56 National Geographic Magazine. 
flows at various places on the Mississippi and Missouri and Ohio - 
rivers, were tabulated from data given in the reports of the 
Mississippi and Missouri River Commissions. The tables were 
largely derived from the results of the measurement of current 
velocities. As gauge readings were taken at the time of dis- 
charge or outflow measuremerts, the discharges or outflows can 
be told approximately at other times when only the river gauge 
‘readings are known, The results for the outflow of rivers 
derived from measurements made under the supervision of these 
commissions, are of a high order of accuracy, and it is not prob- 
able that the results deduced from the gauge readings are much 
in error. Of 1881 and 1882, during which years measurements 
were made, 1881 was a year of great flood in the Missouri river, 
while the Mississippi river was not flooded. The year 1882, on 
the other hand, was marked by a great flood in the lower Missis- 
Sippi river, with a stage in the Missouri much above the average. 
The rainfall in the six great valleys of the Mississippi, during the 
entire years 1881 and 1882, was charted from all observations 
available, and its amount in cubic miles of water calculated with 
the aid of a planimeter. 
In connection with this investigation, and as a matter of value 
in showing the forces which are in operation to affect the river 
outflow, the fictitious or possible evaporation of the six great 
valleys referred to were calculated, in cubic miles of water, from 
July, 1887, to July, 1888, and also the average amounts of water 
in the air as vapor, and the amount required to saturate the air 
in the same valleys during the same period. 
During the year 1882, the year of great flood in the lower 
Mississippi valley, the outflow at Red River Landing, La., was 
202.7 cubic miles, of which the upper Mississippi river above St. 
Louis furnished 16 per cent., the Ohio 43, and the whole Missouri 
above Omaha, 4 per cent. The upper Missouri valley (that is, 
from the mouth of the Yellowstone up to the sources), and the 
middle Missouri valley (from the mouth of the Platte to the 
Yellowstone), each furnished only about 2 per cent. of the entire 
amount of the water which passed Red River Landing. The 
lower Mississippi valley, including the Arkansas, etc., furnished 
32 per cent. 
During March, April and May, 1882, the time of highest stage 
of the water of the lower Mississippi, the outflow at Red River 
Landing and through the Atchafalya measured 82.7 cubic miles, 
pa we 
