Finally, let us look for a moment at two sketches that I have made to give a graphic and I hope not incorrect idea of the cloud formation and the internal structure of a hurricane. In both sketches the vertical scale is of course greatly exaggerated. The first illustrates particularly the great cloud bank (with the "bull's eye," or clear central space, shown in cross-section); the storm-wave or general elevation of the surface of the ocean caused by the spirally in-blowing winds and low barometric pressure (the cause, oftentimes, of fearful floods along low-lying coasts); and the probable, or possible, circulation of the upper atmosphere over the whirl, together with the direct and reflected rays of a vertical sun as they pour into the central calm. The second sketch is to aid a clear mental conception of the actual motions of the particles of air as they flow inward below, whirl about the central core and flow outward above; this may help to free the mind from an erroneous idea that may be suggested by thinking of or seeing the enormous, piled-up, apparently stationary mass that constitutes the barra, or cloud-bank of the hurricane, but which is really only the stationary and visible locus where the conditions are such that the whirling, rushing masses of humid atmosphere condense their tons of aqueous vapor and leave it, as they pass upward and outward. It is analogous to the cloud-cap, or banner, that hangs stationary over a lofty mountain peak, although if you visit the peak you may there find a living gale of wind.
| Sketch, in cross-section, to illustrate the cloud-formation, storm-wave, etc., in a hurricane. The dotted lines represent the probable circulation of the upper atmosphere. |
| Sketch, in perspective, to illustrate graphically the lower-atmosphere-wind-circulation in a hurricane. The inward spiral at the base is the surface wind. |
In both of these sketches my object has been to try to convey an idea of the marked individuality, symmetry, and intensity of a tropic cyclone, and its grasp upon and intimate connection with the ocean, which it joins to the upper atmosphere by a huge, hollow trunk, with widely extended roots and spreading branches,—no doubt an enormous and effective conductor of atmospheric electricity, too, whose power is quickly shattered and destroyed by contact with the land; the notable absence of thunder (illustrated by the report of the "Victoria," quoted above) is of interest in this connection. If I have succeeded in this, and thereby given a clearer idea to the casual reader or suggested a fertile train of thought to any physicist, I shall feel more than repaid for the effort.
I have thus attempted little more than to touch upon the practical side of this great question, and this in a popular way, to induce my readers to follow me to the end. The many other interesting questions that might be raised and discussed must here be left untouched. Our efforts in the Hydrographic Office must be primarily to help the navigator, and only secondarily to try to collect and publish facts for the scientist to study at his leisure. The causes of these terrific storms are of interest to us as they may help us to predict their coming, rather than for the proof of any theory, or the gratification of any pet idea. And if Science will but improve the Law of Storms, as practical men use it for the guidance of their vessels and the safety of the lives and cargoes intrusted to their care, it will be one more welcome proof that theory and practice go hand in hand.
THE IRRIGATION PROBLEM IN MONTANA.
BY H. M. WILSON.
The development of the irrigation resources of a region under the supervision of the Government, requires study of the social and political conditions and of the industrial occupations of its inhabitants.
The determination of the best plan for the utilization of its waters and agricultural lands is a problem in irrigation engineering. The solution of this problem calls for an intimate knowledge not only of the best methods of construction, but also of the values of its various agricultural products and soils; for a knowledge of its rainfall, evaporation, and steam volumes and of the duty of water. It further requires such an understanding of the topography of the region as will enable the engineer to determine the area of the catchment basin of each stream, and to intelligently select sites for the construction of canals and storage reservoirs and to determine from what source of water supply each district may be best irrigated.