NATURE 
[FepRuARY 4, 1897 
photographed. Our first illustration (Fig. 1) shows the ap- 
pearance of a cumulus.cloud as seen from the top of the 
Santis Mount at a height of 2500m. At this elevation a 
yellow glass placed in front of the lens is all the protection 
needed. The other picture (Fig. 2) shows that excellent 
results can be obtained at the sea-level with proper chem- 
ical treatment of the negative. These pictures were 
taken by Prof. Riggenbach, who kindly permits their re- 
production, and both appeal to us by their evident fidelity. 
But it must.not for a. moment 
be supposed that the objectsought 
is to secure pretty pictures, or 
even accurate pictures. In clouds 
we have) portions of the atmo- 
sphere which, from natural causes, 
have become temporarily visible, 
and as clouds exist at practically 
all heights above the surface, 
their study must reveal to us 
something of the behaviour of 
the atmosphere at otherwise inac- 
cessible points. Wind and cur- 
rents of the atmosphere, to say 
nothing of the vertical displace- 
ment of large masses of the air, 
must betray themselves by the 
motion of the clouds, if the cloud 
movements are interpreted cor- 
rectly ; and the connection be- 
tween wind and “ weather” is so 
intimate, that the possibility of 
predicting the one depends in a 
large measure upon our know- 
ledge of the other. The definite 
knowledge of the height of a 
cloud, and the means of accurately 
determining its distance becomes, 
therefore, a problem of the highest 
importance in meteorology, and 
it is one in which, fortunately, 
photography can render efficient 
assistance. If two simultaneous 
instantaneous photographs of the 
same cloud be secured at stations, 
distant possibly half a mile apart 
from each other, the height of 
the cloud can be determined by 
trigonometry. This process has 
been carried out systematically 
at various observatories. Two 
observers, a suitable distance 
apart, and in connection with 
each other by telephone, select a 
cloud by arrangement to which 
each points a camera, and the 
simultaneous exposure is effected 
by one of the operators releasing 
the shutters of both cameras at 
the same instant. Considerable 
impetus has been given to in- 
quiries of this nature, not only 
by the possibility of greater ac- 
curacy being secured to the 
photographs when improved 
methods have been employed, 
but by the action of the International Meteorological 
Congress, who, mainly at the instance of M. Hilde- 
brandsson, have arranged a scheme by which observers 
in all countries are invited to take part in a com- 
mon investigation, which has for its aim the deter- 
mination of the altitudes and the motions of different 
i 1 M. Plumandon, of the Puy de Déme Observatory, has also sent us 
some excellent specimens of his work, but the photcgraphs arrived too late 
to be reproduced. 
NO. 1423, VOL. 55] 
kinds of cloud. Vheodolites can also be used advan- 
tageously in this work. | This scheme, which was origin- 
ally contemplated to be in force for one year from May 
1896, will soon be completed, and will add materially to 
our knowledge of the motions of the clouds, and, by 
inference, of the motion of the atmosphere. The obsery- 
ation of the behaviour of a kite, when at a considerable 
elevation it plays in some measure the part of a cloud, 
can be made, in skilful hands, to reveal the direction of 
Fic. 2.—Clouds, photographed at low-level station 
atmospheric currents at generally inaccessible heights. 
This method, which is being actively prosecuted under 
the auspices of the Weather Meteorological Bureau of 
America, has the advantage that the height of the kite 
is always approximately known, and is free from eddies 
and currents likely to be produced by irregularities on 
the earth’s surface. Moreover, if the object of cloud 
observation be not so much the methods of formation as 
the study of air currents, kite-flying is likely to afford on 
