liv REPORT—1863. 
which, at the present rate of consumption, would be exhausted in 930 years, 
but, with a continued yearly increase of 2? millions of tons, would only 
last 212 years. It is clear that long before complete exhaustion takes place, 
England will have ceased to be a coal-producing country on an extensive 
scale. Other nations, and especially the United States of America, which 
possess coal-fields 37 times more extensive than ours, will then be work- 
ing more accessible beds at a smaller cost, and will be able to displace the 
English coal from every market. The question is, not how long our coal 
will endure before absolute exhaustion is effected, but how long will those 
particular coal-seams last which yield coal of a quality and at a price to 
enable this country to maintain her present supremacy in manufacturing 
industry. So far as this particular district is concerned, it is generally 
admitted that 200 years will be sufficient to exhaust the principal seams 
even at the present rate of working. If the production should continue 
to increase as it is now doing, the duration of those seams will not reach half 
that period. How the case may stand in other coal-mining districts I 
have not the means of ascertaining; but as the best and most accessible 
coal will always be worked in preference to any other, I fear the same rapid 
exhaustion of our most valuable seams is everywhere taking place. Were 
we reaping the full advantage of all the coal we burnt, no objection could 
be made to the largeness of the quantity, but we are using it wastefully and 
extravagantly in all its applications. It is probable that fully one-fourth 
of the entire quantity of coal raised from our mines is used in the pro- 
duction of heat for motive power; but, much as we are in the habit of 
admiring the powers of the steam-engine, our present knowledge of the 
mechanical energy of heat shows that we realize in that engine only a small 
part of the thermic effect of the fuel. That a pound of coal should, in our 
best engines, produce an effect equal to raising a weight of a million pounds 
a foot high, is a result which bears the character of the marvellous, and 
seems to defy all further improvement. Yet the investigations of recent 
years have demonstrated the fact that the mechanical energy resident in a 
pound of coal, and liberated by its combustion, is capable of raising to the 
same height 10 times that weight. But although the power of our most 
economical steam-engines has reached, or perhaps somewhat exceeded, the 
limit of a million pounds raised a foot high per lb. of coal, yet, if we take the 
average effect obtained from steam-engines of the various constructions now 
in use, we shall not be justified in assuming it at more than one-third of 
that amount. It follows therefore that the average quantity of coal which 
we expend in realizing a given effect by means of the steam-engine is about 
30 times greater than would be requisite with an absolutely perfect heat- 
engine. 
The causes which render the application of heat so uneconomic in the 
steam-engine have been brought to light by the discovery of the dynamical 
theory of heat ; and it now remains for mechanicians, guided by the light 
they have thus received, to devise improved practical methods of converting 
the heat of combustion into available power. 
Engines in which the motive power is excited by the communication of 
heat to fluids already existing in the aériform condition, as in those of 
Stirling, Ericson, and Siemens, promise to afford results greatly superior to 
those obtained from the steam-engine. They are all based upon the principle 
of employing fuel to generate sensible heat, to the exclusion of latent heat, 
which is only another name for heat which has taken the form of unprofitable 
motion amongst the particles of the fluid to which it is applied. They also 
