ry.

The instrument is put aside while the base is being made, or, if
you choose, have the base ready to receive the parts just
described when they are completed. Cut a base from a piece of
7/8-in. pine 3 in. wide and 40 in. long. In this base cut a groove
to fit the tube and the space to be occupied by the bottle is
hollowed out with a chisel to a depth of 3/4 in., so the bottle
rests on one-half of its diameter above the surface of the board
and one-half below. The instrument is made secure to the base with
brass strips tacked on as shown in the sketch. After the
instrument is in place put enough mercury in the bottle so the
depth of the mercury above the bottom end of the tube will be
about 1/2 in.

The scale is made on a piece or cardboard 2 in. wide and 4 in.
long. The 4 in. are marked off and divided into sixteenths, and
the inches numbered 27 up to 31. The scale is fastened to the base
with glue or tacks and in the position behind the tube as shown in
the sketch. Before fastening the scale, the instrument should be
compared with a standard barometer and the scale adjusted so both
readings are the same. But if a standard barometer is not
available, the instrument, if accurately constructed, will
calibrate itself.

In general, a drop in the mercury indicates a storm and bad
weather, while a rise indicates fair weather and in winter a
frost. Sudden changes in the barometer are followed by like
changes in weather. The slow rise of the mercury predicts fair
weather, and a slow fall, the contrary. During the frosty days the
drop of the mercury is followed by a thaw and a rise indicates
snow.

** Home-Made Post or Swinging Light [189]

Remove the bottom from a round bottle of sufficient size to admit
a wax or tallow candle. This can be done with a glass cutter or a
hot ring; the size of the outside of the bottle, which is slipped
quickly over the end. Procure a metal can cover, a cover from a
baking powder can will do, a lid fit it on the end where the
bottom was removed. The cover is punched full of holes to admit
the air and a cross cut in the center with the four wings thus
made by the cutting turned up to form a place to insert the
candle. The metal cover is fastened to the bottle with wires as
shown in the sketch. This light can be used on a post or hung from
a metal support.

[Illustration: Swinging Light]

** A Checker Puzzle [189]

Cut a block from a board about 3 in. wide and 10 in. long.