HAWORTH. | Gas Pressure. 185 
water in one case would rise only to within 200 feet of the 
surface and in another case would rise 100 feet above the sur- 
face, then the same water pressures might be sufficient cause 
for a difference in gas pressure. 
Another difficulty of understanding gas pressure is the man- 
ner of decline in a gas-well when used. It seems to be univer- 
sally true that as the gas becomes exhausted in a well from use 
the pressure declines gradually. Why should this be so? If 
the pressure in any way is due to water pressure, why should 
it decline gradually by use? For example, suppose we have 
an ordinary gas-receiver instead of the sandrock, and suppose 
that a pipe 1000 feet high connected with this is filled with 
water; it would then give a gas pressure in the receiver of 
about 430 pounds. Should the valve be opened and the gas 
allowed to escape water would gradually take its place, and the 
only decrease in pressure would be the decrease in height of 
the water column. If we change the gas-receiver in our prob- 
lem to a gas-sand 20 feet thick with the bottom 1000 feet un- 
derground, then the pressure should decline only the amount 
produced by a column of water 20 feet high, or about eight 
pounds. And so long as any gas can be obtained at all we 
should have a pressure equal to the initial pressure minus this 
small amount. 
But no natural-gas wells decline in this manner. A well 
with an initial pressure of 500 pounds in the course of time will 
drop to 400, then to 300, then to 100, then to 50, and to still 
smaller fractions if it is used longer. Should gas pressure be 
due to the gas being manufactured in the ground until a cer- 
tain pressure is established then we would expect it to decline 
just as observation shows that it does. If this is the right ex- 
planation, however, for its origin, why is it that the pressure 
so generally the world over corresponds closely with the depth? 
It would seem to the writer that possibly a satisfactory solu- 
tion may be had by agreeing first with Leslie and White that 
the gas has been generated near where found, and the pressure 
primarily was due to the amount generated in proportion to 
the size of the receptacle into which it was forced. As the 
ground is so filled with water, this water in places might act 
as a water valve. If, now, the pressure should become suffi- 
ciently great, it would leap through the water valve and the 
gas left behind would exist under a pressure practically de- 
termined by a column of water, although possibly many times 
