ts bottom closed by a funnel. The lower cylindrical part
holds a glass catcher into which the funnel delivers the water for storage
until the time when it will be measured in a graduated glass. The upper
part makes a good fit with the lower, in order to reduce evaporation to a
minimum.

Such a gauge can be bought for half a guinea or so, but one which, if
carefully made, will prove approximately accurate, can be constructed at
very small expense. One needs, in the first place, a cylindrical tin, or,
better still, a piece of brass tubing, about 5 inches high and not less
than 3 inches in diameter. (Experiments have proved that the larger the
area of the receiver the more accurate are the results.) 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. The measuring should
be done several times over, and the average result taken as the standard.
If the readings all agree, so much the better.

Preparing the Scale.--The next thing is to graduate a scale, which will
most conveniently be established in indelible pencil on a carefully
smoothed strip of white wood 1 inch wide. First make a zero mark squarely
across the strip near the bottom, and at the unit distance above it a
similar mark, over which "One Inch" should be written plainly. The distance
between the marks is next divided by 1/2-inch lines into tenths, and these
tenths by 1/4-inch lines into hundredths, which, if the diameter of the
re