“In working through the statistical returns of the progressive increase of population, of steam power employed, and of production of iron and steel, &c., I find that our necessities increase at a rate of not less than 8 per cent. per annum, whereas our coal consumption increases only at the rate of 4 per cent., showing that the balance of 4 per cent. is met by what may be called our ‘intellectual progress.’ Now, considering the enormous margin for improvement before us, I contend that we should not be satisfied with this rate of intellectual progress, involving as it does an annual deficit of four million tons to be met by increased coal production, but that we should bring our intellectual progress up to the rate of our industrial progress, by which means we should make the coal production nearly a constant quantity for several generations to come.” One of the direct results of this lecture, which was read and warmly commended by some of the most eminent men of the time, was that Dr. Siemens was consulted by Mr. Mundella in reference to parliamentary action by the Board of Trade in regard to the coal question. In 1874 he received the Albert Gold Medal from the Society of Arts “for his researches in connection with the laws of heat, and for services rendered by him in the economisation of fuel in its various applications to manufactures and the arts,” and in 1877 he devoted nearly the whole of his address to the Iron and Steel Institute, of which he was then President, to the same subject, in which, as regards the probable duration of our coal supply, he had been for some time engaged in a controversy with the late Professor Jevons, maintaining that “the ratio of increase of population and output of manufactured goods would be nearly balanced for many years to come by the further introduction of economical processes, and that our annual production would remain substantially the same within that period, which would probably be a period of comparatively cheap coal.”