Page:Popular Science Monthly Volume 90.djvu/243

 Popular Science Monthly

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��addition to its regular stations (located mostly in important towns), about two hundred spe- cial snowfall stations in the mountains and foothills. The Bureau has also developed spe- cial forms of measuring appara- tus appropriate for such loca- tions.

The relation of the depth of snow to its water content is quite variable. It has been custo- mary, when more exact deter- minations were impracticable, to regard ten inches of snow as equivalent to one inch of rain- fall, but this assumption is only correct for snow of average density. In problems of water- supply the depth of snow is of no consequence in comparison with the water content, and the latter can be obtained either by melt- ing the snow before measure- ment, or by weighing the snow. The latter process is generally much simpler and is the one utilized in the type of gage used by the Weather Bureau at its mountain stations.

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��� �� ��The Latest Fashion in Snow- Measurers

The accompanying picture shows a gage recently designed by Professor Marvan, Chief of the Weather Bureau, suitable for measuring either rain or snow. At the top is seen a trumpet- shaped wind-shield, and in the middle the cylindrical can or collector into which the precipitation falls. The can rests upon a central support, which can be raised or lowered for placing or removing the collector. In making an observation, the can and its contents are removed and weighed by means of a spring balance, grad- uated to give the rainfall directly in inches and hundredths. The type of gage here shown is used for daily observations, but a modified form, with much enlarged collector, is used where observations can only be made at long intervals — in some cases only once a season. In this gage oil films are sometimes used to prevent evapo- ration.

Besides snow gages the Bureau uses snow stakes for measuring the depth of snow at various points around the station. The latest form of snow stake consists of a heavy

��The Marvin gage for measuring rain or snow. At the top is a trumpet-shaped wind-shield and in the middle a cylin- drical can, 'or collector into which the precipitation falls

��cypress stick of square section, painted white to minimize radiation elTects, and bearing on one of its faces a scale of enameled iron, graduated in inches. In the picture of the measuring stick on page 229 the num- bers attached to the scale represent tens of inches; I means 10 inches; 2, 20 inches; etc. These graduations can be read at a distance by means of binoculars or a telescope. The stakes are permanently installed in appro- priate locations.

Lastly, the ambitious attempt has been made in recent years to ascertain, early each spring, the total amount of water available in the form of snow over wild mountainous tracts adjacent to certain irrigation projects and remote from the fixed stations. "Snow surveys" of this sort were first carried out by Professor Church, of the University of Nevada, in the Sierra Nevada, and by Messrs. Thiessen and Alter, of the United States Weather Bureau, in the mountain- ous districts of Utah.

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