September 25j 1914] 



SCIENCE 



439 



extent as the unbroken surface of the 

 prairie ; on the other hand, it is more reten- 

 tive at once of moisture and of the rays of 

 the sun. The result is that the wheat zone 

 has moved further north, and that the in- 

 tervention of man has, at any rate for agri- 

 cultural purposes, made the climate of the 

 great Canadian northwest perceptibly 

 more favorable than it was. In Lord 

 Strathcona's view, there was some change 

 even before the settlers came in, as soon as 

 the rails and telegraph lines of the Ca- 

 nadian Pacific Railway were laid. He told 

 me that in carrying the line across a desert 

 belt it was found that, within measurable 

 distance of the rail and the telegraph line, 

 there was a distinct increase of dew and 

 moisttire. I must leave it to men of science 

 to say whether this was the result of some 

 electrical or other force, or whether what 

 was observed was due simply to a wet cycle 

 coinciding with the laying of the rails and 

 the erection of the wires. I am told that it 

 is probably a coincidence of this kind, 

 which accounts for the fact that in the 

 neighborhood of the Assouan dam there is 

 at present a small annual rainfall, whereas 

 in past years the locality was rainless. 

 Reference has already been made to the ef- 

 fect of cultivation in the Kalahari Desert 

 in increasing the storage of moisture in 

 the soil. But it is when we come to the 

 division between healthy and unhealthy 

 climates that the effect of science upon cli- 

 mate is most clearly seen. The great re- 

 searches of Ross, Manson and many other 

 men of science, British and foreign alike, 

 who have traced malaria and yellow fever 

 back to the mosquito, and assured the pre- 

 vention and gradual extirpation of tropical 

 diseases, bid fair to revolutionize climatic 

 control. Note, however, that in our peni- 

 tent desire to preserve the wild fauna of 

 the earth we are also establishing pre- 

 serves for mosquitoes, trypanosomes and 

 the tsetse fly. 



Nowhere have the triumphs of medical 

 science been more conspicuous than where 

 engineers have performed their greatest 

 feats. De Lesseps decided that Ismailia 

 should be the headquarters of the Suez 

 Canal, but the prevalence of malaria made 

 it necessary to transfer the headquarters to 

 Port Said. In 1886 there were 2,300 cases 

 of malaria at Ismailia; in 1900 almost ex- 

 actly the same number. In 1901 Sir Ron- 

 ald Ross was called in to advise; in 1906 

 there were no fresh eases, and the malaria 

 has been stamped out. De Lessep 's attempt 

 to construct the Panama Canal was de- 

 feated largely, if not mainly, by the fright- 

 ful death-rate among the laborers; 50,000 

 lives are said to have been lost, the result 

 of malaria and yellow fever. When the 

 Americans took up the enterprise they 

 started with sending in doctors and sanitary 

 experts, and the result of splendid medical 

 skill and sanitary administration was that 

 malaria and yellow fever were practically 

 killed out. The Panama Canal is a glorious 

 creation of medical as well as of engineer- 

 ing science, and this change of climate has 

 been mainly due to reclamation of pools 

 and swamps, and to cutting down bush, for 

 even the virtuous trees, under some condi- 

 tions, conduce to malaria. Man is a geo- 

 graphical agency, and in no respect more 

 than in the effect of his handiwork on cli- 

 mate, for climate determines products, hu- 

 man and others. Science is deciding that 

 animal pests shall be extirpated in the 

 tropics, and that there shall be no climates 

 which shall be barred to white men on the 

 ground of danger of infection from trop- 

 ical diseases. 



If we turn to products, it is almost super- 

 fluous to give illustrations of the changes 

 wrought by man. As the incoming white 

 man has in many places supplanted the 

 colored aboriginal, so the plants and the 

 living creatures brought in by the white 

 man have in many cases, as you know well, 



