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SCIENCE 



[N. S. Vol. XXXIV. No. 871 



and useless friction. A good gas-engine 

 utilizes more than one third of the total 

 energy in the gaseous fuel ; two thirds are 

 uneeonomically expended. This is a uni- 

 versal proposition; in order to effect the 

 conversion from one form of energy into 

 another, some energy must be expended 

 uneeonomically. If A is the total energy 

 which it is required to convert ; if B is the 

 energy into which it is desired to convert 

 A ■ then a certain amount of energy, G, 

 must be expended to effect the conversion. 

 In short, A^B -{- C. It is eminently de- 

 sirable to keep C, the useless expenditure, 

 as small as possible; it can never equal 

 zero, but it can be made small. The ratio 

 of C to jB (the economic coefficient) should 

 therefore be as large as is attainable. 



The middle of the nineteenth century 

 will always be noted as the beginning of 

 the golden age of science; the epoch when 

 great generalizations were made, of the 

 highest importance on all sides, philosoph- 

 ical, economic and scientific. Carnot, 

 Clausius, Hebnholtz, Julius Robert Mayer 

 abroad, and the Thomsons, Lord Kelvin 

 and his brother James, Rankine, Tait, 

 Joule, Clerk Maxwell and many others at 

 home, laid the foundations on which the 

 splendid structure has been erected. That 

 the latent energy of fuel can be converted 

 into energy of motion by means of the 

 steam engine is what we owe to Newcomen 

 and Watt; that the kinetic energy of the 

 fly-wheel can be transformed into electrical 

 energy was due to Faraday, and to him, 

 too, we are indebted for the reconversion 

 of electrical energy into mechanical work; 

 and it is this power of work which gives us 

 leisure, and which enables a small country 

 like ours to support the population which 

 inhabits it. 



I suppose that it will be generally 

 granted that the commonwealth of Athens 

 attained a high-water mark in literature 



and thought, which has never yet been 

 surpassed. The reason is not difficult to 

 find; a large proportion of its people had 

 ample leisure, due to ample means; they 

 had time to think and time to discuss what 

 they thought. How was this achieved? 

 The answer is simple: each Greek freeman 

 had on an average at least five helots who 

 did his bidding, who worked his mines, 

 looked after his farm, and, in short, saved 

 him from manual labor. Now, we in 

 Britain are much better off ; the population 

 of the British Isles is in round numbers 

 45 millions ; there are consumed in our fac- 

 tories at least 50 million tons of coal annu- 

 ally, and "it is generally agreed that the 

 consumption of coal per indicated horse- 

 power per hour is on an average about 

 5 lb." (Royal Commission on Coal Sup- 

 plies, Part I.) This gives seven million 

 horse-power per year. How many man- 

 power are equal to a horse-power? I have 

 arrived at an estimate thus: A Bhutanese 

 can carry 230 lb. plus his own weight, in 

 all 400 lb., up a hill 4,000 feet high in 

 eight hours; this is equivalent to aboiit 

 one twenty-fifth of a horse-power; seven 

 million horse-power are therefore about 

 175 million man-power. Taking a family 

 as consisting on the average of five persons, 

 our 45 millions would represent nine mil- 

 lion families; and dividing the total man- 

 power by the number of families, we must 

 conclude that each British family has, on 

 the average, nearly twenty "helots" doing 

 his bidding, instead of the five of the 

 Athenian family. We do not appear, how- 

 ever, to have gained more leisure thereby, 

 but it is this that makes it possible for the 

 British Isles to support the population 

 which it does. 



We have in this world of ours only a 

 limited supply of stored-up energy ; in the 

 British Isles a very limited one — namely, 

 our coalfields. The rate at which this sup- 



