) The second
requisite is a piece of stout glass tubing having an internal diameter not
more than one-quarter that of the receiver This is to serve as measuring
glass.
[Illustration: FIG. 152.--Section of homemade rain-gauge.]
The success of the gauge depends entirely upon ascertaining accurately how
much of the tube will be filled by a column of water 1 inch deep and having
the same area as the receiver. This is easily determined as follows:--If a
tin is to be used as receiver, make the bottom and side joints watertight
with solder; if a tube, square off one end and solder a flat metal to it
temporarily. The receptacle is placed on a perfectly level base, and water
is poured in until it reaches exactly to a mark made 4 inches from the end
of a fine wire held perpendicularly. Now cork one end of the tube and pour
in the water, being careful not to spill any, emptying and filling again if
necessary. This will give you the number of tube inches filled by the 4
inches in the receiver. Divide the result by 4, and you will have the depth
unit in the measure representing 1 inch of rainfall.
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