XXVIII. HYDRAULIC ASPECT OF THE ARTESIAN PROBLEM. mse 
(2) The resistances in the stratum itself, especially at points 
near the bore. 
The former can be estimated for a new pipe, but hardly 
for an old one, and it is to be expected that the rate of. 
artesian flow will always shew some reduction, merely 
from the pipe becoming less smooth through corrosion, 
deposit, etc. 
This can be roughly estimated, but resistances in the 
stratum must always be somewhat conjectural. Hor they 
depend upon the size of the grains, the porosity, and the 
thickness of the stratum. This leads us to the consider- 
ation or the :—— 
3. Unknown factors in the problem.—As an hydraulic 
problem the flow is calculable a priori only when the con- 
ditions can be definitely specified. But with both the 
thickness, the coarseness, and the porosity of the stratum 
all uncertain or non-uniform, the problem does not submit 
to definite treatment. There is according to Professor 
Gregory, another element which must be taken into account 
viz., the earth’s internal heat, which he assumes to increase 
at the rate of about 1° C. for about every 100 feet of 
descent, an amount which appears to vary greatly from 
place to place and is rarely as rapid as this. | | 
The following increases of temperature have been 
recorded, in each case for 1° Centigrade : 
Feet. 
Cremorne Bore ... ... 144 Journ. Roy. Soc. N.S.W., xxvi1., 464, 1893. 
_ Metropolitan Colliery ... 140 ~ (T. W. E. David and 
General value? ... las A E. F. Pittman) 
Sydney Raibon Colliery 163 ss XXXIII., 223, 1899. 
Schladebach Bore, Prussia 117 3 (J. L. C. Rae, 
Astley Colliery, Dukenfield 130 . E. F. Pittman, 
Ashton Moss Colliery, 139 and 
Manchester T.,W. E. David) 
Dukenfield Colliery _... 149 Ap ” 
St. Gothard Tunnel _.... 147 SAS ” 
Lansells’ Mine, Bendigo, 200 55 ” 
Victoria 
Przibram Silver Mine, 227 as RS 
Bohemia 
Calumet and Hecla Lode 401 tie ” 
Lake Superior, U.S.A. 
