COMMEXCEMEXT EXERCISES 329 



before it can take the place of tlie steam eiij?ine. The turbine with 

 the aid of ihe electric motor has taken the place of the steam eug:ine 

 in some places within convenient distance from our waterfalls. But 

 electricity, as used for power, is in no sense a prime mover but simply 

 a means of transmittinj; i)Ower. Instead of competing with the steam 

 engine electricity has furnished it with a new field of labor, and the 

 requirements of this class of service have led to some marked improve- 

 ments in the engine. 



Liquid air is no more a prime mover than electricity, for we can- 

 not produce it without absorbing power and the law of the conserva- 

 tion of energy holds here as well as elsewhere. It may become useful 

 as a means of storing power however. 



We have no reason to expect that any of our sources of power will 

 go out of use, at least for a good many years yet. Horses, steam and 

 gas engines, water wheels and electric motors all have their uses and 

 their limitations. The mechanical disadvantages of the reciprocating 

 engine have led many a man to spend much time and labor trying to 

 devise a satisfactory rotary engine. 



One of the problems of the twentieth century will be to find a 

 source of energy adequate to meet the demands of what will be more 

 than ever an age of power. Our supply of fuel is limited and we can- 

 not expect our coal fields to supply us with power for many centuries 

 more if the present rate of use and increase keeps up. Will men then 

 learn to live without the aid of power, will they use coal more econo- 

 mically or will other forces be utilized? One improvement which 

 seems quite possible is the more economical conversion of heat into 

 other forms of energy. In the electric light we get about one-half 

 of one per cent of the energy of the coal consumed. The man who will 

 produce electrifity from coal economically will be given a chief place 

 among our inventors, and the man who can imitate the firefly and 

 glowworm in producing light without heat will not be far behind. 



Another field for the inventor is found in the storage of power. The 

 storage battery is about the only means now available. It is used to 

 some extent where the power available or required varies greatly, but 

 it is too heavy to be shii)|)ed from place to place. 



Liquid air contains nine times as much energj- as can be packed 

 into a storage battery of equal weight. It may possibly enable us to 

 bottle up the energy of Niagara and shij) it hundreds of miles to points 

 far beyond the reach of electrical transmission. 



But a pound of petroleum contains forty times as much energy as 

 one pound of li(|uid air and it can be sliipi)ed ami stored without loss. 

 If we could nianulai-ture a similar substance out of cheap materials we 

 might be able to store up the energy of the winds and our water 

 power and use it wherever and whenever we want it. We are already 

 using a simihir uieduid of jjroducing light. We light our bicycle lamps 

 and Some of our buildings with the energy of the St. Mary's river, 

 through the medium of calcium carbide and acetylene gas. 



There is a vast amount of water power yet to be utilized and, as 

 coal becomes moi-e exjiensive, fad dries may be driven to those localties 

 where it can be ol>tained. The Jive million horse power at Niagara could 

 run a monstrous manufacturing city and it would not be a smoky city 

 either. 



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