INFLUENCE ON TEMPERATURE. 



129 



June or July, while in the woodless plains of the Ganges the amount of rainfall 

 snclclenly increases from May to June or from June to July. 



The Amazon hasin. — At the present time there are in the basin of the Amazon four 

 stations where observations are made ; this river basin is the most extensive forest 

 re"-ion on the earth. The middle and upper portion of the course of the Amazon is 

 over 1,000 kilometers distant from the Atlantic Ocean, while it is separated, by 

 mountains from the Pacific. Were it not for the forests we ought to expect, at this 

 distance from the sea and. so near the equator, very high temperatures and great 

 dryness. The following table shows the results of the observations: 



Difference of temperatures of four stations in the hasin of the Amazon. 



Name of station. 



Para* 



Manaos 



Iquitos 



Peruarabiico* 



San Antonio on Madeira Kiver 



Height 



above 



sea. 



South 

 latitude. 



Meters. 



37 

 95 



Degrees. 

 3 



^ 



8 

 9 



Distance 



from 

 Atlantic. 



Eiloms. 



100 



1,150 



2,100 







1,750 



Temperature. 



Annual 

 mean. 



27.0 

 *26. 1 

 24.8 

 25.7 

 26.0 



Mean of 

 hottest 

 month. 



27.7 

 27.0 

 25.7 

 27.1 

 27.0 



Extreme 

 maxima. 



*35. 7 

 32.4 

 31.7 



Relative 



humidity 



for the 



year. 



*80 

 83 

 72 



* Ten months, from October to July. 



t Pernambiico doe.s not beloiijr to the Amazon basin; its means are only given for comparison with 

 those of San iutoiiio. The shore line near Periiambuco is wooded, but a certain distance around the 

 city the forests are cut down to give way to fields and sugar-cane plantations. 



Thus, owing to the vast primeval forests on the Upper Amazon and its tributaries, 

 the temiierature of the hottest month and the extreme maximum are not greater than 

 on the seacoast, and the extreme maximum is far from reaching the values some- 

 times observed in middle latitudes. It is also to be observed that there are few re- 

 gions on the earth where the "Trades" blow with such violence as on the coasts of 

 northern Brazil. Peruambuco is therefore subject not only to the influence of the 

 sea but also to that of a furious trade wind. Along the lower course of the Ama- 

 zon the " Trade" also blows with great force; but as soon as we turn into the side 

 valley of one of the tributaries running in a southerly and northerly direction calm 

 weather is found to prevail. The height and density of the forest arrests the wind. 

 There can be no doubt that the vast tracts of forest land on the Amazon, contribut- 

 iu'if to maintain the moisture of the air and weaken its motion, increase the amount 

 of waterfall. At Iquitos 284 centimeters fall in the course of the year. It must be 

 remembered that Iquitos lies in a plain 2, 100 kilometers from the ocean and 350 from 

 the mountains. Nowhere on the earth is the rainfall so great under similar circum- 

 stances. 



SUPPOSED INFLUENCE OF FORESTS UPON HAILSTORMS. 



In this coimection the chiimed iuflnence of forest areas upon hail- 

 storms may be discussed. While in France the conclusion was reached 

 that such influence existed, it is doubted by A. Biihler (Influence of 

 topography aud forests on frequency of hailstorms, 1890), who discusses 

 this question on the strength of observations over the whole Kingdom 

 of Wurtemberg through sixty years (1828-'87) in great detail. An in- 

 fluence either upon the frequency, intensity, or course of hailstorms, it 

 seems, could not be estabhshed. 



There is, however, in these statistics and the conclusions to be de- 

 rived therefrom one factor, that must not be overlooked, and which the 



12444— No. 7 9 



