given satisfactory results.

Lind's anemometer, which consists simply of a U tube containing liquid
with one end bent into a horizontal direction to face the wind, is
perhaps the original form from which the tube class of instrument
has sprung. If the wind blows into the mouth of a tube it causes an
increase of pressure inside and also of course an equal increase in
all closed vessels with which the mouth is in airtight communication.
If it blows horizontally over the open end of a vertical tube it
causes a decrease of pressure, but this fact is not of any practical
use in anemometry, because the magnitude of the decrease depends on
the wind striking the tube exactly at right angles to its axis,
the most trifling departure from the true direction causing great
variations in the magnitude. The pressure tube anemometer (fig. 1)
utilizes the increased pressure in the open mouth of a straight tube
facing the wind, and the decrease of pressure caused inside when the
wind blows over a ring of small holes drilled through the metal of
a vertical tube which is closed at the upper end. The pressure
differences on which the action depends are very small, and special
means are required to register them, but in the ordinary form of
recording anemometer (fig. 2), any wind capable of turning the vane
which keeps the mouth of the tube facing the wind is capable of
registration.

[v.02 p.0003]

The great advantage of the tube anemometer lies in the fact that the
exposed part can be mounted on a high pole, and requires no oiling
or attention for years; and the registering part can be placed in any
convenient position, no matter how far from the external part. Two