174 Proceedings of the Boyal Physical Society. 
dicular depth, and not influenced by the size, or shape, or 
position of the containing vessel." These two laws are 
practically exhibited in the Accumulator in the following 
fashion : — A reservoir of water is placed at a convenient 
height from the power on which it is proposed to operate. 
A heavy w^eight is made to press upon the reservoir, and a 
communication is made with the engine which is to apply 
the power gained, by means of a tube of very small dia- 
meter. It is found that the power thus practically gained 
is equal not to that represented by the pressure of the weight 
upon the reservoir, but to that pressure j)lus the pressure of 
an imaginary reservoir equal in depth to that of the connect- 
ing tube from the reservoir to the engine. 
If, then, natural reservoirs of water in the rocks have a 
mass of superincumbent strata pressing on them, and a com- 
munication be opened downwards by a narrow outlet, the 
pressure at the spot where the outlet terminates must be 
governed by the same laws. That such forces actually exist 
is undoubted. And they may be a possible cause of such 
natural phenomena as the reappearance of rivers which have 
flowed for some time in a subterranean channel, the outburst 
of fresh-water springs in the sea, or in places where no de- 
clivity is known suflicient to account for their outburst on a 
plain. 
When, however, we estimate the water which is absorbed 
by porous strata as existing in a natural reservoir, and 
pressed down by impervious strata above, this hydraulic 
problem will have a much wider geological application. It 
will likewise require nice discrimination to determine how 
much the faults and fissures of the strata are due to this 
cause, and in what degree to other physical forces. 
The amount of rain-fall is quite sufficient to afford the 
means of such a power in almost any situation. It has been 
calculated that every inch in the depth of rain falling upon 
a single acre is equal to one hundred tons, so that there falls 
3000 tons- weight of rain annually upon every acre, or, daily, 
f|-^ tons. The rain-fall varies at certain seasons of the 
year. Mr Bailey Denton states that, at Hinxworth, the 
discharge from the open lands amounted, in January and 
