The Sun.
London, England, 1860-11-22 00:00:00

TILE WEATHER.

The following remarks by Rear-Admiral Fitzroy
appear in the Atheneum of Saturday :
" Board of Trade, Nov. 12.
" An alteration in the words or scales of barometers
having been suggested, and daily tables of weather having
been lately published, respecting which various questions
have arisen, may I, as the person responsible for them,
venture now to submit a few brief remarks on the subjects
of these alterations and ' Weather Tables ?'
" 1. As it is impossible to have many words on a baro-
meter scale that may be read easily without a lense, my aim
has been to condense the purport of a few words, most
wanted, in a systematic manner, as notes adverting to in •
structions elsewhere, and of general application.
" 2. By comparison with the meteorological reports now
published daily one may ascertain the state of a barometer,
iinerord;--cir aympiesometer, or elevation above the sea level,
by comparisons made between eight and nine in the morn-
ing, with two or three of the observations published, for
the same time, and for places near, but on different sides.
" 3. It is unnecessary to draw general attention to the
use of such a continuous, uniform, and simultaneous series
of observations as are available in these tables; but to prac-
tical seafaring members of our very maritime community
—to pilots and fishermen, especially, who may possess
weather-glasses and may take this easy method of verifying
them while studying the weather with these daily reports,
they should be found invaluable.
" 4. Aneroids are now made more portable, so that a
pilot or chief boatman may carry one in his pocket, as a
railway guard carries his timekeeper; and, thus provided,
pilots cruising for expected ships would be able to caution
strangers arriving, if bad weather were impending, or give
warning to coasters or fishing boats.
"5. Harbours of refuge, however excellent and import-
ant, are not always accessible even when most wanted, as
in snow, rain, or darkness, when neither land, nor buoy,
nor even a lighthouse light can be seen.
" 6. Not only do these daily statements of weather and
indications of accurate instruments show, to all who are
sufficiently interested to compare them day by day (aided
perhaps by a map with wind-markers), the present and re-
cently past character of the weather generally, and in many
specified places—but they enable one to foresee the probable
nature of wind and weather, during the next day or two,
even the next few following days.
" 6. Recent comparisons of accumulated facts have in-
duced the conclusion that winds move in parallel currents,
or circulate around a centrical area; and that whether the
extension of such movement or circulation be immense, as
between the tropics and the polar regions, or whether it be
small even as the dust-whirl, the laws of circulation, or
gyration,* are uniform, except in very rare and limited cases.
" 8. When movememts of the atmosphere, such as those
of the perennial trade-winds, or the very prevalent westerly
winds, or anti-trade winds,'t are on the largest scale, the
wind appears, at any one place, to move in straight lines,
owing to the really circular arc having so little curvature ;
but when circulation is comparatively limited, as in a cy-
clone, rapid changes in the wind's direction, are obvious to
every observer.

"9. When such movements are not horizontal, but in-
clined to the surface, more or less, perhaps nearly vertical,
or partaking of varied directions, they are exceedingly diffi-
cult to trace, except by upper clouds seen crossing heavenly
bodies, or by visits to high mountains, or by examining
dustl. (so called) carried from far distant places through
the higher regions of our atmosphere.
" 10. Nevertheless, it appears from the facts ascertained,
that the current (from polar regions) tends upward when
intermediate between the tropics, and then as a tropical cur-
rent, eastward, while the lower or polar movement is south-
ward, and, apparently, westward. Apparently, because it
is caused by the earth turning towards the east ; not by its
own inclination or impulse, which is solely southerly. Near
the equator it has almost acquired that equatorial, rather
than centrifugal impetus, which, as it 'ism into an upper
region, causes it to move eastward while returning towards
the pole, but losing this impulse as it approaches that
centre.

" 11. This circulation, therefore, closely followed out, is
similar to that of all the smaller cyclonic motions(ellipsones?)
against watch-hands in north latitude, with the hands of a
watch in the southern hemisphere.
" 12. A practical, important, and hitherto unnoticed con-
sequence of these facts is, that lines drawn on a map at
right angles to the right (left in south latitude) of the
wind's direction towards any one facing it, all tend more or
less toward the centrical area (whether oval, elliptic, or
circular), around which there is then a movement of circu-
lation, more or less varying ; and, therefore, that a fair
average of such lines of direction (radii), drawn from vari-
ous stations, will show (where they intersect each other most
nearly) the approximate centre of such general circulation,
which, even thus roughly ascertained, may enable any per-
son acquainted with cyclonology to complete the circles on
paper, show how the wind is then blowing, its probable re-
lative strength at any parts around them, and over what
countries or coasts the central part of such circulation will
probably pass.

" 13. Having this knowledge, it immediately follows that
telegraphic warning may be sent in any direction reached
by the wires, and that, occasionally, on the occurrence of
very ominous signs, barometric and other—including al••
ways those of the heavens—such cautions may be given be-
fore storms as will tend to diminish the risks, and loss of
life, so frequent on our exposed and tempestuous shores.
" 14. It has been proved that storms, indeed all the
greater circulations of atmosphere, between the tropics and
the polar regions, have an eastward motion, bodily, while
circulating around a centrical area.
" 15. This universal motion (however irregular or modi-
fied, in some few localities, by exceptional and minor causes
is independent of the regular circulation above-mentioned,
which, when compressed by the earth's surface, or other-
wise, has the effect of movements like the ' parallel cur-
rents,' as first spoken of by Dove. These circulations of
the polar and tropical currents, with their attendant pecu-
liarities of dry, cold, and heavy air, or moist, warm, and
light air, raising or lowering the barometer, as they pass
over any country, have probably caused the idea of ' atmo-
spheric waves' corresponding to barometrical oscillations,
as well as to the gyrations' of wind, so well elucidated by
that meteorologist.

