890 



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 



