UTILIZING THE SUN'S ENERGY. 269 



is, in fact, in some portions of the world already presenting its pre- 

 liminary symptoms — difficulty in mining- and increased price of the 

 fuel in the market, as well as the expressed anxiety of statesmen guard- 

 ing the interests of the great manufacturing districts of Europe. 



The ultimate outcome must be the gradual extinction of our fuel 

 supplies, and if no substitute can be devised by the ingenuity of man, 

 the compulsory retreat of the civilized races into the tropics, and, 

 even there, the interruption of the manufacturing industries on the 

 scale necessary to the maintenance of civilized life as we know it 

 to-day. 



While it may be true, as has recently been estimated, that the belt 

 extending thirty degrees on either side of the equator may be capable 

 of sustaining a population of ten thousand millions, over ten times the 

 number now inhabiting that portion of the globe, such a population 

 will require correspondingly increased power supplies, if it is to be a 

 civilized population as we to-day detine the word. 



The available sources of power remaining arc wind and water power, 

 and the utilization of the energy of the direct rays of the sun. The 

 last, though apparently most universally available, has hitherto been 

 unused, while the indirect systems of employment of the sun's energy 

 have been very extensively emplo3 T ed, the deduction being 

 former process presents elements of peculiar difficulty. 



Water power is, to date, the most available, and the comm 

 tute for the heat engine. When the existing waterfalls are 

 utilized, they will go far toward meeting the needs of the rac« 

 production, and the coincident use of the electric current fo. 

 tribution of energ}^ from its source is now making this element of the 

 problem far more promising of solution than previously. Yet it is 

 doubtful whether water power will suffice for all the requirements of 

 later generations, even though the usual result of stimulated brain work, 

 checking of the growth of population, should hold down the numbers 

 of the human race to something like those of the present time. 



Wind power, although even more general^ distributed than water 

 power, is subject to its own peculiar disadvantages for our purposes, 

 and, while likely to come more and more into use for purposes like 

 that of raising water to higher levels, and where steadiness and con- 

 tinuity of action are not important, will probably be found in great 

 part unavailable for large powers or for the great majority of uses 

 which commonl}' demand steadiness of power and action. 



Solar motors make available an immense quantity of active energjr 

 by direct utilization. They are evidentl} r practicable in the sense that 

 there is no inherent mechanical difficulty in their construction and 

 operation. They are subject, however, to the same defects of lack of 

 steadiness of source of energy, of need for provision for extensive and 

 prolonged storage, if to be generally employed, and to the serious 



