It must seem probable, however, that the greatest advance would take place when those lands where things grow quickest under the influence of heat energy, made available by the presence of sufficiency of moisture, were brought into the world organization. We have seen that the equatorial forests have hitherto remained outside that organization. It was not possible for an early civilization to develop within them; hitherto the growth of vegetation has been found too rapid for men to control. But with the experience and knowledge gained by controlling great organizations, made possible by the use of coal, men are now capable of utilizing other vast stores of energy. In our northern lands we have but one crop a year, and growth takes place comparatively slowly. In the basins of the Amazon and Congo, and on the islands of the East Indies, continuous growth is taking place, and that quickly. Here, then, is an ever-renewed source of energy; is it possible to use it ? A beginning has been made, organiza tion is taking place, the world's supply of rubber comes from these forests ; but this, though of importance, is a small matter, for rubber is not a source of energy, its use only tends to save energy; what we should expect would be that these regions would supply energy directly; whether that energy will be obtained from fuel for burning, which is not likely, or from alcohol distilled from things grown, or in some other way, scarcely matters ; the energy is there and may be utilized.
There are, indeed, two reasons why even the white man, capable of organization, has been prevented from undertaking the organization of those regions. In the first place, the conditions are so very different from those to which white men have been accustomed in the northern lands, that there has been a disinclination to attempt the solution of all the problems, to attempt all the adjustments necessary to live well under them; in other words, it is difficult to get people to change their habits, to change their ways of doing things ; the momentum is too great. Africa and South America were known of long before the lands of the United States and Canada were discovered, but in the latter men might live in ways not greatly different from those to which they were accustomed; while in the others everything is strange, life has to be planned on different lines, so that white men do not go to these lands in any numbers to settle. At the best they wish 'to go in small numbers for a few years, as they go to India.
Thus it is not surprising that so little progress has been made, especially as, in the second place, not only are the conditions different, but they are dangerous to life. The Greeks and the Romans appear to show a lack of virility in their later as compared with their earlier histories : possibly this may be due in part to the results of malaria introduced from warmer lands which they dominated. Whether or not this be so, it is certainly true that diseases unknown in colder lands bring excessive mortality where the temperature is high, a waste of human life with little corresponding saving.
But here there is evidence that progress is being made ; these diseases and their cause have been investigated— in ways which at first sight gave no promise of any alleviation of human suffering, of any hope that energy would be saved—and methods of, at any rate partial, prevention worked out. A generation ago no one would have predicted that this knowledge would have been obtained by studying the habits of insects of various kinds, by collecting and examining them under a microscope ; yet it is true. Diseases have been proved to be carried from one to another by particular kinds of insects, mostly mosquitoes, and these diseases have been greatly reduced or quite stamped out by exterminating the insects that carry them. In Rio Janeiro in 1898 there were 1078 deaths from yellow fever; in 1908 there were only 4. In Havana, between the years 1853 and
1900, the average annual death rate from yellow fever was 754, in 1907 there was only one death from this disease. In 1887, 21,033 persons died of malaria in Italy ; in 1907 the number was 4160. In Ismailia there were 2000 cases in 1902; there were none in 1905. Port Said has also been cleared of malaria.
There has been a saving of energy even when measured in terms of hard cash ; in 1903 malaria cost the Suez Canal 38,200 francs, while in 1908 the cost was less than half that amount. The construction of the Panama Canal itself has been rendered possible by the discovery of the measures necessary to keep down disease ; plague and yellow fever were stamped out, malaria greatly reduced; the death rate among the employees fell from over 40 per 1000 in 1906 to 10'64 per 1000 in 1909—a lower death rate than is found in most towns of the civilized world.
It has indeed been said, " The climate of equatorial lands is not harmful in itself ; all it does is to give you sunstroke if you go out in the heat of the day with inadequate headgear, and to make it difficult to keep awake after lunch. Tuberculosis, rheumatic fever and influenza are absent. . . . Lvoid the tsetse and you will not get sleeping-sickness, the mosquito and you will not get malaria; do not sleep on mud floors or pitch your tent on old encampments where are ticks and bed bugs ; keep rats at a distance, and you will be safe from plague. With care and attention life in the tropics is more free from disease than is that in our temperate but influenza-ridden Palaearctic climate." The advice given may at present be difficult to follow, but it is an advance to know what advice to give ; when it is possible for great numbers to follow this advice and to profit by the results of further knowledge, then man will be able to use and save the vast stores of energy in the equatorial forests, and the Congo and Amazon will no longer flow through unoccupied regions.
And there is yet another possibility : in the hot desert of the Sahara, with clear sky and practic4lly no rain for years at a time, there is no vegetation, and man has not been able to live, but if it could be possible to use directly the energy of solar radiation, which con tinuously from sunrise to sunset batters the land in little less amount than in lower latitudes, another region which is now vacant would be able to support great populations, and would become of extraordinary im portance. Here, on to an area comparable with that occupied by Greater London, is yearly directed as much solar energy as could be produced on complete com bustion by the total amount of coal annually raised in Britain. Experiments have been made with engines which give a high thermal efficiency, but it is too early to say whether or no the first steps which will lead to a great revolution have been taken. This is certain, that the nearer the equator one goes the greater are the potentialities of saving energy; that there are supplies of energy on which we may draw when coal is exhausted, and that sooner or later these supplies of energy will be used. With their usc, if the past is any criterion for the future, there must come an inevitable change in the distribution of mankind—in habits of life, and in all those matters which profoundly influence the course of history. But the effects of this change will be modified by the past history ; the things that have been will continue to be, because they have been.
With this peep into the future, then, we leave the story; is it out of place or out of date to suggest that some " increasing purpose runs " through all the wonderful process whereby things are "made to make themselves "; and that though the mills of God grind slowly they grind exceeding small ?