XLIV. HYDRAULIC ASPECT OF THE ARTESIAN PROBLEM. . 
perhaps twice this. If such a deduction be correct, it is 
evident that one might expect to find the pressure or efflux 
in any artesian well correspondingly variable. Again, it 
may be observed that fall of barometric pressure will 
destroy the equilibrium of the contained air in rocks and 
soil and act virtually as an increase of hydrostatic pressure. 
Thus both increase and diminution of pressure, tend to 
produce identical results. But in the one case, viz., the 
former, the action is practically instantaneous, in the other 
it is decidedly otherwise ; so that the actual phenomenon, 
the resultant of both, is not easy of exact analysis, inas- 
much as the lag in the effect of low pressure must be ascer- 
tained. Where the conditions are definite, the barometric 
influence is clearly exhibited, and there are a number of 
experimental results shewing this to be the case. 
11. Investigation of fluctuation of fiow.—There is no 
doubt whatever about the fact that the movement of 
centres of high and low pressure across the artesian area, 
cause a variation of flow. A perfect determination of 
the way in which these act will not perhaps be easy, but 
sufficient data will certainly make it possible to deduce the 
real theory of variation of efflux or pressure. Some observ- 
ations already exist, but for subartesian wells only so far 
as lam aware. It is very easy to get records for any type 
of well, flowing or otherwise, by connecting one end of a 
small pipe with the artesian bore, some distance downward 
from the top of the bore and the other end with a mano- 
meter, or better still a self-registering-pressure gauge. A 
record of pressure variation can in this way be obtained. 
It is very desirable of course that these should be supple- 
mented with measurements of the absolute volume of flow. 
Besides large variations of pressure, there are also smaller 
oscillations of short period, the cause of which is not yet 
explained. | 
