Yol. 65.] ANNIVERSARY ADDRESS OE THE PRESIDENT. XCi 



The method used by Prof. Joly in arriving at an estimate was 

 based on the results of an investigation published by Sir John 

 Murray. 1 



Two factors enter iuto the calculation, whatever method is 

 employed : these are first the volume of the water discharged by the 

 rivers, and next the chemical composition of this water as deter- 

 mined by analysis. 



To find the volume of the water Sir John Murray estimated 

 (1) the total rainfall of the globe and (2) the fraction of this which 

 flows away in rivers. The fraction is taken as - 222," and this 

 multiplied into the rainfall gives 6,524 cubic miles, a result which 

 must of course be regarded as only roughly approximate. 3 



1 Scottish Geogr. Mag. he. cit. 



2 This fraction is of fundamental importance to our enquiry. Sir John 

 Murray does not give the data on which it is based. In the few instances 

 known to me its value is generally much higher, as will be seen from the 

 following table : — 



Rhine (Cologne) 0-518 I Muskigum 0-330 



Weser (Baden) 0-347 Genesee 0352 



Elbe (Geisthacht) 0263 Croton 0'461 



Oder (Kiistrin) 0"255 I Hudson 0527 



Vistula (Stromtutz) 0'255 Connecticut - 511 



Memel (Stromtutz) 0339 J James 0327 



Danube (Vienna) 0526 Mississippi 0'25 



Rhone (mouth) 0-878? Rio Grande (El Paso) 0237? 



Garonne 0'532 Androscoggin 0'555 



Klarelf (Sweden) 0750 , Colorado 0-190? 



Fyris 0350 j 



3 The latest account of the distribution of rainfall is given by Supan 

 (A. Supan, 'Die Verteilung des Niederschlags auf der festen Erdoberniiche ' 

 Petermann's Mitth. 1898, Erganzungsheft No. 124). His results are plotted 

 on a map, and I have transferred them to another map constructed upon the 

 principle of equal areas, so that, by cutting out the regions of equal rainfall, I 

 could approximately estimate the amount of rainfall by weighing them. In 

 this way I obtained the following : — 



Area of Land Total rainfall in 



in square miles. Rainfall in inches. cubic miles. 



12,281,923 to 10, mean 5 969 



12,823,335 10 to 20, „ 15 3,036 



6,668,886 20 to 30, „ 25 5,457 



6,336,712 30 to 40, „ 35 3,501 



10,965,458 40 to 80, ,, 60 10,390 



3,191,886 804- „ 80+- 3,023+ 



52,2(>8,200 26,3764- 



The Antarctic continent and the greater part of Greenland have been excluded' 



92 



