But the Institute is most justly celebrated for the researches on the motion and heights of clouds that have been carried on of late years under the guidance of Prof.  Hildebrandsson, with the assistance of Messrs. Ekholm and Hagstroem.

The first studies were on the motion of clouds round cyclones and anticyclones; but the results are now so well known that we need not do more than mention them here.

Latterly the far more difficult subjects of cloud heights and cloud velocities have been taken up, and as the methods employed and the results that have been obtained are both novel and important, we will describe what we saw there.

We should remark, in the first instance, that the motion of the higher atmosphere is far better studied by clouds than by observations on mountain tops, for on the latter the results are always more or less influenced by the local effect of the mountain in deflecting the wind and forcing it upward.

The instrument which they employ to measure the angles from which to deduce the height of the clouds is a peculiar form of altazimuth that was originally designed by Prof.  Mohn, of Christiania, for measuring the parallax of the aurora borealis.  It resembles an astronomical altazimuth, but instead of a telescope it carries an open tube without any lenses.  The portion corresponding to the object glass is formed by thin cross wires:  and that corresponding to the eye piece by a plate of brass, pierced in the center by a small circular hole an eighth of an inch in diameter.  The tube of the telescope is replaced by a lattice of brass work, so as to diminish, as far as possible, the resistance of the wind.  The vertical and horizontal circles are divided decimally, and this much facilitates the reduction of the readings.

The general appearance of the instrument is well shown in the figure, which is engraved from a photograph I took of Mr. Ekholm while actually engaged in talking through a telephone to M. Hagstroem as to what portion of a cloud should be observed.  The latticework tube, the cross wires in place of an object glass, and the vertical circle are very obvious, while the horizontal circle is so much end on that it can scarcely be recognized except by the tangent screw which is seen near the lower telephone.

Two such instruments are placed at the opposite extremities of a suitable base.  The new base at Upsala has a length of 4,272 feet; the old one was about half the length.  The result of the change has been that the mean error of a single determination of the highest clouds has been reduced from 9 to a little more than 3 per cent. of the actual height.  At the same time the difficulty of identifying a particular spot on a low cloud is considerably increased.  A wire is laid between the two ends of the base, and each observer is provided with two telephones—­one for speaking, the other for listening.  When an observation is to be taken, the conversation goes on