Geography of the Avr. 55 
may again fall as rain on other land. But the pertinence of 
meteorological investigations in connection with irrigation and 
this annual address, relates much more directly to important 
questions of the manner by, and extent to which, precipitation 
over the catchment basins of the great central valleys fails to 
return in direct and visible form, through the water courses, to 
the Gulf of Mexico. 
The inter-relation of rainfall and river outflows is one of pecu- 
liar interest, in connection with the important matter of irriga- 
tion now under consideration in this country. 
Probably more attention has been paid to this subject in the 
valley of the Seine, by Belgrand and Chateaublanc, than in any 
other portion of the globe. One of the curious outcomes of Chat- 
eaublanc’s observations, is one bearing on the maximum value of 
the floods in the Seine for the cold season, from October to May, 
by which he says that the reading of the river gauge at Port 
Royal is equal to 12.7 minus the number of decimetres of rain- 
fall which has fallen on an average throughout the catchment 
basin during the preceding year. This curiously shows that the 
intensity of the winter floods of the Seine is inversely propor- 
tional to the quantity of rain of the preceding year. 
Sometime since, John Murray, Esq., in the Scottish Geographic 
Magazine, treated generally the question of rainfall and river 
outflows. The annual rainfall of the globe was estimated to be 
29,350 cubic miles, of which 2,343, falling on inland drainage 
areas, such as the Sahara desert, etc., evaporate. The total 
annual discharge of rivers was estimated at 7,270 cubic miles. 
In the case of European drainage areas between a third and a 
fourth of the rainfall reaches the sea through the rivers. The 
Nile delivers only one thirty-seventh of the rainfall of its catch- 
ment basin, while tropical rivers in general deliver one-fifth. 
The Saale river of Germany, from late data based on 45 rain- 
fall stations in its catchment basin, during the years 1883 to 
1886, discharged 30 per cent. of its rainfall. 
During the past year Professor Russell, of the Signal Office, 
has determined carefully the rainfall and river outflow over the 
most important part of the United States, the entire catchment 
basin of the Mississippi river and its tributaries. This work was 
done as preliminary to formulating rules for forecasting the 
stage of the water several days in advance on the more import- 
ant of the western rivers in the United States. The river out- 
