and chain. Here again the power is drawn from a generating dynamo.

The electric hammer of M. Marcel Deprez consists of a hollow column or solenoid, built up of coils of wire placed one above another. This solenoid is supported on a table, and contains within it a stem or core of soft iron which has a hammer head fixed to its lower end. The separate coils forming the solenoid are connected to the contact pieces of a circular commutator in such a manner that though they are all joined together end to end, a wire runs from each junction of a pair of coils to one of the commutator contacts. Two metal brushes can be made to sweep one of these contacts by turning a handle, and as the current enters and leaves the coils by the two brushes, the number of coils and their position in the column will be determined by the angle between the two brushes and the position of the handles. Thus if there are ten coils included between the two brushes the current will traverse these ten coils, and if the handles be made to sway round the commutator with a see-saw motion the current will travel up and down the solenoid, exciting ten coils at a time. The soft iron core will be attracted by the excited coils, and hence will rise and fall in the hollow solenoid following the march of the excited coils. In this way an up and down motion will be given to the

hammer head.

In passing from out-of-door operations to the duties of the household, we come to the small electric motors which have been devised for driving sewing-machines, lathes, punkahs, coffee-mills, and such-like appliances. Motors of this kind have been constructed by M. Trouvé, M. Marcel Deprez, Jablochkoff, and others;

but perhaps the most efficient of these for its size and cost is a pigmy motor, invented by Mr. W. W. Griscom, of Philadelphia.

This apparatus is illustrated in Fig. 77 in the act of

driving a sewing-machine. It consists of an electromagnet in the form of a flat ring of soft iron wound on its opposite sides with insulated wire. Two bare zones of the ring above and below, act as "north" and "south" poles. Between these poles is placed a movable bobbin, with poles like an electro-magnet, to which

the current is led by terminals and commutator brushes. The current traverses alike the coils of the ring electro-magnet, and the bobbin thereby rotates the latter, and drives a pulley which communicates its motion by a strap to the pulleys of the sewing machine.

This motor is peculiarly powerful, owing to the fact that the currents induced in the coils of the magnet by the rotation of the bobbin with its magnet poles inside it, are caused to assist the magnetising current supplied to the ring coils by the commutator, and thus heighten the magnetism of the ring poles.

In form it is only two inches and a half long by two inches in diameter, and weighs two pounds and a half. Nevertheless, with the current from a battery of six bichromate of potash cells running throughout the bobbin, it attains a speed of 5,000 revolutions per minute, and yields sufficient power to drive a sewingmachine or a small lathe at a rapid rate. As exhibited at the Crystal Palace, the bichromate of potash battery for working the machine is contained in a box, and the power of the battery, and thus the speed of the machine, can be regulated at the will of the seamstress, by working a pedal with her feet, and raising or lowering the battery-plates in the solution which surrounds them. The greater the extent of plate-surface immersed in the liquid the greater the current obtained from the battery, and the more energetic the action of the motor and machine. According to the vendors the estimated cost of working this little motor is about 1d. per hour per horse-power of energy obtained.

When the electric light and power corporations have been fairly launched, and central stations for

generating electricity and distributing it to houses and factories have been established, the application of the electric current to motive purposes will come more and more into fashion. A hundred little services will be performed by it which are now done by manual labour or by steam and other sources of power. The same wires which convey the current for lighting the rooms of a home will serve to deliver it for driving the sewing-machine or grinding the coffee. Moreover, a mechanic or watchmaker will be able to drive his lathe by it; and it is probable that the old habit of craftsmen working at home will be to some extent revived, since it will be possible to have power brought there like gas or water. The great economy of very large steam-engines over small ones has led to the development of large factories, where hundreds of human beings are cooped up amid the ncessant roar of machinery and the stifling dust of a polluted atmosphere. But when power has been distributed by wire to this place and to that, a blow will have been struck at this imprisonment of men and women in the interests of capital, and the consequent deterioration of their souls and bodies. That power on a large scale can be distributed in this way has been already demonstrated, and Sir William Thomson, amongst others, has shown that the cost for conductors capable of transmitting hundreds of horse-power need not be excessive. He even proposes to utilise some of the power of Niagara Falls to light the towns and drive the mills for a hundred miles around. Whether this be done or not, it is certain that the power of waterfalls in hilly countries, which is now largely wasted, will be utilised for electric light and motive purposes.

All Glasgow, for instance, could be lighted by the Falls of Clyde, and many of the great steam-hammers in its shipyards driven to boot. Wind, too, will be utilised as a primary source of electric power; for, though variable and inconstant, it can be made to turn dynamos which will store the electricity they generate in accumulators, from which a constant current can be obtained. The intermittent power of the tides and of river floods may also be turned to account in a similar way; even the induced currents of the atmosphere in lightning-rods may be stored up, as well as the currents generated in thermo-piles by the solar heat, and thus we shall have the light of day made captive for the uses of the night, and the very lightning flash submitted to the services of man.