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Phenomena Of Revolving Storms
Observations
Storms Hurricanes And Typhoons
Localities For Additional Observations
Lower Latitudes
Appendix
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

Seasons For Extra Observations

In reference to certain desiderata that have presented themselves in the
course of my researches on this subject (see Report of the British
Association for the Advancement of Science, 1846, p. 163), the _phases_
of the larger barometric undulations, and the _types_ of the various
seasons of the year, demand particular attention and call for extra
observations at certain seasons: of these, three only have yet been
ascertained--the type for the middle of November--the annual depression
on or about the 28th of November--and the annual elevation on or about
the 25th of December. The enunciation of the first is as under: "That
during fourteen days in November, more or less equally disposed about
the middle of the month, the oscillations of the barometer exhibit a
remarkably symmetrical character, that is to say, the fall succeeding
the transit of the maximum or the highest reading is to a great extent
similar to the preceding rise. This rise and fall is not continuous or
unbroken; in some cases it consists of _five_, in others of _three_
distinct elevations. The complete rise and fall has been termed the
great symmetrical barometric wave of November. At its setting in the
barometer is generally low, sometimes below twenty-nine inches. This
depression is generally succeeded by _two_ well-marked undulations,
varying from one to two days in duration. The central undulation, which
also forms the apex of the great wave, is of larger extent, occupying
from three to five days; when this has passed, two smaller undulations
corresponding to those at the commencement of the wave make their
appearance, and at the close of the last the wave terminates." With but
slight exceptions, the observations of eight successive years have
confirmed the general correctness of this type. On two occasions the
central apex has not been the highest, and these deviations, with some
of a minor character, form the exceptions alluded to. This type only has
reference to London and the south-eastern parts of England; proceeding
westward, north-westward, and northward, the symmetrical character of
this type is considerably departed from; each locality possessing its
own type of the barometric movements during November. The desiderata in
immediate connexion with the November movements, as observed in the
southern and south-eastern parts of England, that present themselves,
are--the determination of the types for November, especially its middle
portion, as exhibited on the oceanic surface within an area comprised
between the 30th and 60th parallels, and the 1st and 40th meridians
west. Vessels sailing within this area may contribute greatly to the
determination of these types by making observations at intervals of
three hours from the 1st of November to the 7th or 8th of December. The
entire period of the great symmetrical wave of November will most
probably be embraced by such a series of observations, as well as the
annual depression of the 28th. For the elevation of the 25th of December
the three-hourly observations should be commenced on the 21st, and
continued until the 3rd or 4th of the succeeding January.

With respect to the great wave of November, our knowledge of it would be
much increased by such a series of observations as mentioned above,
being made on board surveying and other vessels employed off Scotland
and Ireland; vessels navigating the North Sea; vessels stationed off the
coasts of France, Spain, Portugal, and the northern parts of Africa, and
at all our stations in the Mediterranean. In this way the area of
examination would be greatly enlarged, and the _differences_ of the
curves more fully elucidated; and this extended area of observation is
the more desirable, as there is some reason to believe that the line of
greatest symmetry _revolves_ around a fixed point, most probably the
nodal point of the great European systems.

It is highly probable that movements of a somewhat similar character,
although presenting very different curves, exist in the southern
hemisphere. The November wave is more or less associated with storms. It
has been generally preceded by a high barometer and succeeded by a low
one, and this low state of the barometer has been accompanied by stormy
weather. We are therefore prepared to seek for similar phænomena in the
southern hemisphere, in those localities which present similar states of
weather, and at seasons when such weather predominates. We have already
marked out the two capes in the Southern hemisphere for three-hourly
observations: they must doubtless possess very peculiar barometric
characters, stretching as they do into the vast area of the Southern
Ocean. It is highly probable that the oscillations, especially at some
seasons, are very considerable, and vessels visiting them at such
seasons would do well to record with especial care the indications of
the instruments already alluded to. At present we know but little of the
barometric movements in the Southern hemisphere, and every addition to
our knowledge in this respect will open the way to more important
conclusions.

It has been observed in the south-east of England that the barometer has
generally passed a maximum on or about the 3rd of every month, and this
has been so frequently the case as to form the rule rather than the
exception. The same fact during a more limited period has been observed
at Toronto. With especial reference to this subject the three-hourly
series of observations may be resorted to in all localities, but
especially north of the 40th parallel in the northern hemisphere. They
should be commenced at midnight immediately preceding the 1st and
continued to midnight succeeding the 5th.

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