Page:Popular Science Monthly Volume 90.djvu/906

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��Popular Science Monthly

��A Trowel Which Places and Molds Concrete Curbs

AN adjustable trowel which greatly . increases the speed at which concrete

curbs can be made, has

been devised by Charles Upham, of Odell, Illi- nois. The mere ad- justing of its horizontal top-arm will vary the height of the curb as the trowel is pushed along over the roughly- shaped concrete previ- ously placed along the road.

The trowel is made in three pieces. The two side arms are held facing each other at the proper distance by the top arm between them. This arm slides up and down the slots shown in the side arms. In these the height ad- justments are made. The top arm is flared so that it continuously pushes the concrete downward while being guided over it. A more compact mass is thus formed than the ordinary flat trowel could produce.

���As the trowel is pushed along, the top arm is adjusted to the required height, thus shaping the concrete

��man, E. Bourdells, and an American, Captain Eley, have all three independently conceived the scheme of an arrangement in the stock which will prevent the rifle from being fired save at the correct angle.

The Frenchman's

idea is to place an electromagnet in the stock. The electro- magnet controls the ac- tion of the trigger and locks it normally against releasing the sear of the gun. A mercury column in the stock closes the electro- magnet circuit when the gun is held at the correct angle, unlocks the sear, and permits the soldier to fire the gun. If the angle is not correct, the mercury fails to touch both ends of the open circuit, and so the gun remains locked.

The German and the American ideas are practically alike in they make use of a

��principle in that

pendulum, or pivoted and swinging weight in the stock of the gun, to lock the sear against firing, save when the gun is at the correct angle to score hits.

��Three Separate Plans for Making a Gun Think

MILITARY rifle designers have little faith in the intelligence of troops. The crude and rough-and- ready sights they install and the fool- proof mechanism go to prove this. Their latest idea is to make the rifle refuse to fire when pointed at the wrong elevation — and even to fire itself when pointed at the correct one. Nearly all errors

��Range setter

���false trigger

��Mercury level Rackand sprocket

��Batteries

��in battle are er- rors in the eleva- tion of the rifle; the bullets strike too high or too low. The battle lines, being long, usually take care of side errors.

A German, A. Muller,aFrench-

��Adjustmg screw Distance and thread scale

���The French gun has an electromag- net in the stock which controls the trigger action

��The American gun, like that of the German, has a pivoted weight in the stock to lock the sear against firing except at the correct angle

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