The stove is supported upon an axle through the intermedium of two angle irons riveted longitudinally upon the cylinder.  The axle is cranked, and its wheels, which are of wood, are 41/2 feet in diameter.  The shafts are fixed to the angle irons.  The apparatus is, in addition, provided with a seat, a brake, and prop rods before and behind to keep it horizontal when in operation.

The boiler that supplies this stove is vertical and is mounted upon four wheels.  It is jacketed with wood, and is provided with a water level, two gauge cocks, a pressure gauge, two spring safety valves, a steam cock provided with a rubber tube that connects with that of the stove, an ash pan, and a smoke stack.  In the rear there are two cylindrical water reservoirs that communicate with each other, and are designed to feed the boiler through an injector.  Beneath these reservoirs there is a fuel box.  In front there is a seat whose box serves to hold tools and various other objects.—­La Nature.

* * * * *

AN ELECTRICAL GOVERNOR.

We abstract the following from a paper on electric lighting by Prof.  J.A.  Fleeming, read before the Iron and Steel Institute, Manchester.  The illustration is from Engineering.

[Illustration:  ELECTRICAL GOVERNOR.]

One of the questions which most frequently occurs in reference to mill and factory lighting is whether the factory engines can be used to run the dynamo.  As a broad, general rule, there can be no question that the best results are obtained by using a separate dynamo engine, controlled by a good governor, set apart for that purpose.  With an ordinary shunt dynamo, the speed ought not to vary more than 2 or 3 per cent. of its normal value on either side of that value.  Hence, if a dynamo has a normal speed of 1,000, it should certainly not vary over a greater range than from 970 to 980 to 1,020 to 1,030.  In many cases there may be shafting from which the necessary power can be taken, and of which the speed is variable only within these limits.  There are several devices by which it has been found possible to enable a dynamo to maintain a constant electromotive force, even if the speed of rotation varies over considerable limits.  One of these is that (see illustration) due to Messrs. Trotter & Ravenshaw, and applicable to shunt or series machines.

In the circuit of the field magnet is placed a variable resistance.  This resistance is thrown in or out by means of a motor device actuated by an electromotive force indicator.  A plunger of soft iron is suspended from a spring, and hangs within a solenoid of wire, which solenoid is in connection with the terminals of the dynamo.  Any increase or diminution of the electromotive force causes this iron to move in or out of the core, and its movement is made to connect or disconnect the gearing which throws in the field magnet resistance with a shaft driven by the engine itself.  The principle of the apparatus is therefore that small variations of electromotive force are made to vary inversely the strength of the magnetic field through the intervention of a relay mechanism in which the power required to effect the movement is tapped from the engine.