176 
type ; diving apparatus, which has been the means of 
saving a mine from almost irretrievable destruction. Time, 
however, will not permit reference to these on the present 
occasion. But the writer may possibly be permitted to call 
attention to an improved theodolite, for Mine Surveying, 
&;c., which he had the honour of bringing before the Mining 
and Geological section of the South Kensington Museum, 
on a recent occasion. 
(8) PROBABLE FUTURE OF DEEP MINING. 
Having endeavoured to present to you a record of the 
achievements in mining engineering up to the present time, 
our attention may now be profitably directed to the inquiry 
as to the probable limit in depth that coal mining may 
reach. This subject is one that has been touched on by Mr. 
Hull, in his " Coal Fields of Great Britain," and recently 
very ably treated by Mr. Bainbridge, in a paper read by 
him before the Institute of Civil Engineers, and is also 
discussed in the Report of the Royal Coal Commission. It 
is not necessary, nor will time permit, of a detailed recapitu- 
lation of the investigations that have been made on this 
subject, and it is proposed to confine attention to the 
evidence on the two following points : — First, depth at 
which coal may ultimately be worked, and adequate venti- 
lation obtained ; second, cost of production at such increased 
depths. 
By reason of the improved methods of mining, the cost 
of production, down to a depth of 1,000 yards, has not been 
materially increased, or prevented such mines from compet- 
ing, to some extent, with those of shallower depths ; and 
their ventilation has not presented any extraordinary diffi- 
culties to be overcome. In passing from 1,000 yards to 
greater depths, the engineering difficulties increase, but not 
to such an extent as to interfere with its practicabiHty. 
