NATURAL PHILOSOPHY. 101 



this piston is attached a double crank, which gives motion to a shaft, 

 on which is a fly-wheel. Attached to one side of the piston is an arm, 

 which works the cut-off. The battery wires are screwed to two rods 

 of copper, one running along one side the whole length of the coils, 

 the other close to the coils on a narrow platform on the engine frame. 

 Small blocks of copper, connected with the hollow coils by wires, form 

 the connecting points in the circuit, and perform a similar office to the 

 ports of a steam-engine. Attached to a slide, moved by the arm con- 

 nected with the piston, are two thin strips of copper, separated a short 

 distance at the middle part. Each strip has two metal spring plates, 

 always in contract with the copper blocks. Of these plates, two only 

 are in connection with the battery at once. As the plates, by the 

 motion of the arm, move backwards and forwards, the circuit is formed 

 alternately, from coil to coil, cutting off the current behind and throw- 

 ing it ahead. The stroke of the engine is reversed by throwing the 

 current from one half the coils to the other half. This is done by two 

 dogs, or projections, fixed on the side of the frame, which strike against 

 a charger fixed on a centre-pin. When this charger strikes one pro- 

 jection, it brings one set of slides, or plates, to form the circuit ; and 

 when' it strikes upon the other projection, it turns upon its pin and 

 comes in contact with the strip of copper attached to the other slides ; 

 there is therefore three of the coils always charged at once. When- 

 ever a full stroke has been made, the charger at once diverts the cur- 

 rent from one half the coils to the other, acting upon the opposite end 

 of the piston ; the three coils near the middle, being first charged, and 

 so on, one after another, as the piston moves along. A stroke of any 

 length can thus be given to the engine, a matter never before accom- 

 plished. Scientific American. 



ELECTRO-MAGNETIC TRACTION ON RAILWAYS. 



TIIE idea of increasing the adhesiveness of the wheels of locomo- 

 tives, without increasing their weight, has, for a number of years past, 

 occupied the attention of mechanicians. To effect this, a plan has 

 been presented to the French Academy, by Mr. Nickles, to convert the 

 wheel of the locomotive into a magnet, and make it stick to the iron 

 rail by a like adhesion. This he does by placing a galvanic battery 

 under the body of the engine. A wire coming from the poles of this 

 battery is then coiled horizontally round the lower part of the wheel, 

 close to the rail, but in such a way that the wheel turns round freely 

 within it, fresh portions of its circumference coming continually into 

 relation with the coil. The part of the wheel in immediate contact 

 with the rail is thus made magnetic, and therefore has a strong adhe- 

 sion for the surface along which it moves, and the amount of the 

 adhesion may be increased or diminished at any time, by merely aug- 

 menting or reducing, the intensity of the galvanic current that circu- 

 lates through the surrounding coil. By means of a handle the 

 electricity may be turned on or off, and an effectual brake be thus 

 brought into activity, that can make the iron rail smooth or adhesive 

 according to the requirements of the instant, and this without in any 



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