" 16. Such prolonged and excessively broad currents are
always flowing, in nearly opposite directions, if side by side
near the earth's surface, or parallel; but if overlapping, or
entirely superposed, crossing in various directions, and
more or less impinging on or intermingling with each other.
These greater currents, incessantly in motion, occasion by
their eddies the minor movements of cyclones, successive
and perhaps numerous—one cyclone following, impinging
on, or counteracting another, more or less, and thus caus-
ing those complicated changes of wind, sudden shifts, and
apparent contradictions of the general law, which have so
bafed some investigations, and have caused doubts as to
the reliability and universality of the laws of storms.

" 17. While these normal polar and tropical currents are
respectively moving towards wide intertropical regions, and
toward those very limited spaces around the poles of our
world, they have, as has been stated, a general movement
in mass, laterally, towards the east.

" 18. The body of air raised (rarefied by warmth, loaded
with vapour, and expanded) around the whole globe, about
its equatorial bulk, is vastly greater than the aggregate of
cold, dry, condensed and heavy air in the polar regions.
This equatorial mass of air around the world has acquired
a temporary impulse eastward with nearly the velocity of
rotation in that zone, but prevented by gravitation from
rising above a certain distance, pressed on by air in motion
below (or behind), toward either pole it must go, to equi-
librate the atmosphere.
" 19. "While moving toward the pole, retaining for a
time, though gradually losing, its acquired eastward mo-
tion, which is continued only till the momentum due to its
weight and velocity fails in effect towards the polar circles
—there must be a continued impact, a constant impulsion
from the westward against the polar current laterally, as
it is drawn towards, and after the sub-solar rising part of
the atmosphere.
" 20. The polar current has no lateral impulse of its own
—it is drawn towards the west, in appearance only, because
the earth's surface has a greater rotatory velocity eastward
than the polar current, proportionally to its approach to the
equator • while, on the other hand, that current is gra-
dually acquiring equatorial motion.
"21. Therefore the sensible effect on the whole system
of circulation must be continual easterly progression, a
general motion of the atmosphere towards the east, even in
the lower (perennial) trade-winds, where its motion is only
less different from that of the earth's surface than it is in
higher latitudes.
" 22. The continuous impulse of the tropical current east-
* Dove. t Herschel. Asko, or inineoria,

trici ty.
" 25. During such a normal condition of atmosphere the
return, or tropical current, passed above, is only made
evident to us by light upper clouds seen crossing heavenly
bodies, and by the evidence of feeling, at high elevations,
on mountains or in balloons.
" 26. At other times, and by far the more prevalent,

there is a more or less conflicting alternation, along the
earth's surface, or in the upper air, of the great principal
currents, in such a variety of proportion and combination,
that observers, however careful and discriminating, cannot
be otherwise than perplexed until more is ascertained, not
only of the mechanical, but the chemical and electrical laws
of the atmosphere. With the tropical current there is little,
if any, positive electricity manifested in the air. Some-
times, and particularly with moist deposit, there is negative
electricity in a greater or less degree.
" 27. Part of the tropical current descends, between the
latitudes of 20 and 35 degrees, turas towards the equator,
and combines with the perennial or the periodical winds.
Part flows on towards the polar region, invariably coming
down, or descending towards the earth's surface, wherever
the polar current fails; and then, having obtained access,
it increases in breadth and strength till a revival of the
polar element enables it to turn, overcome, and eventually
displace its usurping antagonist.

I "28. As the polar current diminishes or fails gradually
while moving southward, and as the first descent of the
tropical stream is more or less from the westward, the
feeble extremities of the polar current are turned to the
eastward, and, as they become combined with the advanc-
ing tropical stream, turn actually northward till lost—thus
causing a rotary movement against watch-hands—a move-
ment as constant in the north hemisphere as its analogous
motion, in the contrary direction, is general in southern
latitudes.

"29. When the polar current recovers energy, being re-
cruited from far remote sources, it usually presses suddenly
and violently against the polar side of the tropical current,
which is flowing from the southward and westward, mak-
ing it diverge in direction by curving away from the place
of most pressure, and thus increasing the tendency to
circulate, as above mentioned, in one direction rather than
another. These currents combine, or mix, variously, in
nature as well as in direction. There may be also an elec-
trical agency, not yet ascertained and traced distinctly,
though frequently indicated.

"30. In conclusion, let me remark that, although these
appear to be general outlines in accordance with observed
facts, it ought to bo borne in mind that similar features or
peculiarities occur on a very small scale in some localities,
and apparent exceptions or contradictions in others (such
as temporary land or sea breezes, occasional gyrations of a
local whirlwind or waterspout, contrary to usual law) ; so
exceptional, however, that they may truly be said to prove
the generality of those laws so necessary to be studied by
seamen."