respect captains and
masters of vessels may render essential service by observing and
recording the state of the barometer, and direction and force of the
wind, several times in the course of the day and night;[3] and when it
is considered that the immediate object in view is one in which the
mariner is personally interested, and one in which, it may be, his own
safety is concerned, it is hoped that the keeping of a meteorological
register having especial reference to the indications of the barometer,
and force and direction of the wind, will not be felt as irksome, but
rather will be found an interesting occupation, the instruments standing
in the place of faithful monitors, directing when and where to avoid
danger, and the record furnishing important data whereby the knowledge
of general laws may be arrived at, having an essential bearing on the
interests of the service at large.

CHAPTER III.

OBSERVATIONS.

In sketching out a system of observation having especial reference to
atmospheric waves and rotatory storms, regard has been had--_first_, to
the instruments that should be used, the observations to be made with
them, the corrections to be applied to such observations, and the form
of registry most suitable for recording the results: _second_, to the
times of observation: _third_, to the more important localities that
should be submitted to additional observation: _fourth_, to peculiar
phaenomena requiring extraordinary observations for their elucidation:
and _fifth_, to particular seasons, when the instruments should be
watched with more than ordinary care.

The more important objects of observation having especial reference to
atmospheric waves are those points which have been termed _crests_ and
_troughs_. These are simply the _highest_ and _lowest_ readings of the
barometer, usually designated _maxima_ and _minima_, and should for the
object in view receive particular attention. Whenever there is reason to
believe that the barometer is approaching either a _maximum_ or
_minimum_, additional observations should be resorted to, so as to
secure as nearly as possible _the precise time_ as reckoned at the ship,
with her position, of its occurrence, as well as the altitude of the
mercurial column at that time and place. By means of such observations
as these on board several ships scattered over the surfaces of our great
oceans, much valuable information may be accumulated of a character
capable of thr