vii REPORT—1863. 
observed temperature of the strata at this depth agrees pretty closely with 
what has been ascertained in other localities, and shows that the increase 
takes place at the rate of 1° Fahr. to about 60 feet of depth. Assuming the 
temperature of subterranean fusion to be 3000°, and that the increase of heat 
at greater depths continues uniform (which, however, is by no means certain), 
the thickness of the film which separates us from the fiery ocean beneath 
will be about thirty-four miles—a thickness which may be fairly repre- 
sented by the skin of a peach taken in relation to the body of the fruit which 
it covers. The depth of 4000 feet, which has been assumed as the limit at 
which coal could be worked, would probably be attended by an increase 
of heat exceeding the powers of human endurance. In the Monkwearmouth 
colliery, which is less than half that depth, the temperature of the air in the 
workings is about 84° Fahr., which is considered to be nearly as high as is 
consistent with the great bodily exertion necessary in the operation of mining. 
The computations therefore of the duration of coal would probably require a 
considerable reduction in consequence of too great a depth being assumed as 
practicable. 
At the last Meeting of the British Association in this town, the import- 
ance of establishing an office for mining records was brought under the notice 
of the Council by Mr. Sopwith, and measures were taken which resulted in 
the formation of the present Mining Records Office. The British Association 
may congratulate itself upon having thus been instrumental in establishing an 
office in which plans of abandoned mines are preserved for the information of 
those who, at a future period, may be disposed to incur the expense of bringing 
those mines again into operation. But more than this is required. Many of 
the inferior seams of coal can be profitably worked only in conjunction with 
those of superior quality, and they will be entirely lost if neglected until the 
choicer beds be exhausted. Although coal is private property, its duration 
is a national question, and Government interference would be justified: to 
enforce such modes of working as the national interests demand. - But to 
enable Government to exercise any supervision and control, a complete 
mining suryey of all our coal-fields should be made, and full plans, sections, 
and reports lodged at the Mining Records Office for the information of the 
legislature and of the public in general. 
- Before dismissing the subject of coal, it may be proper to notice the recent 
discovery by Berthelot of a new form of carburetted hydrogen possessing 
twice the illuminating power of ordinary coal-gas. Berthelot succeeded in 
procuring this gas by passing hydrogen between the carbon electrodes of a 
powerful battery. Dr. Odling has since shown that the same gas may be 
produced by mixing carbonic oxide with an equal volume of light carbu- 
retted hydrogen and exposing the mixture in a porcelain tube to an intense 
heat. Still more recently, Mr. Siemens has detected the same gas in the 
highly heated regenerators of his furnaces, and there is now every reason to 
believe that the new gas will become practically available for illuminating- 
purposes. Thus it is that discoveries which in the first instance interest 
the philosopher only almost invariably initiate a rapid series of steps leading 
to results of great practical importance to mankind. 
In the course of the preceding observations I have had occasion to speak of 
the sun as the great source of motive power on our earth, and I must not omit 
to refer to recent discoveries connected with that most glorious body. Of all 
the results which science has produced within the last few years, none has 
been more unexpected than that by which we are enabled to test the materials 
of which the sun is made, and prove their identity, in part at least, with those 
