270 UTILIZING THE SUn's ENERGY. 



objection of large cost per unit of power delivered. Whether this 

 cost will be so great as to balance the gain coming of free delivery to 

 the machine of the energy to be transformed can be known only when 

 we are driven to the serious task of providing substitutes for the heat 

 engines. 



Ericsson made a working steam engine deriving its energy from the 

 direct rays of the sun, and proved that either steam or air could be 

 employed in such an engine as the working fluid. He also showed 

 what is the amount of power practically derivable from the sun's rays 

 through this method of utilization of the heat of the sun. 



Later testimony, so far as it goes, confirms his statements, and the 

 mechanical possibility is beyond question that, in future centuries, 

 when our fuels are gone, we may largely utilize the sun's energy in 

 this manner. But it may yet be found that this threatened exhaustion 

 of our fuel supplies is not the only, or perhaps even the first, limit 

 likely to be set to the progress of the world of humanity on our globe. 

 The exhaustion of our iron ores, like our platinum deposits, the min- 

 gling with the air of the products of combustion of our fuels while they 

 still last, the pollution of our water supplies, and many other possible 

 obstacles to progress and growth, will have their effects, individual 

 and combined, and our most serious problems are quite likely to be 

 found at an earlier date than that of the loss of our fuels; the last- 

 named danger is, in fact, already upon us. This generation need not 

 attempt to cross the first of the bridges on the list, although a very 

 seductive problem is presented to the engineer. This problem may 

 be enunciated thus: 



To find a system of gathering and storing the energy of the direct 

 rays of the sun, for utilization in power production, by a special form 

 of heat motor; to find, next, a method of transforming the energy 

 thus collected into mechanical power; and to discover a method of 

 storing, for later use, excess power obtained during periods of sunshine, 

 tiding over the sunless periods. 



The problem will be solved only when the system thus perfected is 

 so designed and constructed as to be able to provide power for indus- 

 trial purposes so cheaply that a business profit can be made through 

 its use. 



