Littell's Living Age/Volume 135/Issue 1748/The Motion of "Cirrus" Clouds
THE MOTION OF "CIRRUS" CLOUDS.
The researches of Mr. Clement Ley into this subject are well known, and now we have to notice the appearance of a most important work by Prof. Hildebrandsson, of Upsala, entitled "Atlas des Mouvements supérieurs de l’Atmosphère," which is published at the expense of the Swedish government, and is copiously illustrated by fifty-two charts. In the discussion the author fairly says that meteorology is still in the first stage of its development as a science, and that what is at present necessary is to determine what are the real facts of air movement before beginning to theorize about them. The paper accordingly contains a most careful digest of the present state of our knowledge of the motion of the air in cyclones and anticyclones, as given by the best recent authorities, and then proceeds to treat the materials for the study of the motions of upper clouds furnished by the observations collected from the various volunteer stations established in different parts of Europe, which are, however, very scanty compared with what is really requisite. He summarizes the final outcome of his labors as follows: — Around a barometrical minimum the air moves along the earth's surface in a spiral path towards the centre, in the direction opposite to watch-hands. At the centre it rises and moves further and further away from the axis the more it ascends. In the upper strata of the atmosphere the air flows away from the region of minimum pressure, and collects itself in a uniform layer above the district of maximum pressure, where it gradually descends to the surface of the ground in order to flow away from the region of highest barometrical readings. These statements are based on the evidence afforded by the charts, and, speaking generally, we find some eight or ten cirrus observations on each chart. The final dictum, however, merits great attention, as it comes from a most painstaking investigator, but it is needless to say that it indicates the necessity of increased efforts to collect observations of cirrus clouds.