sists of a sinuous line which curves back and forth across the day line. A complete revolution of the cam records half an inch of rain. The faster the precipitation, the sharper are the curves.
The Marvin gauge possesses several distinct advantages. Recording begins within a very few minutes after precipitation has commenced—a merit not possessed by tipping-bucket gauges; it likewise records the cessation of rainfall rather more promptly. A very desirable feature is the fact that it also records the rate of rainfall, a matter of great importance. In many instances the total of precipitation is of minor consequence, while the rate per unit of time must determine the discharging capacity of sewers and other run-off systems. The Marvin gauge is not fool-proof, but this detail applies also to other recording instruments.
The tipping-bucket gauge is chiefly used for recording rainfall. The drip from the funnel falls into one or the other of two scoop-shaped buckets placed back to back mounted on trunnion bearings. When 0.01 inch of rain has collected in a bucket the weight causes it to tip, spilling the water into a container and moving a pointer one division on a dial. The tipping of the full bucket swings the empty bucket into a position where it catches the drip.
Where a Friez triple recorder is used the pen which ordinarily records sunshine is also used to record rainfall. This it does with little or no confusion of records, because precipitation rarely occurs in appreciable amount while the sun is shining.
Tipping-bucket rain gauges are constructed so close to exactness of measurement that, when placed side by side with the standard gauges, the difference between the measurements of the two is not much greater than that of two gauges of the same type side by side.
Although the tipping-bucket rain gauges are simple in construction, various conditions may occur that result in erroneous recording. The bucket may rebound on emptying itself, in which case two registrations instead of one are made. With the Friez gauge this will appear as a mark of double length on the record. With the dial gauges, which register but do not record graphically, double registration cannot be discovered except by close watching. It may be suspected, when the catchment of the registering gauge runs uniformly greater than that of the
