The Still engine can also be used as a common gasoline or gas engine of either two or four cycle and the efficiency in such types is from 31 to 33 per cent. This is much better than the best airplane engines, which show an efficiency under 27 per cent. Although 41 per cent for the best Still heavy-oil engine is a remarkable accomplishment, yet it does not begin to compare with the efficiency of the best water turbines and Pelton wheels, which turn into useful power from 75 to 87 per cent of the kinetic energy in the water that drives them.
CHAPTER XI
WHEN COAL AND OIL ARE EXHAUSTED
IN PREVIOUS chapters we have indulged in a great deal of historic retrospect. It may be well at this point, while we are dealing with the subject of power, to look into the future and the prospects that it holds out to us.
It was about fifty thousand years ago, according to conservative estimates, that primitive man first began to use tools, and he managed to exist and thrive and develop to a very high degree of civilization during practically the whole of that period without touching the stores of energy that lay beneath his feet. It was only yesterday that the steam engine was invented, and when it was discovered how to turn heat into work and what a wealth of power was stored up in the deposits of coal there started a lavish and profligate squandering of the precious heritage of the Carboniferous era. The fossilized vegetation of by-gone ages is now employed to drive our locomotives and steamships, to turn our factory wheels, to extract metals from the ore and help us shape them according to our needs and desires, to convert iron into steel and to heat and light our houses. We all know that there is a limited supply of coal in the world and that some day the stores will be exhausted, yet we go on using larger quantities of the fuel each year.
For the last century our demands for coal have been doubling every ten years, until to-day the world is using about 1,200 million long tons per year. It is conservatively estimated that if our demands for coal do not increase there is enough left in the whole world within a mile of the surface to last 1,500 years. Fortunately this country is better supplied than many others, and it is probable that we can get along on our present rations for 2,000 years. England, however, faces exhaustion of her coal supplies within two hundred years.
After living fifty millenniums on earth as a being clearly superior to other animals, man comes into an inheritance which he squanders in one or at most two millenniums. It is not creditable to our civilization that we have taken no precautions to ration out this precious store of fuel.