The chimney top with the dowel attached to it below is made to revolve so that the Hygroscope may be adjusted. To make the chimney top, bore a 1/4" hole into the end of a 1/2" dowel; then saw it off 1/2" and glue in the upper dowel. Make the turntable somewhat round at each end. In the center of it, glue and nail the lower dowel. Next, paint the house if desired. The violin string is glued and wedged into holes in the upper and lower dowels so that the turntable will swing 3/16" above the floor.
The man and woman may be made of cardboard, wood, clay, chalk or plaster of Paris; or they can be bought at a toy store. Painted in bright colors and shellacked, or varnished, they look well. They can be made to balance on the turntable by adding a piece of lead. Of course, neither they nor the turntable should touch any part of the house as they swing around.
HYGROSCOPE OR WEATHER COTTAGE — Plate 17
[ELECTROPHORUS—][Plate 18].
The electrophorus consists of two parts, a pan filled with a resinous mixture, and a cover which has been completely covered with tinfoil. Under favorable conditions, a spark of electricity 1/2" long can be obtained from this electrophorus. The favorable conditions are these: The air should be dry; both parts of the electrophorus should be warm, dry, and clean; and the tinfoil and rosin should be perfectly flat, so as to come in close contact with each other.
Make the pan and its sides as shown in [Plate 18]. Glue and nail the sides in place and round their upper edges well with sandpaper. To make the resinous mixture, melt a half teacup of rosin with two teaspoons of turpentine and about the same of paraffin in a rather deep dish, and pour the mixture into the pan. As all these materials are inflammable, perhaps the safest place to melt them is in the oven. After the pan is cold, test the surface of the rosin to see that it is flat every way. If it is not flat, sandpaper the high parts slowly with coarse sandpaper.