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0:.n254 -25- PRECIPITATION Types of gages By far the greater part of the published records of precipitation have been derived from the non-recording 8-inch precipitation can with funnel and measuring tube which has been the standard gage for more than a century. In such gages the catch of precipitation is measured periodi- cally by an observer, commonly once each day. Daily, monthly, and yearly amounts of precipitation so measured are published currently by the Weather Bureau for about 13,000 stations, in "Climatological Data for the United States." Precipitation amounts that are measured less frequently than once a day are published separately. Most such records are from non-recording storage gages in remote areas. Examples are the standpipe, "Sacramento," and extended 8-inch cans which have capacities for storing la~ge amounts of precipitation. Oil and anti-freeze solution generally are placed in these gages to retard evaporation and prevent freezing. Recording gages are installed at first-order stations of the Weather Bureau and at other locations to measure precipitation rates by hourly or shorter intervals (3,500 stations). These gages generally embody an 8-inch-diameter funnel to catch the precipitation and a clock-driven chart on which the catch is recorded. Three types of recording gages are in common use. In two of the three the catch passes to a receiver, from which the recording mechanism is actuated by the increasing weight or the rising water level. In the third type, the catch passes to a "tipping bucket" whose action marks a tick on the chart for each 0.01 inch of precipitation (or by some larger increment). At Weather Bureau stations, recording precipitation gages commonly are of the weighing type. Where both a recording and a non-recording gage are installed, the official amounts of precipitation are those indicated by the recording gage. Records published by the Weather Bureau from its recording precipi- tation gages show hourly, daily, monthly, and yearly amounts. So pub- lished, the amounts of hourly precipitation are those for clock hours; they should not be construed as instantaneous rates of precipitation, which may be several-fold greater and which can be derived from the recorder charts. Exposure and spacing of gages The, amount of precipitation occurring at any given point is con- trolled primarily by meteorological conditions, by the location in relation to storm paths, and by large-scale physiographic features such as the oceans, plains, and mountain ranges. In turn, the percentage of