Oct. 24, 1884.] 



* KNOAAALEDGE * 



333 



expense per ton for mining, carriage, aud so on, according 

 as different parts of the coal-fields were being worked. But 

 for obvious reasons this would not be the place for dealing 

 with the subject in so general or so complete a manner. 

 The sole point I shall here touch on, as bearing on the 

 availability of the various coal-stores, Li the probable depth 

 to which coal-mining operations can be pushed. 



It was held by many, in 1860-64,* that the coal-mines 

 might be worked to a depth far exceeding the greatest which 

 had then been reached. " The difficulties in the way of deep 

 mining," wrote Mr. Leonard Lemoran, Surveyor of Mines, 

 " are mere questions of cost. It is important to notice 

 that the assumption of 4,000 feet as the greatest depth to 

 which coal can be worked, on account of the increase of tem- 

 perature is purely voluntary. The increase has been calcu- 

 lated at a rate for which there is no authority ; and whOe 

 we are saying our coal-beds cannot be worked below 

 4,000 ft., a colliery in Belgium has nearly approached that 

 depth, and no inconvenience is experienced by the miners." 

 But, unfortunately, this sanguine view has not been sup- 

 ported by recent researches. It will be known to our 

 readers that in 1865 Commissioners were appointed for 

 discussing the whole subject of our coal supply. Among 

 their ranks were several of the most eminent geologists, as 

 well as some of the highest authorities on the practical 

 questions involved in the subject. The question of the 

 possible depth to which our mines could be worked was 

 necessarily one to which the Commissioners were bound to 

 give very close attention ; and we may fairly accept the 

 result of their inquiries as representing the most trust- 

 worthy conclusion which has yet Vjeen reached on this par- 

 ticular point. Now, they stated that, according to the 

 ordinary method of working, the depth at which the tem- 

 perature of the mine would reach blood-heat (or 98° Fahr.) 

 is about 3,000 ft. They expressed a belief that, by the 

 " long-wall " system of working, a depth of 3,420 ft. might 

 be reached before this temperature was attained : but 

 whether this will prove to be the case or not remains to 

 be seen. Now, although the human frame can bear for a 

 while a greater heat than 100° or even 200° Fahr.,! yet it 

 would be impossible to carry on such labours as are 

 required in coal-mining, at a higher temperature than 

 blood-heat, without great suffering and the loss of many 

 lives. 



Accordingly, although before the Commissioners began 

 their labours, the total quantity of available coal in Great 

 Britain was reckoned at 200,000,000,000 of tons, it is now 

 generally admitted that, so far as known coal-fields are 

 concerned, the quantity probably available must be reckoned 

 at something less than 150,000,000 000 of tons. The Com- 

 missioners themselves found that in 1871 he had " an 

 aggregate of 146,480,000,000 of tons, which may be reason- 

 ably expected to be available for use." 



It will be observed that this quantity is about a forty- 

 eighth part of the quantity probably available throughout 

 the whole world ; so that Great Britain possesses for her 

 area a singularly large supply of the mineral. 



Yet the consumption of coals in this country is so enor- 

 mous that, although we are thus exceptionally well 

 supplied, statisticians have already begun to look with 

 anxiety upon the rapid exhaustion of our stores. 



* This essay, as originally written, appeared in 1872, bnt it has, 

 of course, been modified considerably. 



t Brewster mentions that Chantrey's workmen used to enter the 

 furnace which the sculptor employed in drying his moulds when 

 the temperature was as high as 340", " walkiiag over the floor with 

 wooden clogs, which are, of course, charred on the surface." 

 Chantrey himself and five or six friends stayed for two minutes in 

 the furnace, bringing out a thermometer which stood at 320°. 



The questions at issue are exceediogly simple. Let 

 it be granted that our total available supply amounts 

 to 150,000,000,000 of tons. Then at the rate of con- 

 sumption in 1872, amounting nearly to 120,000,000 tons 

 per annum, this supply would last the nation 1,250 years. 

 But large as our consumption is, it is not the actual rate 

 which is alarming, but the annual increase of rate. Year 

 by year our consumption is increasing. In 1860-64 it was 

 under 84,000,000 tons, and the average rate of increase 

 during the next ten years was more than 3,500,000 tons. 

 Taking it at only 3,000,000, the supply, as estimated in 

 1872, would not last 280 years. For the increase at the 

 supposed rate would, in 280 years, be no less than 

 840,000,000 tons, making a total annual consumption of 

 060,000,000. The mean between this and the rate in 1872 

 amounted to 540,000,000 ; and it will be found that 280 

 times 540 is greater than 150,000. 



But startling as is the theory that our coal-supply will 

 be completely exhausted in less than 270 years from 1884 

 — a period corresponding to that between the commence- 

 ments of the reigns of Elizabeth and our present Queen — 

 there are those who entertain an even more disheartening 

 view. According to them it is not even the rate of increase 

 of the annual consumption which forms the most threatening 

 feature of the case, but the rapidity with which this rate of 

 increase is itself increasing. 



Thus Mr. Hull, dealing with the coal supply as I have 

 just done, took 1,500,000 tons for the average annual in- 

 crease (admittedly, however, a low estimate). We have 

 seen that the average annual increase ten or twelve years 

 ago could not be set at less than 3,500,000. How, if in 

 twenty years the average annual increase should have risen 

 to ."1,000,000 1 in half a century later to 10,000,0001 and 

 so on. It is clear, at least, that if changes such as these 

 take place in the rate of increase, we have greatly over- 

 estimated in the above calculations the probable duration 

 of our coal-supply. 



Mr. Stanley Jevons, in discussing the subject in 1863, 

 took the increase of increase into account with very 

 startling results. He said : " We, of course, regard not 

 the average annual arithmetical increase of coal consump- 

 tion, but the average rate per cent, of increase, which is 

 found by computation to be 3-26." Now, to illustrate the 

 difference between this method and the other, we shall not 

 take the actual figures, which are inconvenient for ready 

 computation. Instead of doing so, we shall compare two 

 simple progressions. One is the series 100, 110, 120, 130, 

 140, 150, and so on, increasing by ten at each step ; the 

 other is a progression increasing at the rate of ten per 

 cent, and runs thus: — 100, 110, 121, 133 (not counting 

 fractions), 146, 161, and so on. It will be observed that 

 the corresponding terms of the two series differ more 

 and more from each other as we proceed : the difference 

 is but one at the third term, and amounts to eleven at 

 the sixth. It wUl be found to increase marvellously 

 with a few more steps. Now, the difference between 

 Mr. Stanley Jevons' method and Mr. Hull's is precisely 

 analogous ; only that whereas the rate per cent, just con- 

 sidered is tin, it is in the actual case about three and a 

 quarter. 



The fact really is, that the rate of increase corresponds 

 precisely, in one case, to that of a capital of 120,000,000 

 sterling, increased each year by simple interest at the rate 

 of 3| per cent., while, in Mr. Jevons' method of calcula- 

 tion, the increase is as that of a capital of 120,000,000 

 sterling, increased by compound interest at the rate of 3^ 

 per cent, per annum. To give an idea of the actual differ- 

 ence as respects the consumption at some distant epoch, let 

 us take the year 1950. Then, according to the former 



