IIIF Color HighRes
National Institute of Informatics - Digital Silk Road Project
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| IIIF Color HighRes |
| Scientific Results of a Journey in Central Asia, 1899-1902 : vol.2 |
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| Dune- and wave-movements |
Citation Information
420 THE CENTRAI. ASIAN DESERTS, SAND-DUNES, AND SANDS.
most may at the next moment have the whole of the drop to which it belongs resting upon it. A similar phenomenon may often be observed in Northern Tibet, where in summer some of the smaller eroded watercourses carry water in the afternoon only, because it is not until then that the water is able to get down from the regions in which the snow is melting. You hear the water coming roaring down the dry watercourse, you see its advancing front rolling on like a muddy, turbid
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eagre, and it is quite easy to see that in its front a rolling movement is taking place, in such sort that the water-particles which recently rode at the top are now underneath. There is a third, and even more important, instance to which I shall revert presently; but before I do so, I wish to direct attention to the different paths described by a point (I) on the periphery of a circular cylinder, which is rolled by hand along a tabletop — we have then the trochoidal path which we find again in the wave-movement of a fluid; (2) in an elastic cylinder, which is rolled along the table in the same
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~`Î ----
__.._~ ................__.._...._...__.._.wsa~~s_•~~
~--=-- -- =•___- ' - _
Fig. 184.
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