In many parts of the world, especially in America, water power is utilized to a considerable extent instead of steam for the generation of electric current. The immense volume of water passing over the Falls of Niagara develops energy equal to about seven million horse-power, and a small amount of this energy, roughly about three-quarters of a million horse-power, has been harnessed and made to produce electric current for light and power. The water passes down a number of penstocks, which are tubes or tunnels about 7 feet in diameter, lined with brick and concrete; and at the bottom of these tubes are placed powerful water turbines. The falling water presses upon the vanes of the turbines, setting them revolving at great speed, and the power produced in this way is used to drive a series of very large alternating current dynamos. The current is conveyed at a pressure of about 60,000 volts to various towns within a radius of 200 or 300 miles, and it is anticipated that before very long the supply will be extended to towns still more distant. Many other American rivers have been harnessed in a similar way, though not to the same extent; and Switzerland and Norway are utilizing their water power on a rapidly increasing scale. In England, owing to the abundance of coal, little has been done in this direction. Scotland is well favoured in the matter of water power, and it is estimated that the total power available is considerably more than enough to run the whole of the railways of that country. Very little of this power has been utilized however, and the only large hydro-electric installation is the one at Kinlochleven, in Argyllshire. It is a mistake to suppose that water power means power for nothing, but taking things all round the cost of water power is considerably lower than that of steam. CHAPTER XI ELECTRICITY IN LOCOMOTION