UTILIZING THE SUN's ENERGY. 269 



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

 lirainar}' s3^mptoms — difficult}' in mining- and increased price of the 

 fuel in the market, as well as the expressed anxiet}' of statesmen guard- 

 ing the interests of the great manufacturing districts of Europe. 



The ultimate outcome nnist he the gradual extinction of our fuel 

 supplies, and if no sulxstitute can be devised b}" 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 necessar}' to the maintenance of civilized life as we know it 

 to-day. 



While it may be true, as has recenth' 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 define the word. 



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

 and the utilization of the energy' of the direct ra3's of the sun. The 

 last, though apparently most universalh' available, has hitherto been 

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

 have been very extensiveh' emplo3'ed, the deduction being that the 

 former process presents elements of peculiar difficult3^ 



Water power is, to date, the most available, and the common substi- 

 tute for the heat engine. AN'hen the existing waterfalls are generally 

 utilized, they will go far toward meeting the needs of the race in power 

 production, and the coincident use of the electric current for the dis- 

 tribution of energy from its source is now making this element of the 

 problem far more promising of solution than previousU'. 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 generallv 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- 

 tinuit}' of action are not important, will probably be found in great 

 part unavailable for large powers or for the great majorit}' of uses 

 which commonly demand steadiness of power and action. 



Solar motors make available an immense quantity of active energy 

 by direct utilization. Thev are evidently practicable in the sense that 

 there is no inherent mechanical difficult}" in their construction and 

 operation. The}" 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 



