146 PRACTICAL ARBORICULTURE 
Combinations of these various forces guide the currents of wind with 
varying direction and force according to predominating influences. At times 
a gentle zephyr, again the terrible tornado. Where uncontrolled as upon 
the ocean, a ship may lie becalmed for weeks, making no progress, and after- 
wards be carried to destruction by monster waves lashed into mountains by 
the typhoon. 
The same principle explains the snow drifts upon a farm or on the road- 
way in prairie countries. <A plain board fence and frequently a four wire 
fence simply causes the wind to form an eddy which deposits a drift of snow 
to such depth as to blockade the highway. It is often necessary to open the 
fields for the public to travel until the roads are cleared of snow. 
Builders of windmills understand that a high building or clump of trees, 
a hill or any obstruction near the wheel will prevent its successful operation 
when the direction of the wind is in line with such obstacle, although operat- 
ing perfectly while the direction is transverse to such lines. Here the eddy 
or whirling removes the pressure from the wheel and also causes the vane to 
vacillate. 
In the Ohio River, opposite the boyhood home of the author, is an im- 
mense sand bar, caused by a projecting ledge of rocks from the limestone hills 
of the Kentucky shore. In former years this bar extended entirely across the 
river, both above and below the town of Rising Sun, very shallow water cov- 
ering that portion called the channel, and steamboats were grounded on this 
bar with frequency. Engineers have constructed two dams projecting from 
the Indiana shore and one from the Kentucky side, in such manner as to con- 
fine the current so that the force of the stream deepens the channel, in order 
that boats may navigate more safely. 
Exactly the same principle governs the wind currents. A canyon in the 
mountains diverts the wind, directs its course, and at times increases its 
velocity. A range of high mountains or sharp hills deflect it upwards, while 
belts of trees perform the same service. 
Locomotive engineers inform me that in time of strong head or side 
winds these have a decided influence upon the train, retarding its progress, 
and when a belt of timber intervenes the strain upon the engine is relieved 
and the train shoots ahead with increased velocity. 
The whirlpool phenomenon in the Mississippi River, at Grand Gulf, Miss., 
which fifty years ago was noted as a most extraordinary instance of this 
reverse current and which gave the name to the then important locality, “Grand 
Gulf,” will be recognized by old river men, who knew the place in ante- 
bellum times. 
The river at that time occupied the great bend, which, since the “cut-off” 
and change in the river bed, has become an inland slough and island. The 
Big Black River empties into the Mississippi at this point, while a hard clay 
point projected from the Louisiana shore. The combination of forces during 
periods of high water caused this vast pool to whirl violently. Flat boats 
were often caught in this eddy, and it was with great difficulty thev were 
gotten out into the regular channel. The author, in his bovhood, has been in 
