274 SCIENCE IN SHORT CHAPTERS. 



tapping of a rock-cavity containing oil of such varying densities and 

 volatility that some of it flew out as a vapor, or boiled at the mean 

 temperature of the air of the country or that of the surrounding 

 rocks. Such being the case, the cavity was filled with high-pressure 

 oil-vapor straining to escape. If the bore-hole tapped the crown or 

 highest curve of the roof of such an oil cavern, it opened directly 

 into the vapor there accumulated, and the vapor itself rushed out 

 with such force that a pillar of fire was raised in the air if a light 

 came within some yards of the orifice. We are told of heavy iron 

 boring-rods that were shot up to wondrous heights and we may be- 

 lieve these stories if we please. 



If the bore-hole struck lower down, somewhere on the sloping sides 

 or in the shallow lower branches of the oil-cavern, it dipped at once 

 into liquid oil, and this oil, being pressed by the elastic vapor of the 

 upper part, was forced up as a jet of spouting oil. 



In either case these violent proceedings soon came to an end, for 

 as the vapor or oil poured out, the space above the oil-level where the 

 vapor had been confined was increased, and its pressure diminished, 

 till at last it barely sufficed to raise the oil to the surface, and after- 

 ward failed to do that. 



It is quite clear from this that the supplies are not ' ' inexhausti- 

 ble." The quantity of vapor having been limited, there must also 

 be a limit to the quantity of oil giving off this vapor ; the space in 

 the oil- cavern occupied by this vapor having been limited, there must 

 be a limit to the space occupied by the oil. The quantity of oil may 

 be ten times, a hundred times, a thousand times, or ten thousand 

 times, greater than that of the vapor, but in either or any case it 

 must come to an end at last, sooner or later. 



If there were but a few wells here and there, as at other similar 

 places, such as Rangoon, the Persian oil-wells, etc., the pumping 

 might continue for centuries and centuries ; but this is not the case 

 in America. The final boundaries of the oil-bearing strata may not 

 yet have been reached ; but so far as they are known they are riddled 

 through and through, and pumped in every direction, so that the 

 end must come at last, though with our present knowledge we cannot 

 say vihen. 



We can, however, say how it must come. It will not be a sudden 

 stoppage, but a gradual exhaustion indicated by progressive diminu- 

 tion of supply. We shall not be suddenly deprived of this important 

 source of light and cheerfulness ; but we may at any time begin to 

 feel the pinch of scarcity and consequent rise of price. This rise of 

 price will check the demand, and bring forward other supplies from 

 sources that now cannot be profitably worked on account of the 

 cheapness of American petroleum. 



Many of the countries now largely supplied from America have oil- 

 springs of their own, which a rise of price will speedily l>ring into 

 paying operation. 



We have nothing to fear. The fact that in spite of the ruinous 

 prices that have recently prevailed the Scotch oil-makers continue to 

 exist at all, shows us what they may do with a rise of even a few 

 pence per gallon. The thickness and area of the dark shales from 

 which their oil is distilled are so great that their exhaustion is very 

 far remote indeed. The Americans have similar shales to fall back 

 upon when the spontaneous product ceases to flow, but they are 



