The third State is Maine with 343,096 horse-power, over 2,707 wheels or an average of about 123 horse-power per wheel. Lack of space makes it impossible to enter upon a detailed description of the structural and mechanical features of the various plants and how they were operated for the purpose of turning water into an electric current. The best that can be done is to outline the most noteworthy features which typify the various situations under which power plants are developed and operated. The water power available under any condition depends principally upon two factors: First, the amount of fall or hydrostatic head on the wheels; second, the amount of water that can be turned over the wheels. The conditions vary according to place, there are all kinds of fall and flow. To develop a high power it is necessary to discharge a large volume of water upon properly designed wheels. In many of the western plants where only a small amount of water is available there is a great fall to make up for the larger volume in force coming down upon the wheels. So far as actual energy is concerned it makes no difference whether we develop a certain amount of power by allowing twenty cubic feet of water per second to fall a distance of one foot or allow one cubic foot of water per second to fall a distance of twenty feet. In one place we may have a plant developing say 10,000 horse-power with a fall of anywhere from twenty to forty feet and in another place a plant of the same capacity with a fall of 1,000, 1,500 or 2,000 feet. In the former case the short fall is compensated by a great volume of water to produce such a horse-power, while in the latter converse conditions prevail. In many cases the power house is located some distance from the source of supply and from the point where the water is diverted from its course by artificial means. The Shawinigan Falls of St. Maurice river in Canada occur at two points a short distance apart, the fall at one point being about 50 and at the other 100 feet high. A canal 1,000 feet long takes water from the river above the upper of these falls and delivers it near to the electric power house on the river bank below the lower falls. In this way a hydrostatic head of 125 feet is obtained at the power house. The canal in this case ends on high ground 130 feet from the power house and the water passes down to the wheels through steel penstocks 9 feet in diameter. In a great many cases in level country the water power can only be developed by means of such canals or pipe lines and the generating stations must be situated away from the points where the water is diverted from its course.