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Phenomena Of Revolving Storms
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Phenomena Of Atmospheric Waves
Seasons For Extra Observations
Avoiding The Centres Of Rotating Storms
Times Of Observation

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Times Of Observation
Avoiding The Centres Of Rotating Storms
Seasons For Extra Observations
Phenomena Of Atmospheric Waves
Appendix
Lower Latitudes
Localities For Additional Observations
Storms Hurricanes And Typhoons
Observations
Phenomena Of Revolving Storms

Times Of Observation

There can be no question that the greatest amount of information, the
accuracy of the data supplied, and in fact every meteorological element
necessary to increase our knowledge of atmospheric waves, may be best
obtained by an uninterrupted series of _hourly_ observations made on
board vessels from their leaving England until their safe arrival again
at the close of their respective voyages; but from a variety of
circumstances--the nature of the service in which the vessels may be
employed, particular states of the weather, &c.--such a course of
unremitting labour cannot be expected; it is therefore necessary to fix
on some stated hours at which the instruments before particularized
should be regularly observed throughout the voyage, and their
indications faithfully recorded. The hours of 3 A.M., 9 A.M., 3 P.M.,
and 9 P.M., are now so generally known as _meteorological hours_, that
nothing should justify a departure from them; and it is the more
essential that these hours should be adopted in the present inquiry,
because the series of observations made at intervals terminated by these
hours can the more readily be used in connexion with those made
contemporaneously on land, and will also serve to carry on
investigations previously instituted, and which have received
considerable illustration by means of observations at the regular
meteorological hours; we therefore recommend their general adoption in
all observations conducted at sea.

It is intended in the sequel to call attention to particular parts of
the earth's surface where it is desirable that additional observations
should be made, in order to furnish data of a more accurate character,
and to mark more distinctly barometric changes than the four daily
readings are capable of effecting. The best means of accomplishing this
for the object in view appears to be the division of the interval of six
hours into two equal portions, and to make the necessary observations
eight times in the course of twenty-four hours. In the particular
localities to which allusion has been made we recommend the following as
the hours of observation:--

A.M. 3, 6, 9, noon. P.M. 3, 6, 9, midnight.

In other localities besides those hereafter to be mentioned, when
opportunities serve, readings at these hours would greatly enhance the
value of the four daily readings.

There are, however, portions of the surface of our planet, and probably
also phænomena that occur in its atmosphere, which require still closer
attention than the eight daily readings. One such portion would appear
to exist off the western coast of Africa, and we recommend the adoption
of _hourly_ readings while sailing to the westward of this junction of
aqueous and terrestrial surface; more attention will be directed to this
point as we proceed. There are also phænomena the localities of which
may be undetermined, and the times of their occurrence unknown, but so
important a relation do they bear to the subject of our inquiries, that
they demand the closest attention. They will be more particularly
described under the head of accumulations of pressure preceding and
succeeding storms, and minute directions given for the hourly
observations of the necessary instruments. In the mean time we may here
remark that hourly observations under the circumstances above alluded to
are the more important when we consider that the barometer, the
instrument employed in observing these moving atmospheric masses, is
itself in motion. The ship may meet the accumulation of pressure and
sail through it transversely; or she may sail along it, the course of
the vessel being parallel to the line marking the highest pressure, the
ridge or crest of the wave; or the ship may make any angle with this
line: but whatever the circumstances may be under which she passes
through or along with such an accumulation of pressure, it should ever
be borne in mind that her position on the earth's surface is scarcely
ever the same at any one observation as it was at the preceding, the
barometer in the interval has changed _its_ position as well as the line
of maximum pressure, the rate of progress of which it is desirable to
observe. It will, therefore, be at once apparent that in order to obtain
the most accurate data on this head hourly observations are
indispensable. To these readings should of course be appended the places
of the ship from hour to hour, especially if she alter her course much.

There is another point to which we wish to call attention in immediate
connexion with hourly readings--it is the observation of the instruments
on the days fixed for that purpose: they were originally suggested by
Sir John Herschel, whose directions should be strictly attended to: they
are as follows:--

The days fixed upon for these observations are the 21st of March, the
21st of June, the 21st of September, and the 21st of December, being
those, or immediately adjoining to those of the equinoxes and
solstices, in which the _solar influence_ is either stationary or in a
state of most rapid variation. _But should any one of those 21st days
fall on a Sunday, then it will be understood that the observations are
to be deferred till the next day, the 22nd._ The series of observations
on board each vessel should commence at 6 o'clock A.M. of the appointed
days, and terminate at 6 A.M. of the days following, according to the
usual reckoning of time adopted in the daily observations.

In addition to the twenty-five hourly readings at the solstices and
equinoxes as above recommended, it would be desirable to continue the
observations until a complete elevation and depression of the barometer
had been observed at these seasons. This plan is adopted at the Royal
Observatory, Greenwich, and would be attended with this advantage were
it generally so--the progress of the elevation and depression would be
more readily traced and their velocities more accurately determined than
from the four or eight daily readings.

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