The Hurricane Guide | Page 8

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The only difference between the above form and one for the reception
of corrected readings will be the dispensing with the column for the
attached thermometer, and placing under the word Barom.
"corrected."
II.--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.
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