FORECASTING THE PROGRESS OF INVENTION. 309 



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 uni- 

 form 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 out- 

 put ; therefore, when the apparatus was working at its full capa- 

 city, there would be a large surplus of power going to waste. By 

 increasing the capacity of the storage reservoirs, the average out- 

 put 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 max- 

 imum output, it would probably be profitable to make the capa- 

 city 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 ap- 

 parently reasonable to assume that they would constitute a more 

 economical form of power, but wherever a constant supply is de- 



