Page:Handbook of Meteorology.djvu/235

 to show the wet-line clearly the surface may be cleaned with alcohol, or—better—rubbed clean with 00 sandpaper.

Recording and Registering Gauges.—The registering and recording gauges are mainly of two classes—float-gauges, in which the increasing depth of water, by lifting a float balanced by a weight translates motion to a pen arm; and the tipping-bucket gauges, in which each tip of a full bucket moves an index hand.

The Marvin float gauge, used at many stations, is provided with a wind shield of the Nipher type, about 21 inches square. The drum carries a sheet ruled with lines nearly horizontal, but inclined so that they form a continuous spiral. These lines carry the record, one for each day of the week. Vertical lines divide the sheet into ten-minute spaces. The drum, driven by clockwork, makes one revolution in twenty-four hours. A screw thread of the required pitch causes the recording pen to follow the spaces between the spiral lines on the record sheet.

When rain begins to gather in the measuring-tube, the lifting of the float causes the rotation of the cam shaft and this imparts a lateral motion to the pen. The graph made by the pen