Page:Popular Science Monthly Volume 51.djvu/321

Rh a matter of fact, a great deal of ingenuity has been displayed in this direction, and the cost of the mechanism, with reference to the power recovered, has probably been reduced to nearly as low a point as is possible. In the matter of simplicity and durability equally good results have been obtained.

An analysis of the most salient features of these forms of energy will show why they are not utilized on a more extensive scale. The power of waves and tides is only available along the seacoast, where, as a rule, power is not in demand; furthermore, any kind of apparatus made to utilize this energy must be very strong and bulky in comparison with the power it will give, and as a consequence very costly. In addition to this, the amount of energy will vary greatly at different seasons; hence the output that can be depended upon at all times must be far below the actual capacity of the apparatus. A further drawback is the great irregularity of the power, which renders it of little value unless means are provided for reducing it to a delivery at a uniform rate.

Windmills are not so much restricted, as to location, as the foregoing, but they are very large in comparison to the work they can do, and, as the velocity of the wind may drop to nearly zero for a long period of time, their average capacity, taking the year through, may be exceedingly small.

Solar energy is available everywhere, but the capacity of an apparatus made to utilize it would be very indefinite and far below its maximum, owing to the fact that cloudy weather may come at any time and continue for days or even weeks.

The irregularity of the power derived from these sources can be overcome by resorting to some form of storage, but this would not help, except to a limited extent, to increase the average output; therefore, when the apparatus was working at its full capacity, there would be a large surplus of power going to waste. By increasing the capacity of the storage reservoirs, the average output could be increased, and if the intervals of time during which the energy developed is little or nothing were short, say two or three days, and were followed by corresponding intervals of maximum output, it would probably be profitable to make the capacity great enough to store all the surplus developed at times of maximum output; but, as these periods may each extend over two or three weeks, it is evident that about the best we can do is to increase the average output slightly by using a greater storage capacity.

As these natural forms of energy can be obtained without cost, and the fuel used by a steam engine has to be purchased, it is apparently reasonable to assume that they would constitute a more economical form of power, but wherever a constant supply is