G. H. KNIBBS. XXXIII. 
irrigation is gravitational, sometimes does not pay when it 
involves pumping. If economic developments take place 
on ascale justified by gravitational irrigation from artesian 
sources, and the condition should change, the economic 
disaster may of course become serious, even though there 
is stilla sure supply. This suggests the— 
4. Necessity for scientific investigation.—Should the 
artesian waters be drawn upon to such an extent as to 
convert the whole artesian area to the sub-artesian con- 
dition, wells originally flowing freely becoming practically 
useless, we are surely reverting to the original condition 
of aridity. Consider for a moment how this may arise. 
Professor Gregory’s theory as an hydraulic explanation 
may, we think, be dismissed, because even though gaseous 
pressure and thermal expansion be contributory factors, 
they would, if his theory were correct, also work in some 
measure against the hydrostatic head at the region of 
intake in a manner practically equivalent to raising the 
hydrostatic (and also hydraulic) head. And then the real 
question to deal with would be this, viz.:—‘ Is the pressure- 
head due to entrance of water in the region of intake the 
work of centuries, or of only a short period?’ ‘Is the 
draught on the artesian supply appreciably greater than 
the yearly increase ?’ 
Let us suppose that the pressure-head, as it stands, is 
very great, being the work of centuries of accumulation 5 
then that head, being the cause of the velocity of flow, 
will be maintained so long as the total flow from the 
artesian ivells is not greater than the yearly increment 
in the area of intake, but if the total flow exceed the 
intake supply we are on the way to inevitable disaster. 
If it were possible to maintain Professor Gregory’s view, 
the case would be even still more serious, but without 
adopting his view the matter is sufficiently serious to call 
_for public attention. 
5—July 20, 1903, | 
