ceiver is four times that of the tube, will be about 3/16 inch apart. For
reading, the scale is held against the tube, with the zero mark level with
the top of the cork plugging the bottom. It will, save time and trouble if
both tube and scale are attached permanently to a board, which will also
serve to protect the tube against damage.

Making the Receiver.--A tin funnel, fitting the inside of the receiver
closely, should be obtained, or, if the exact article is not available, a
longer one should be cut down to fit. Make a central hole in the bottom of
the receiver large enough to allow the funnel to pass through up to the
swell, and solder the rim of the funnel to the inside of the receiver,
using as little heat as possible.

If you select a tin of the self-opening kind, you must now cut away the top
with a file or hack-saw, being very careful not to bend the metal, as
distortion, by altering the area of the upper end of the tin, will render
the gauge inaccurate.

The receiver should be supported by another tin of somewhat smaller
diameter, and deep enough to contain a bottle which will hold 3 or 4 inches
of rainfall. In order to prevent water entering this compartment, tie a
strip of rubber (cut out of an old cycle air tube) or other material round
the receiver, and projecting half an inch beyond the bottom (Fig. 152).

All tinned iron surfaces should be given a couple of thin coats or paint.

The standard distance between the rain gauge and the ground is one foot.
The amount caught decreases with increase of elevation, owing to the
greater effect of the wind. The top of the gauge must be perfectly level,
so that it may offer the same catchment area to rain from whatever
direction it may come.

[Illustration: FIG. 153.--Self-measuring gauge.]

Another Arrangement.--To simplify measurement, the receiver and tube may
be arranged as shown in Fig. 153. In this case the water is delivered
directly into the measure, and the rainfall may be read at a glance. On the
top of the support is a small platform for the receiver, its centre
directly over the tube. The graduations, first made on a rod as already
described, may be transferred, by means of a fine camel's hair brush and
white paint, to the tube itself. To draw off the water after taking a
reading, a hole should be burnt with a hot wire through the bottom cork.
This hole is plugged with a piece of slightly tapered brass rod, pushed in
till its top is flush with the