THE EYOLUTIOX OF XATIOXS 177 



merit and importance ont of proportion, both to the actual use and to 

 the greatest possible productivity of the soil in each of the national 

 areas mentioned. These eases may be taken as typical of a particular 

 stage of development into which some of the nations of to-day have 

 -:;=5ed naturally, but which the younger nations of the present, as 

 Argentine, Brazil or Canada, can only approach. The stage of develop- 

 ment represented by Britain, Germany or Japan depends on the tem- 

 porary operation of the sixth and seventh physical factors — the pos- 

 session of potential energy and useful minerals. Later s:;res, as will 

 be indicated, may very likely bring once more into prominence the in- 

 fluence of the productivity of the soil in the national territory itself. 



Potential Energy. — Under the head of potential energy may be 

 grouped all the natural means of developing mechanical power — coal, 

 ■ nrnnincr water, wind and even the direct ravs of the sun. Modern 

 civilization is inseparably associated with the use of two things de- 

 pendent on potential energy in one form or another: first, the use of 

 heat other than that received direct from the sun : and second, the use 

 of machinery which requires mechanical power either for its making or 

 in its operation. But since heat for any purpose may be secured from 

 mechanical power through the medium of electricity, both needs, for 

 machinery and for heat, hinge on the one question of some single form 

 of potential energy. Coal until recently, at least, has been the one im- 

 portant form of potential energy, for the reason that it furnishes heat 

 directly or supplies power through the medium of steam. These quali- 

 ties coupled with the possibility of transporting the latent energy to the 

 desired place of utilization, have enabled coal to play perhaps a dis- 

 proportionate part in directing national development, but its effect may, 

 with some qualification, be taken as indicating the part which mechan- 

 ical energy, in any form, can play in national evolution. 



The value of mechanical power to a nation is best expressed in terms 

 of its equivalent in either animal or man power. One horse power, me- 

 chanical energy, may be taken as the equivalent of the power of two 

 average horses or of ten men for a working day of ten hours. A mod- 

 ern steam engine requires not over 2 to 5 pounds of coal for the develop- 

 ment of one horse power per hour — a gas engine requires even less — 

 hence a very conservative calculation gives fifty horse power for a 

 working day of ten hours from a single ton of coal. In other words, a 

 ton of coal does in a day the work of at least one hundred horses or of 

 five hundred men. Therefore, one man engaged in mining two tons of 

 coal per day, is producing through the expenditure of one man-power 

 the energy equivalent of a population of 1,000 working men. Calcu- 

 lated on the same basis of values, 80,000 tons of coal produced daily 

 for 300 working days in the year — 2i,000,000 tons annually — are, in 

 the power they afford, equal to the full energy of a working force 



