12 
UNDERGROUND TEMPERATURE. 
‘^Now, although such a chemical process as this, which is very 
improbable to take place in the interior of the earth, is the most 
favourable for the production of heat, still it only caused an 
increase of temperature of i°'35.” We can, therefore, only at- 
tribute the temperature of thermal springs aud geysers to the 
superior temperature of the interior of the earth. Volcanic action 
is a strong argument in support of this view. The enormous 
quantity of molten matter thrown out from their craters tells of a 
heat below, such as would fuse any substance known. But as 
some substances are less fusible than others, it seems reasonable 
to suppose, that there is no hard and fast line between the solid 
and the fused, but that the former merges into the latter. 
To solve the problem of underground temperature, resort has 
been made to mines, bore-holes, and wells ; and from results 
obtained, the datum adopted by the Royal Coal Commission was, t° 
increase for every 6o feet in descent, but I cannot but think, after 
reviewing many observations made, that there is not sufficient 
evidence to warrant the assertion as a fixed datum for calculation. 
In 1867 the British Association appointed a committee to 
investigate this subject, and Prof. Everitt, the able secretary, has 
annually produced valuable reports. When this committee first 
entered upon the field, they had not only to find places for obser- 
vations, but to devise a method, which could only be arrived at by 
experience. To the ordinary reader it may appear a very simple 
thing, but I can assure you there is scarcely any scientific work 
which requires greater care and thought. 
The sinking of shafts has been looked upon as giving exceptional 
facilities for observation. The usual method has been to bore a 
hole in the strata two or three feet deep, at regular distances, say 
50 feet. The hole is bored with an ordinary borer, then filled 
with water, and the thermometer inserted. The time which the 
instrument has been allowed to remain in has ranged from halfian* 
hour to several hours. Observations thus made, would appear at 
