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a steam-engine. The revolution of the bobbin of the dynamo, which is effected by the steam-engine, generates a powerful current of electricity which is conveyed along one rail of the track to the train, and back again by the other rail, thus completing the circuit. The iron rails, in fact, take the place of the wires in an ordinary electric lighting circuit from one pole of the bobbin of the generator to the other. In crossing from one rail to the other the current passes through the bobbin of a dynamo fixed to the bottom of the traincarriage which serves as a locomotive, and in doing so it rotates the bobbin, and this rotation is communicated to the wheels of the carriage by a simple gearing which turns the axletrees. The bobbin of the dynamo is put in electrical connection with the rail conveying the current to it by a metal brush which sweeps the rail, and after passing through the bobbin the current reaches the other rail, which acts as the return wire, completing the circuit.

This plan of utilising the rails for the circuit of the current is, however, not always satisfactory, especially in wet weather, when the track is flooded and the insulating supports of the rail conveying the current from the generator to the bobbin in the first place are wetted. The moisture spoils the insulation of the rail and the electricity leaks into the earth.

In the Electric Tramway, at the Paris Electrical Exhibition last year, Dr. Siemens led the current to the dynamo on the car by way of separate conductors erected on posts beside the track, after the manner of a telegraph line. Each of the conductors consisted of a brass pipe split throughout its length and carrying a little metal chariot, which ran along the ground in

the pipe and served to connect it by means of a flexible conductor to the electric motor on the axle of the driving car.

In the system devised by Professors Ayrton and Perry rails are employed as the conductors of the current; but the enormous leakage over the whole of a long line of railway is obviated by insulating the rails in sections. When the train is on a particular section the weight of the carriages bends the rails of that section into contact with a special conductor carrying the current, and thus only the section which the train is passing over is electrified. This section may be made so short that the leakage from it is inconsiderable. In this way the train helps itself to the current it requires as it goes along, and all the railway, both before and behind it, is unelectrified. A dynamo is fixed to every carriage, or it may be to every axle, and is supplied with current from the rails below through the wheels themselves as they press upon the rails beneath and bend them into contact with the conductors coming from the generator stationed at the end or some intermediate point of the route. In this way a high speed can be attained ; and, moreover, an absolute block system is created, for only one train can be propelled on one section at a time.

Electric railways are likely to prove very useful for short local lines where the gradients are very steep or the atmosphere is apt to become close, as in the St. Gothard Tunnel and the Metropolitan District Railway. They are free from steam and coal smoke, or noise and cinders, and hence are peculiarly suitable for the interior of cities. Several schemes for building them are already promoted in this country,

notably a tramway from Portrush to Bushnells, near the Giant's Causeway, in the north of Ireland, and a line under the Thames from Charing Cross to Waterloo. It has also been proposed to carry letters by underground post on this plan, and the suggestion is a good one, for the distance traversed may be far greater than by the pneumatic despatches now in vogue. In Paris an electric railway has been projected along the boulevards, and we also learn that an electric tramway has been introduced into the bleachfields of the Breuil-enAuge (Calvados), France, where it transports the linen to the grounds with a cleanliness which could not be obtained with steam-power. As another application of electric power it should also be mentioned that the same dynamo which pulls the waggons full of linen is also used to turn the reels which wind and unwind the webs of cloth as they are spread upon or lifted from the grass.

The electric power in the case of the Bleachfield Tramway is not sent along the rails from the generator direct, but is derived at second-hand from sixty Faure secondary batteries or accumulators, carried by the tender of the train. This mode of "storing” the electric current will be serviceable in the case of street tramcars and omnibuses, which cannot very well have the electricity sent to them by special conductors. They will have to preserve their independence of action by taking their own supply of power with them, and the Faure or the Sellon accumulators will enable them to do so. Twenty accumulators freshly charged at the terminal station by a dynamo-electric generator will enable an omnibus or tramcar to run a whole halfday, and the exhausted accumulators can be readily

replaced by charged ones or themselves charged afresh.

Boats, tricyles, and even balloons can be supplied with power in the same way, but as yet very little has been accomplished in this direction, if we except the trials made by M. Trouvé, of Paris, in his boat on the Seine, and the toy balloon exhibited by M. Tissandier at the recent Paris Electrical Exhibition. In both these instances the power was derived from batteries, and the propeller of the vehicle was driven by a Trouvé electric motor.

Figure 76 shows the arrangement adopted by M. Trouvé to drive his boat. There we have a small Trouvé motor, consisting of two electro-magnets forming a frame enclosing a Siemens bobbin of wire which rotates between the poles of the magnets when a current is passed through it by connecting wires. The rotation of the bobbin is communicated by proper gearing and a cord to a pulley which is fixed on the shaft of the propeller or screw. This propeller is carried by the rudder, which is cut so as to admit it. Fitted with this apparatus, and deriving its motive power from a battery of 12 large elements, M. Trouvé's little craft The Telephone sped up the Seine on the 26th of May, 1881, against the tide at the rate of 34 miles per hour. The boat was about 18 feet long by 3 feet 6 inches wide and carried three persons. . The total weight of the motor and batteries was about 64 lbs.

As long ago as 1839 M. Jacobi, the famous Russian electrician, made a trip on the Neva in a boat propelled by the current from a battery of 128 Grove cells, actuating a peculiar motor of his own device. The boat was urged by paddles and ascended the Neva with twelve passengers on board. So powerful was the electric current from the battery that it heated white

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hot 6 feet of platinum wire as thick as a darning needle; but though the speed was satisfactory the fumes from the acid battery rendered the voyage anything but pleasant.

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