124 



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 



A 



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 bv 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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