242 
NATURE 
[Fuly 15, 1886 
sometimes than at others. The further it deviates from 
it the greater becomes the difference between the length 
of winter and summer, and the difference may even 
amount to more than thirty days every year. The length 
of winter and summer varies therefore in the course of 
10,509 years, and the difference increases the more the 
earth’s orbit deviates from the circular. During the 
10,500 years in which the winter is longer than the summer 
there will be several thousand more winter days than 
summer ones, and in the second half-cycle there will be 
as many thousand less. Even at present, when the orbit 
deviates but little from the circular, the excess of winter 
or summer days for each half-cycle is more than 50,000, 
and when the deviation is greatest it amounts to nearly 
220,000 days, or some 600 years. 
As the cooling of the continents contributes to preserve 
the low atmospherical pressure over the oceans, and thus 
directs the prevailing winds and currents at sea, the winds 
thus directed, as, for instance, the south-west winds of 
the Atlantic, must be stronger in winter than in summer. 
And this is indeed the case. The weather conditions 
differ in summer and winter. Of course south-westerly 
winds blow predominantly in the North Atlantic and 
West Europe all the year, but they predominate more in 
the winter. According to Prof. Mohn, their force in the 
North Atlantic is about three times as great in the winter 
as inthe summer, and similar conditions prevail in the 
Pacific Ocean. In the southern temperate seas north- 
west winds, which correspond to south-west ones with us, 
are equally predominant when there is winter in that 
hemisphere. It will therefore be seen that the forces 
which promote the warm sea-currents in our latitude ave 
most active in the winter. And the same is the case in 
the Southern Hemisphere, so that it must be said that the 
winter favours these currents, whether it falls when the 
sun is nearest, as with us, or when it is most distant, as 
in the Southern Hemisphere. From Prof. Zéppritz’s 
studies of the currents it appears that the wind exercises 
an influence upon the strength of them even long after it 
has ceased to blow. The action of the winds is summed 
up through centuries, avd the total recorded in the sea- 
currents. 
As we know that the wind conditions vary at different 
seasons, and that the effect of the wind does not cease 
as soon as it is discontinued, but leaves traces in the sea- 
currents for a long time after ; so that, in fact, the strength 
of the current is dependent on the average force of the 
wind during last great ages—it can hardly be a matter of 
indifference whether these thousands of days fall as a 
surplus to winter or summer in the 10,500 yearly half-cycle. 
When they fall in the winter, the south-west winds must 
be more predominant than others ; and, correspondingly, 
when they fall to the summer, weaker. It seems, therefore, 
reasonable thatthe currents must increase or decrease as the 
equinoctial line moves round. When the winter falls in 
aphelion our warm currents will increase, and when the 
reverse is the case they will decrease. We should, there- 
fore, now in the Northern Atlantic have a weaker current, 
and in North-Western Europe less rain and a greater 
difference between winter and summer heat, aud ¢his zs 
exactly what the theory demands. 
In regions with different weather conditions the case 
will be different. For instance, in the eastern part of 
North America north-west winds are more predominant 
in the winterand south-west ones in the summer. Winter, 
in aphelion, would here increase the north-west wind, and 
one might conclude that these parts under such con- 
ditions would perhaps thereby obtain a more severe 
climate, so that it seems evident that variations in the 
climate will not simultaneously move in the same direc- 
tion everywhere in the Northern (or Southern) Hemisphere. 
From calculations we have elsewhere demonstrated 
that the varying length of the season alone during the 
precession of the equinoxes will cause an increase or 
decrease in the force of the current of several per cent. 
of the total. And these figures are doubtless below the 
true ones, but space does not here permit of develop- 
ing them. We may, therefore, with a high amount of 
probability conclude that the precession of the equinoxes 
causes periodical variations of the climate which are 
great enough to explain all the facts on which the 
theory for these periodical variations ts based. 
But the eccentricity of the earth’s orbit changes so 
rapidly that in two consecutive half-cycles it is not as a 
rule the same. Therefore variations in the strength 
of sea-currents, and consequently also those in the 
climate in one half-cycle will not be quite balanced in the 
next, and it might even be possible that greater and more 
lasting variations of the climate might be caused by the ~ 
same agencies. A. BLYTT 
The University, Christiania 
VEGETABLE PRODUCTS AT THE COLONIAL 
AND INDIAN EXHIBITION 
IN passing through the various courts of the Colonial 
and Indian Exhibition the prevailing natural resources 
of each colony are apparent even to the most unobservant, 
for while the riches of some countries are to be found 
chiefly in their vegetable products, the wealth of another 
is in its mineral resources, and of another in its animals. 
Regarding the vegetable products, as might be sup- 
posed, some of the most interesting objects from a scien- 
tific point of view are those which have the least attraction 
for the general public, such, for instance, as the large and 
varied collection from the Straits Settlements, or the 
interesting exhibits from British North Borneo. Amongst 
the exhibits from the former possessions are various 
samples of damar, the botanical origin of which is but 
imperfectly known ; thus, for instance, are specimens of 
damar sesa, a fossil resin from Larut, Perak, damar meta 
kuching, or cat’s-eye damar, damar renkong, and others. 
Another fossil resin new to us is called incense or gum 
Benjamin. Under the name of buah saga are shown 
some seeds of an Adenanthera, probably those of A. 
pavonina, a seed of which is the unit in the Malay 
jeweller’s weight, equal to 4°33 grains troy. The seeds 
are also eaten by the natives. The tree is found in India, 
China, and the Philippines. In India the wood, which is 
of a red colour, hard, and close-grained, is known as red 
sandal-wood, and is used as a red dye, as well as for 
cabinet-making and building purposes. On account of 
their bright red colour the seeds are used as necklaces. 
Naturally in countries where the bamboo is abundant we 
should expect to find numerous illustrations of its uses, 
and various articles of domestic utility, as well as for other 
applications besides that of ornament, are shown, some of. 
which are very ingenious, such as a trap called grogoh, 
used for catching river fish ; it is somewhat of the shape 
of an eel-pot, and the body of the trap is made of a single 
piece of bamboo-stem of about 2 inches diameter, and 
from 14 to 18 inches Jong. It is split longitudinally for 
the greater part of its length into fine strips, these are 
distended to a wide mouth at the top some 6 or 8 inches. 
diameter, tapering to the point from which they spring, 
where they form the natural stem. By the addition of 
other fine strips of bamboo fastened round at short in- 
tervals a complete funnel-shaped basket or eel-pot is 
made, the lower or tubular end of which is formed by the 
hollow bamboo-stem. The ready way in which the natives 
adapt natural productions is seen in a very simple spinning- 
top, which is composed of a flattened acorn of the type of 
Quercus placentaria, through the centre of which a piece 
of wood is driven. In this division also are some very 
varied sets of betel-chewing appliances as used by the 
Malays, including the scissor-like implements used for 
cutting the betel-nuts ; many of these sets are in deftly- 
worked brass, while others are in more costly metals. 
Pir He yee, 
