and are by far less favourable to 
a great precipitation of snow and ice. Thus the cold of winter 
in mediterranean seas is a condition very unfavourable to a 
great evaporation from their surface in the cold season, and to 
a heavy snowfall on the surrounding land. With the premises 
given above it will be easy to understand the difference in the 
extent of ice-sheets and glaciers, or their total absence in the 
different regions of our globe at the present time, as well as the 
probable causes of former glaciation. 
Abstracting for once from the polar regions of the southern 
hemisphere, of which we know but little, we see that in the 
higher latitudes of the southern hemisphere (40°-67°) the extent 
* Short analysis of my paper under the same title, published by the 
Zettschrift dex Geselischaft fir Erdkunde in 1881. 
NATURE 
of seas is much greater than in the same latitudes of the northern 
hemisphere. We know, further, that the seas of these latitudes 
receive considerable quantities of warm water from tropical seas, 
Now the south tropical seas do not exceed so much in extent 
the north tropical seas, then the seas between 40°-67° S. exceed 
the seas between 40°-67° N. If the latter were even to receive 
the same relative pro, ortion of warm water from the tropical 
seas of their own hemisphere than the southern seas of the same 
parallels, the thermal effect would be yet greater, on account of 
the limited extent of the seas between 40°-67° N. But the 
greater extension of the south-east trades and their existence 
even to the north of the equator pours a great quantity of the 
warm water of the southern tropical seas into the seas of the 
north temperate zone, thus giving probably an equal if nota 
superior quantity of warm water to seas of not half the extent. 
How much this must tend to raise the temperature of the seas 
between 40°-67° N. is easy to see. This explains why there is 
so little permanent snow in these northern latitudes in the 
proximity of the sea, notwithstanding the great precipitation 
existing there, and the greatest quantity of it falling in the 
colder part of the year. The temperature of the sea-surface is 
so high, that much more rain than snow falls even in winter. 
Let us take an example. The sea-surface between the south- 
west of England and the south of Ireland has a temperature of 
above 50° F. even in January. Supposing a saturated stratum 
of air to rise from these seas, it would have cooled down to 
about 384° F. at an elevation of 4000 feet, that is at the level 
of the highest peaks of the British Islands.1_ The resulting pre- 
cipitation will be rain and not snow. Thus a broad and swift 
atmospherical current from the south-west will give rain and not 
snow, even in the mountains of England and Scotland. As the 
south-west are the prevailing winds the absence of anything like 
permanent snow is easily understood. In Ncrway, where the 
surrounding seas are colder and the elevations greater, ‘per- 
manent snow and glaciers do exist. Greenland, which is sur- 
rounded by much colder seas, yet never entirely frozen, has an 
ice-sheet covering all the interior and forcing glaciers to the sea. 
The height of the ice-sheet is so great, and the sea so cold, that 
probably even in summer the precipitation is always snow in the 
interior. As the seas near Greenland are not warmer than 41° F. 
in summer, a saturated stratum of air rising from them will have 
a temperature of about 31°1° F. at a height of 3000 feet, that is, 
much below the level of the ice-sheet in the interior. : 
The seas between 40-67° S. have generally a much lower 
temperature than the northern seas of the same Jatitude (see, for 
example, the map in Wild’s ‘‘’Thalassa.’’) Thus their conditions 
are much more favourable to the production of snow at small 
elevations above the sea-level, and owing to the small difference 
of the temperature of winter and summer in so strictly oceanic 
climates, snow will fall even in summer. This explains why we 
find so great sheets of ice and glaciers descending to sea-level in 
all lands and islands south of 50° S. (the eastern part of South 
America, the Falkland and Auckland Islands excepted). 
As there is either a continent or a great cluster of high islands 
in high southern latitudes, and as the seas north of it give great 
quantities of moisture to be condensed to snow, a glaciation 
exceeding all that is known in the north hemisphere is the result, 
and the glaciers, descending to the sea, and their broken ends 
floating to the ocean as icebergs, they in their turn cool the sea 
water, and thus bring about temperatures favourable to the for- 
mation of snow. ‘Thus cause and effect react on each other, as 
is so often the case. We know besides that the southern seas do 
not freeze to a great extent, so that ice-fields, so frequent in higher 
northern latitudes, are far less common inthe south, the icebergs 
being the prevailing form of ice there. This shows us that there 
is, on the southern seas, always a great extent of open water, 
and thus an active evaporation. 
In the northern hemisphere, on the contrary, the colder seas 
are mostly shallow and surrounded by land, and thus frozen over 
to a great extent in winter (for example, the White and Kara 
Seas, the Sea of Okhotsk, Hudson’s Bay, the bays and straits 
between the archipelago of North America). Thus the evapora- 
tion is checked just at the time most favourable to a heavy 
snowfall. 
The continents of the northern hemisphere are too extensive, 
too little open to the influences of the sea and its moisture, to 
have extensive ice-sheets. ‘The example of mountains in North- 
East Siberia shows this very well. Similarly the great interior 
* On the Thermal Conditions of Rising and Descending Strata of Air. 
See Guldberg and Mohn’s ‘* Erudes sur les Mouvements de l’Atmosphére, 
\e a 
(March 2, 1882 
~ a eran anita alte 
ee ee 
