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.  Sandpaper all the surfaces and round the edges slightly.  Mark out seven 1-in. squares on the surface to be used for the top and color the squares alternately white and black.  Make six men by sawing a curtain roller into pieces about 3/8 in. thick.  Number the pieces 1, 2, 3, 5, 6 and 7, and place them as shown in Fig. 1.  The puzzle is to make the first three change places with the last three and

[Illustration:  Position of the Men]

move only one at a time.  This may be done as follows: