DISCOVERY 



131 



glass or the water vapour acts as a screen to them. The 

 atmosphere in this case is just a blanket like the roof 

 of a greenhouse, with all the benefits which naturally 

 accrue from it. This is the main reason why moist 

 climates are so much more equable than dry ones. In 

 a desert the day temperature often rises to 120 degrees ' 

 or even 140 degrees Fahrenheit in the shade, while at 

 night it may fall to below freezing-point. In a moist 

 climate in the same latitude the daily range will be 

 perhaps from 80 to 85 degrees shade temperature in 

 the day, and 65 to 70 degrees at night. The hotter the 

 climate the more marked are these effects. In the 

 moist climate of Bengal, in the forested parts, the 

 thermometer scarcely ever reaches 90 degrees in the 

 shade, whilst at night it is rarely below 80 degrees. In 

 the same latitude in Bikaneer Desert or in the Sahara, 

 the temperatures have a diurnal range of perhaps 

 70 degrees or 80 degrees instead of 10 degrees, and this 

 is entirely due to the presence of moisture in the air. 

 It follows, then, that the hotter the climate the more 

 careful man should be to preserve his trees, but 

 unfortunately exactly the reverse is usually the case, 

 either from ignorance, want of fuel, or shortness of 

 pasture. 



Damage by Animals 



It usually happens that when a country is deforested, 

 goats and camels are turned on to the land. Any live 

 roots are speedily grazed out of existence, seedlings are 

 destroyed, and the humus pulverised and scattered. 

 Then the replanting is a difficult and expensive job. 

 If it happens to be a country without summer rain, such 

 as Sicily and the Mediterranean shores have become 

 owing to the influence of the Sahara, no seedling can 

 get its roots deep enough in one season to stand the 

 desiccating effect of the summer drought, which may 

 penetrate a couple of feet. Only the planting of 

 young trees of larger growth can then be effective, at, of 

 course, a much enhanced cost. The downward grade 

 is cumulative ; the longer the replanting it put off, the 

 more difficult and expensive does it become. 



One of the effects of deforestation is to accentuate 

 the drying due to atmospheric circulation acting on 

 the present distribution of water and land on our globe. 

 The result is the menacing increase in the desert areas 

 of the earth. 



Only lately it has been found that, notwithstanding 

 all that we have done in Egypt with dams and canals, 

 there is now a shortage of water ! The Government has 

 sent an expedition to examine the sources of the Nile, 

 and to decide if anything can be done to increase and 

 conserve them. 



Equatorial rains are usually very heavy, but they 

 have a long way to run to reach Egj'pt. The loss by 

 evaporation and by seepage on the way from Abyssinia 



is very great. As the countries through which the Nile 

 runs gradually dry under the malign influence of the 

 Sahara, so the level of the subterranean reservoir 

 lowers, and the more is the loss to the river flowing 

 above it. Once upon a time, when a race of palaeolithic 

 savages lived in Egypt, that country was blessed with 

 abundant rainfall and luxuriant vegetation ; that is 

 admitted by all geologists and archaeologists. It is 

 easily seen to have been the case by the valleys and 

 guUeys cut by water which run down to the Nile, but 

 are now dry. The famous Valley of the Kings, where 

 Lord Carnarvon's wonderful treasure tomb has been 

 found, is a case in point. There a short stream, a 

 few miles in length, has been so full and strong that it 

 has been able to cut a channel at least two hundred 

 feet deep in hard limestone rocks, leaving beetling 

 precipices that once bordered the current, but now 

 afford starting places for the tomb galleries. 



It is unfortunate that the animals that man domesti- 

 cated in hot countries should have been the worst 

 possible in abetting him in the destruction of trees — ■ 

 camels, donkeys, goats, all eat branches and leaves of 

 growing trees as high as they can reach. What chance 

 has a young tree of growing up ? The tall old ones die 

 and are not replaced, so deforestation goes on apace, 

 man in his ignorance being his own enemy. 



Not Yet Too Late 



Our task is to make our earth comfortably habitable 

 for the largest number of human beings it can hold. 

 To do this, it is of the greatest importance to cover the 

 soil where possible with a canopy of leaves, so as to 

 regulate the gradual distribution of the rain that falls. 

 It is not yet too late for man to begin covering the waste 

 places of the earth with trees. Probably, if left to 

 themselves, many of them would regain their forests. 

 In former ages, when all vegetation had been destroyed 

 by cold and ice in glacial periods of continental ice, the 

 forests regrew themselves time after time. Man can 

 accelerate the process as was done by the late Lord 

 Armstrong, who planted over three million trees with 

 magnificent enterprise, when he was over fifty years of 

 age. He lived to see many of them one hundred feet 

 high and four feet in diameter. He proved that, by 

 scouring the arboretums of the earth, it was possible 

 to obtain much finer results than by trusting to the local 

 growths. 



A great deal can be done in conserving our growth, as 

 is shown by the fine foresight of a certain newspaper. 

 It was found that trees of thirty years' growth were 

 suitable for paper, and that an area of so many acres 

 was required for a year. Thirty times this area was 

 bought in Newfoundland, one-thirtieth of it is cut every 

 year and at once replanted. The water of a lake and 

 waterfall is used to turn the wood into pulp suitable 



