Another appliance used in the power-house, chiefly for handling heavy loads and transferring them from one point to another, is called the electric crane. It is mounted upon tracks located on each side of the power-house. The crane spans the whole distance, and runs on this track by means of trucks from one end of the power-house to the other. Running across this crane is another track which carries the lifting-machinery, consisting of block and tackle, able to sustain a weight of fifty tons. Situated at one end of the crane are one or more electric motors, which are able, under the control of the engineer, to produce a motion in any direction, which is the resultant of a compound motion of the two cars acting crosswise to each other together with the perpendicular motion of the lifting-rope connected with the block and tackle. It seems like a thing endowed with human reason, when we see it move off to a distant part of the building, reach down and pick up a piece of metal weighing several tons, carry it to some other portion of the building and lower it into place, to the fraction of an inch. While the machine itself does not reason, there is a reasoning being at the helm, who controls it and makes it subservient to his will. The machine is to the engineer who manipulates it what a man's brain is to the man himself. The brain is the instrument through which the unseen man expresses his will and impresses his work upon men and things in the visible world. CHAPTER XXIV. NIAGARA FALLS POWER--APPLIANCES. In the last chapter I described some of the appliances used in connection with the power-house. There are many things that are commonplace as electrical appliances when used with currents of low voltage and small quantity, that become extremely interesting when constructed for the purpose of handling such currents as are developed by the dynamos used at Niagara. For instance, it is a very commonplace and simple thing to break and close a circuit carrying such a current as is used for ordinary telegraphic purposes, but it requires quite a complicated and scientifically constructed device to handle currents of large volume and great pressure. If such a current as is generated by a dynamo giving out 5000 horse-power under a pressure of 2200 volts should be broken at a single point in a conductor, there would be a flash and a report, attended with such a degree of heat and such power for disintegration that it would destroy the instrument.