This instrument is often very convenient. When wishing to have a true sketch, you trace it on the glass; you then transfer it to an oil-paper, and again on drawing paper if the former is not to be used. Besides, if one has an exact sketch on whatever paper, you may reproduce it in freehand, if you are blessed with any idea of drawing.
If the varnished plane has to serve again, wash it with warm water, and let it get dry; then the varnishing can be done over again.
Camphor in Water.
If you put very small pieces of camphor on the water, you will see them turn round each other with great velocity. These movements are due to the diminution of the superficial tension of the liquid in the vicinity of the pieces of camphor.
In order to stop them throw a drop of oil in the water, and you will produce a perfect calm. One may utilize the camphor for an amusing recreation.
Construct a small paper or cardboard boat and fasten underneath on the hind part or stern a piece of camphor. Your boat will maneuver on the water. Persons not initiated will be much puzzled, and be long to find out by what contrivance this small craft is propelled.
A Simple Multiplier.
Write on a card or strong paper the letters, figures, etc., which you want to reproduce. Then all along the lines or tracing, with a needle, prick holes in close proximity at equal distances.