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electricity in that direction. Moreover, the radio-active emissions. have the ef- fect of reducing the potential gradient and preventing explosive discharges between the cloud and the lightning rod.
It is easy to see the advantage of this arrangement. The difference of potential between the two electrified bodies being small, the spark will be of moderate intensity and the discharge unimportant; moreover, it will always take place by way of the lightning rod, and not at some distance there- from, as often happens, on account of the ionization of the air around its point.
A Glue Scraper
INSTEAD of buying glue scrapers for the shop, convert some of the worn- out files into useful articles.
Heat the end of a file red hot and beat it down to a sharp edge at the anvil. Then heat again and at a point about 1 % inches from the sharpened end, bend over at right angles. This end of the file should be heated again after bending and plunged into cold water to harden the steel, so that the sharp edge will last.
This instrument will make an excel- lent glue scraper which will render ef- ficient service in cleaning glue from jointed boards, and also from the top of the bench or work-table.
An Emergency Hack Saw SIMPLE yet efficient hack saw to fit an emergency can be made from a piece of iron wire % in. in
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���A hack-saw frame can be made from a piece of stout wire
diameter, bent as shown. The length depends on the size of the blades used. The wire is flattened at each end, and the blade is made fast by a rivet.
��Popular Science Monthly
Differential Gear for Home-Made Tractors and Cycle-Cars
A differential gear that can be made for home-made tractors or cycle cars consists of a main sprocket, or gear, mounted to run loosely on the ends of the two-piece counter-shaft, 6. The sprocket, and spur gear, are keyed on a short shaft which turns in a pillow block. The pillow block is bolted in the
���How to make a differential gear for a home- made tractor or cycle-car
main wheel about one-third of the dis- tance from the rim. The sprocket, and the gear, are keyed on the two counter- shafts. The small gears mesh together. An endless chain belt connects sprockets 1 and 3
A Useful Home-Made Glue Brush
AX excellent glue brush for the cab- inet maker or carpenter can be made from a piece of elm tree bark, which may usually be found in the yard of a furniture factory, wagon shop, or any hardwood lumber yard. With a sharp knife, whittle away the brittle out- er bark down to the white fibre, or in- ner side of the bark of which the brush is to be made ; cut a piece of this to the length and width required for the brush ; soak one end of this piece in hot water for a few minutes ; lay the water-soaked end on a hard substance, such as a piece of iron, or hardwood, and beat it out with a hammer, dipping it in the water occasionally to keep it thoroughly wet. The beating will cause the tough fibres of the bark to separate at the end, these forming an excellent and inexpensive brush, which never sheds hairs and- lasts longer than the cheap brush commonly sold at the stores.
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