12 
A 25-mile wind is not uncommon on the Plains, and since it causes 
six times the evaporation that would occur in a calm at the same 
humidity and temperature, one can easily understand the rapidity 
with which the moisture from a summer shower disappears. Taken 
the year through, the wind averages more than 10 miles an hour, 
which is sufficient to cause four times the evaporation there would be 
in a calm. 
An experiment made by King? furnishes some interesting infor- 
mation in regard to the checking of evaporation by a windbreak. He 
used a modified form of the Piche instrument, placed so as to give the 
evaporation from a water surface 1 foot above the ground at varying 
distances from an cak grove. Taking the evaporation at 20 feet from 
the grove as unity, the following results were obtained: 
[Pesca | Evapo- ||,.. | Evapo- 
Distance. ration, || Distance-| 7 tion. | 
~ 20 | 1.00 | 200 LAL | 
100 1.29 300 1.66 | 
Neither the height of the grove nor the rate of wind is given, 
though the statement is made that a light wind was blowing. The 
table shows that the evaporation at 200 feet from the windbreak was 
41 per cent more than at its base, and at 300 feet 66 per cent more. 
The. evaporation from 300 feet onward was practically constant, 
showing that to be the limit of the influence of the windbreak in 
this experiment. 
While a few accurate experiments have been made to determine 
how far a windbreak is effective, it is a safe practical assumption 
that it protects the ground for a distance equal to ten or fifteen times 
its height—some observers say a rod for every foot. Ifa large field 
were crossed by a series of windbreaks 30 feet high and 20 rods apart, 
there is no doubt that they would be very effective, since the wind 
would reach each succeeding break with diminished force. 
WOODLOTS. 
In many situations it will be a paying investment for the farmer 
to put out a small plantation, simply to produce his own wood for 
fuel and other purposes. It is true that some time must elapse be- 
fore the plantation begins to be productive, but by choosing rapid- 
growing species and planting closely the thinnings which will ‘be 
necessary in a few years, even though the trees be small, will do for 
the wood pile and help make the owner independent of coal famines. 
7. H. King, Bulletin No. 42, Agric. Exp. Sta., University of Wisconsin, 
October, 1894. 
[Cir. 161.] 
