244 



NA TURE 



[Jan. 15, 1885 



arithmetical series were below them. In fact, either from 

 a prolonged fluctuation in trade, or from the operation of 

 the cause we are discussing, the outputs for the last six 

 years have not increased so rapidly as the previous 

 numbers would lead us to expect. The outputs for 

 the years 1854-77 are very fairly expressed by a series 

 of which the first term is 6yg and the ratio i'035S, but 

 ahis series makes the last six terms far too high. 



Again the ratio i'03 gives 71 as the first term, and 

 makes all the early terms considerably too high. In 

 short, the fluctuating numbers in Column I. seem to be 

 best expressed by a series of which the first term is 65 '5 

 and the ratio i'o32j ; the outputs calculated from these 

 data are given in Column IV. 



It is easy also to calculate backwards and obtain earlier 

 terms in the same series, thus for 1840 an output of 

 43,000,000 tons is given, and for 1800 one of 11,700,000, 

 instead of Mr. Hull'sconjectureof 36,000,000 and 10,000,000 

 tons respectively. And taking the true output of 

 163,800,000 of tons in 1883 and the ratio ro325, we can 

 calculate the probable output for any future year. Thus 

 for 1901 we obtain 282,000,000 tons instead of 331,000,000 

 as calculated by Prof. Stanley Jevons. Further, a well- 

 known formula gives the sum of any number of terms of 

 the series, or we can calculate in how many years the 

 amount of coal raised will be equal to any given amount, 

 say to the 144,700,000,000 tons remaining i 1 1884. 

 Making the calculation, we find that if the present rate of 

 increase in the consumption of coal of 3t per cent, per 

 annum continues, or, in other words, if our output of coal 

 continues to double every 22 years, our total supply will 

 be exhausted in io5 years from 1884, or about a.d. 1990. 



Of course no one can suppose that our consumption 

 will continue to increase until it comes to a sudden and 

 final end, but only that within a comparatively short 

 period our output of coal must reach a maximum, and 

 then gradually diminish as it becomes more scarce and 

 expensive. 



These calculations, then, seem to force upon us one of 

 four possible conclusions : — Some new source of energy 

 may be found to supply the place of coal ; a larger pro- 

 portion of the energy contained in our coal may be utilised, 

 so that an output as large as the present one may produce 

 a much larger amount of useful work ; coal may be im- 

 ported from other countries to supply our deficiencies ; 

 or lastly, the commerce and manufactures of England 

 may pass into a stationary or retrograde condition. 



Coal is used directly as a source of heat in our domestic 

 fireplaces, as a source of mechanical energy indirectly in 

 our steam- gas- air- and electric-engines, and as a heating 

 and reducing agent in our metallurgical furnaces. A 

 pound of fairly good coal will heat about 13,000 lbs. of 

 water through 1° F., and in an ordinary steam boiler about 

 8000 of these units of heat are utilised, which suffice to 

 turn rather more than 73 lbs. of water at ordinary tem- 

 peratures into steam. But the unit of heat is able to do 

 work to the extent of raising 775'4 lbs. through one foot 

 in opposition to gravity. Hence, by burning one pound 

 of coal, rather over io,ooj,ooo foot-pounds of work may 

 theoretically be obtained. A first-rate steam-engine does 

 effective work to the extent of about one-ninth of the 

 theoretical amount. Hence, in round numbers, a pound 

 of coal will do 1,000,000 foot-pounds of work, or as much 

 work as is done by 32 ordinary men in ascending the 

 202 feet to the top of the Monument. According to 

 Peclet, a pound of average coal contains '804 lb. carbon, 

 ■0519 lb. hydrogen, and '0787 lb. oxygen, and would there- 

 fore theoretically suffice to reduce SJ lbs. of hematite with 

 formation of 5^ lbs. of iron. Any complete substitute for 

 coal must be able to perform each of these three duties 

 of coal. 



