RAINFALL IN MINNESOTA. 449 
RAINFALL IN MINNESOTA. 
EDWARD A. BEALS. 
U.S. Signal Service Station, Minneapolis. 
If we could obtain during the growing season the proper distri- 
bution of the meterological elements of temperature, sunshine and 
rainfall, agricultural pursuits would become an exact science, and 
it would soon be possible for us to determine at the time of planting, 
almost to the bushel, what yield would accrue from each cultivated 
acre. 
Ail of these elements can to some extent be controlled artificially: 
that of temperature being accomplished in greenhouses through 
methods familiar to all; that of sunshine by the electric light, pro- 
vided its rays are filtered through glass; and that of rainfall by 
means of irrigation, which is a comparatively cheap, practical and 
efficient substitute for its deficiency, whether habitual or otherwise. 
The control of temperature and sunshine presents difficulties that 
render impracticable their application to extended areas; but in 
Minnesota this is of no particular consequence, as nature seldom 
fails to provide the right proportion of each for maturing those 
plants which are of the greatest importance to mankind. In the 
case of the remaining element, that of rainfall, we are not so fortu- 
nate; although the amount annually received is rarely insufficient, 
still severe drouths, doing great damage, are altogether too com- 
mon, being largely caused by variability in its distribution. 
We should not feel, however, that these occasional dry spells were 
due in any way to arighteous discrimination, as there is no region | 
in the United States absolutely free from them, even including 
those places where the annual rainfall is in excess of one hundred 
inches. 
The introduction by man of water upon land has, besides a minor 
use as a protection against frost, three distinct objects in view, one 
of which is the making of tillable land out of barren land through 
the sedimentary deposits thus obtained; a second purpose is the 
acquisition by precipitation of fertilizing materials held in solution; 
while the third and more general use is the making up of either per- 
manent or temporary deficiencies in rainfall. It is probable that 
for many years to come the only necessity for irrigation in Minne- 
sota will be for emergency uses during dry spells, and therefore it 
should properly be first introduced on a small scale in connection 
with horticulture and gardens. 
Not the least of the conditions to be considered before its success- 
ful application can be accomplished is the drainage area available, 
the proportion of storable to percolating and evaporating water and 
the rainfall. 
Local evaporation is occasionally the source of rainfall, but in 
Minnesota the vapor-laden winds from the Gulf of Mexico, the At- 
lantic Ocean and the Great Lakes, perhaps also including those 
from Hudson Bay and the Arctic Ocean, largely preponderate in 
supplying us with the moisture received. These reservoirs are 
inexhaustible, and no fears need be entertained regarding their per- 
