438 



SCIENCE 



[N. S. Vol. XL. No. 1030 



by constructing a dam on the Blue Nile at 

 Sennaar and cutting a canal 100 miles long 

 which, if I understand right, will join the 

 White Nile thirty miles south of Khartoum. 



With the advance of science, with the 

 growing pressure of population on the sur- 

 face of the earth, forcing on reclamation 

 as a necessity for life, is it too much to con- 

 template that human agency in the coming 

 time will largely obliterate the deserts 

 which now appear on our maps ? It is for 

 the young peoples of the British Empire 

 to take a lead in — to quote a phrase from 

 Lord Durham's great report — "the war 

 with the wilderness," and the great feat of 

 carrying water for 350 miles to Kalgoor- 

 lie, in the very heart of the wilderness, 

 shows that Australians are second to none 

 in the ranks of this war. 



It is a commonplace that rivers do not 

 make good boundaries because they are 

 easy to cross by boat or bridge. Pascal 

 says of them that they are "des chemins 

 qui marchent" (roads that move), and we 

 have seen how these roads have been and 

 are being improved by man. "Rivers 

 unite," says Miss Semple; and again, 

 "Rivers may serve as political lines of 

 demarcation, and therefore fix political 

 frontiers, but they can never take the place 

 of natural boundaries. All the same, in 

 old times, at any rate, rivers were very ap- 

 preciable dividing lines, and when you get 

 back to something like barbarism, that is 

 to say in time of war, it is realized how 

 powerful a barrier is a river. Taking, 

 then, rivers as in some sort natural boun- 

 daries, or treating them only as political 

 boundaries, the point which I wish to em- 

 phasize is that they are becoming boun- 

 daries which, with modern scientific appli- 

 ances, may be shifted at the will of man. 

 In the days to come the diversion of rivers 

 may become the diversion of a new race of 

 despotic rulers with infinitely greater 



power to carry out their will or their 

 whim than the Pharaohs possessed when 

 they built the Pyramids. You in Australia 

 know how thorny a question is that of the 

 control of the Murray and its tributaries. 

 There are waterways conventions between 

 Canada and the United States. Security 

 for the headwaters of the Nile was, and is, 

 a prime necessity for the Sudan and 

 Egypt. The Euphrates is being turned 

 from one channel into another. What in- 

 finite possibilities of political and geo- 

 graphical complications does man's grow- 

 ing control over the flow of rivers present ! 



Thus I have given you four kinds of bar- 

 riers or divisions set by nature upon the 

 face of the earth — mountains, forests, des- 

 erts, rivers. The first, the mountains, man 

 can not remove, but he can and he does go 

 through them to save the trouble and diffi- 

 culty of going over them. The second, the 

 forests, he has largely cleared away alto- 

 gether. The third, the deserts, he is begin- 

 ning to treat like the forests. The fourth, 

 the rivers, he is beginning to shift when it 

 suits his purpose and to regulate their flow 

 at will. 



I turn to climate. Climates are hot or 

 cold, wet or dry, healthy or unhealthy. 

 Here our old friends the trees have much 

 to say. Climates beyond dispute become 

 at once hotter and colder when trees have 

 been cut down and the face of the earth 

 has been laid bare; they become dryer or 

 moister according as trees are destroyed or 

 trees are planted and hold the moisture; 

 the cutting and planting of timber affects 

 either one way or the other the health of a 

 district. The tilling of the soil modifies the 

 climate. This has been the ease, according 

 to general opinion, in the northwest of 

 Canada, though I have not been able to se- 

 cure any official statistics on the subject. 

 In winter time broken or ploughed land 

 does not hold the snow and ice to the same 