It seems improbable that any new source of energy on 

 the large scale will be discovered, though possibly small 

 engines may be driven by some form of explosive, and 



hence tides, winds, and waterfalls alone, have to be con- 

 sidered as substitutes for coal. According to Sir William 

 Thomson, energy in the form of electricity might be con- 

 veyed for 300 miles through a copper rod with a loss of 

 only 20 per cent, from such a waterfall as Niagara, 

 and stored up in secondary batteries for distribution. 

 It is only necessary, without going into details of expense, 

 to point out that we have no monopoly of winds, tides, or 

 torrents, such as we have had of coal, and in fact, were 

 they the sources of energy, we should compete with our 

 neighbours rather at a disadvantage. 



The next point to consider is how far more economical 

 methods of obtaining and using our coal may reduce the 

 output. It has been already pointed out that, as with coal 

 at its present price it is not commercially possible to work 

 seams less than a foot thick, all such coal is wasted. 

 Large quantities of coal also are more or less unavoidably 

 wasted in the processes of cutting and carrying, and it 

 seems as if any great reduction in this amount must be 

 accompanied by a considerable rise in price. 



The uses to which our coal is applied, may, for the pur- 

 poses of this inquiry, be roughly grouped under four 

 herds — mining and metallurgy ; manufactures, an 1 loco- 

 motion on land and sea ; domestic uses, including the 

 supplies of gas and water ; and lastly, for export. Under 

 the first three heads, no doubt, large saving is possible, 

 but it is not likely to be begun except under the pressure 

 of a scarcity of coal, when the high price of the coal 

 will cause the introduction of more expensive and more 

 efficient machinery. 



By far the most important metallurgical operation is the 

 production of iron, which may therefore be taken as an 

 example of the others. In 1788, 7 tons of coal were used 

 per ton of pig-iron produced, which sank to 5 tons about 

 1800. The introduction of the hot blast in 1829 caused a 

 further drop to 3J tons in 1840 ; and that of regenerators 

 in 1857 caused a further fall to 2A tons in 1S75. But the 

 increase in the quantity of iron manufactured renders the 

 actual saving of coal very small. In 1881, 18,300,000 tons 

 of coal were used in making 8,300,000 tons of pig-iron, 

 and a nearly equal amount of coal was required to convert 

 five-eighths of the pig into wrought iron and steel. So 

 that, in all, the iron-works required 34,voo,ooo tens of 

 coal. 



Experience seems to show that, though our best steam- 

 engines give an efficiency of one-ninth, and the efficiency 

 of air- and gas-engines is even higher, except in special 

 circumstances, it is commercially preferable to use less 

 efficient engines ; the saving of coal at present prices 

 being more than compensated for by the higher cost of 

 the better engine. It is possible, however, that in the 

 future electric engines may be used of far greater efficiency 

 than our present steam-engines. On the other hand, the 

 high rates of speed now demanded both for passengers 

 and goods necessitates the consumption of large quantities 

 of coal. Thus on a level railway a ton of load requires 

 a pull of about l6i lbs. to draw it at the rate of 29 miles 

 per hour, while, if the rate be increased to 50 miles per 

 hour, the pull is nearly 33 lbs. Hence th; 13,500 loco- 

 motives in Great Britain will require much more coal to 

 drag the same loads at the higher rate. Cur merchant 

 navy also is being rapidly converted from sailing into steam 

 vessels ; in the 14 years 1866-1879, the number of sailing 

 vessels decreased 5600, while the steamers increased 2200; 

 and the steamers engaged in the foreign trade used in 

 1881 5,200,000 tons of coals, in 1882 5,600,000, and in 

 1883 6,400,000. 



The aggregation of people in towns requires the use of 

 coal for the production of gas or electric lighting, fre- 

 quently for the removal of sewage and refuse, and for the 

 supply of water. Possibly the most wasteful use to which 

 coal is applied is our common domestic fireplace. But it 

 would require an enormous increase in the price of coal 

 to induce the average Englishman to convert his genial, 



