the stored energy of coal, whether directly in the steam engine or indirectly in the dynamoelectric machine and the electric motor. With the end of the coal age already well in view, we can only conjecture what the sources of mechanical power will be a hundred years hence. Before we have quite exhausted our coal measures and begun to draw more liberally on our stores of petroleum, we shall no doubt have abandoned altogether so wasteful a contrivance as the steam engine. There is a clumsiness almost barbarous in the roundabout employment of coal to produce heat, the steam engine to utilise only a miserable fraction of the potential energy even of the part of the coal which we do not fatuously allow to escape as smoke; of the dynamo to use up a part of the motion yielded by the steam engine in producing electricity (while a small but recognisable portion of that motion is converted wastefuily back again into heat), and of the electro-motor to re-convert the electricity into motion, heat, light and chemical energy, according to our requirements, It cannot be many years before we learn to use coal far more economically than we do nowadays, abolishing the furnace and the steam engine, and obtaining electricity directly from coal itself by some sort of electro-chemical decomposition. But even so, our coal will not last much longer. The speed of our progress will exhaust it much
