As the flags, however, belong
more especially to Sergeant G---- 's duty on the field of battle or to
exceptional cases of storm and danger, we pass them by to examine into
his daily round of duty. Outside, a queer little house of lattice-work
perched on a headland shelters the thermometers and barometers: on
a still higher point directly over the foaming breakers is the
anemometer, the little instrument which measures the swiftness of the
fiercest cyclone as easily as the lightest spring breeze. It consists
of four brass cups shaped to catch the wind, and attached to the ends
of two horizontal iron rods, which cross each other and are supported
in the middle by a long pole on which they turn freely. The cups
revolve with just one-third of the wind's velocity, and make five
hundred revolutions whilst a mile of wind passes over them. A register
of these revolutions is made by machinery similar to a gas-meter.
The popular idea, by the way, of the speed of the wind runs very far
beyond the truth: we are apt to say of a racer that he goes like the
wind, when the fact is the horse of a good strain of blood leaves the
laggard tempest far behind; the ordinary winds of every day travel
only five miles an hour, a breeze of sixteen and a quarter miles an
hour being strong enough to cause great discomfort in town or field:
thirty-three miles is dangerous at sea, and sixty-five miles a violent
hurricane, sweeping all before it.
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