In presenting to the National Geographic Society a summary of
geographic advance as regards the domain of the air, the Vice-president
finds a task somewhat difficult. The traveler passes from the east to
the west coast of Africa, and his very efforts to struggle across that
great continent, impress in his memory an abiding picture of the
physical features of the country over which he has passed, and of the
distribution of plants and animal life. So, too, a vessel sails from
one coast to another, casting here and there a sounding lead, from
which measurements it is possible to give quite a definite idea of the
relief features of the bottom of the sea.
Small as are the traces which serve to indicate the character of the
sea bottom, yet they are infinitely greater than those which enable us
to give a description of the air. Atmospheric disturbances are so vast,
and their action is so rapid, that it requires the attentive care of
thousands of observers before one can well hope to draw the roughest
figure of a passing storm. To note changes in the force and direction
of the wind, to note the depth of the rain, the increase and decrease
of temperature and the varying changes of aqueous vapor, either in
visible or invisible form, requires millions of careful, systematic
observations, and then when these are made, the task of collating,
elaborating and discussing them seems almost too great for any man.
Fortunately the value of meteorological work has impressed itself not
only upon governments, which have assisted liberally by appropriations
and organization, but yet more upon the isolated observer, thousands of
whom over the face of the earth give of their time and labor, and add
their mite to the wealth of universal knowledge.
In connection with all great physical questions, there is at times a
tendency to application to special phases somewhat to the exclusion of
others. While it can hardly be said that scientific and theoretical
discussion of meteorology has been unduly neglected during the past
year, yet it is evident that the greatest activity of meteorologists
has been devoted to climatological investigation, and compilations of
this character have been particularly numerous during the past
year--not in the United States and Europe alone, but throughout the
whole world.
The growing practical importance of meteorological researches has been
lately evidenced perhaps in no more striking way than in the
establishment in Brazil of a most extensive meteorological service,
created by a decree of the Imperial government on April 4, 1888. A
central meteorological institute, under the Minister of Marine, is to
be the centre for meteorological, magnetic and other physical
researches, and observations are to be made at all marine and military
establishments in the various provinces, on the upper Amazon, in
Uruguay, and on all subsidized government steamers. This service should
soon be fruitful in results, as the meteorology of the interior of
Brazil is almost absolutely unknown.
Another vast scheme has originated in Brazil in the Imperial
Observatory of Rio Janeiro. Señor Cruls, its director, contemplates a
dictionary of the climatology of the earth, giving monthly means and
extremes of pressure, temperature, rainfall, wind, etc. This scheme, of
course, can be successful only by international co-operation. The
United States Signal Service has pledged its aid as regards this
country.
The former tendency among Russian meteorologists to devote their
greatest energies to climatological compilations has gradually given
way to other practical work in connection with weather and storm
predictions, as shown by the institution by the Russian government of a
system of storm-warnings for the benefit of vessels navigating the
Black Sea.
Blanford has put forth an important paper, which partially elucidates
the very intricate question of diurnal barometric changes, particularly
bearing on the relation of the maximum pressure to critical conditions
of temperature, cloudiness and rainfall. The question viewed in a
negative light by Lamont, as to whether the maximum barometric pressure
could be attributed to the greatest rate of increase in the temperature
of the air, due, it is supposed, to the reactionary effect of the
heated and expanding air, has been re-examined by Blanford, whose
conclusions are somewhat in favor of this theory.
S. A. Hill has treated of the annual oscillation of pressure, so
noticeable in India, and in so doing has investigated the changes of
pressure for three levels, up to a height of 4500 meters. The reduction
of monthly barometric means at high levels, having regard to the
vertical distribution of temperature, shows a double oscillation in the
annual curve at the level of Leh, which becomes a single one at the
height of 4500 meters, while this is substantially the reverse of the
oscillation observed below.
The subject is also treated in another way by Mr. Hill, through
analysis of normal monthly means for all India, whereby he succeeds in
presenting a formula, the first periodic terms of which represent the
two principal factors of the oscillation.
Mr. Hill has also discussed elaborately the anomalies in the winds of
northern India in their relation to the distribution of barometric
pressure. The anomalies are:--(1) in the hot season the wind direction
frequently shows no relation to the barometric gradient; (2) the winds
over the plains show little or no relation to pressure gradients, but
an obvious one to temperature, being greatest where the temperature is
highest.
It is pointed out as highly probable that the copious snowfalls of the
late winter in the northwest Himalayas not only produce low
temperatures on the Himalayan ranges, but subsequently cause dry
northwesterly winds over northern and western India, and on this
supposition, reliable forecasts of the character of the coming rainy
monsoons have been made for a number of years. Convection currents
between upper and lower air strata, it is suggested by Koppen, explain
diurnal variations in wind velocity and direction. At low stations the
maximum velocity occurs at the time of the highest temperature, while
at high stations the reverse obtains. Hill has examined into an
important point connected with this subject, that is, the great local
differences in the vertical variation of temperature. Hill concludes by
saying that high pressures at low levels are the result of low
temperatures, and in connection with the fact that wind directions are
largely influenced by the irregular distribution of pressure at high
levels, it is more important to know the abnormal variations of
pressure at the highest hill stations in India than those in the
plains.
Overbeck has lately published a paper on the apparent motions of the
atmosphere, in which he clearly and admirably outlines the treatment of
the dynamics of the air by his predecessors. He comments on the mode of
treatment of Ferrel, as well as those of Guldberg and Mohn. Overbeck
then sets forth his own method, and elaborately discusses the influence
of the earth's rotation with reference to the resistances which oppose
the motion of the atmosphere. He touches on the effect produced by
rapidly moving fluid entering fluid at rest, the development of
discontinuous (so called by Helmholtz) currents, the tendency of
parallel currents of unequal velocities towards similar velocities, the
effect of friction arising from contiguous currents of different
velocities, upon the coefficient of friction, of the temperature
distribution over the surface of the earth, etc. He derives three very
simple expressions for the motions of the air; the first giving the
velocity in a vertical direction at any point, in terms of latitude,
and a constant and factor depending on the distance of the point above
the surface of the earth. The other expressions give the velocities in
a north or south direction, and in an east or west direction, also in
terms of constants and latitude. The velocity when charted from
Overbeck's equations indicate an ascending vertical current from the
equator to 35° north, and thence a descending current to the pole. The
meridional current at the equator and pole are zero, and have a maximum
value at latitude 45°.
Ciro Ferari, from long and important investigations of thunder storms,
shows that these phenomena invariably attend motionless areas of low
pressure, and believes the surest elements for predicting such storms
will be found to be the peculiarities in distribution of temperature
and absolute humidity. He observes that the storm front invariably
tends to project itself into the regions where the humidity is
greatest, and that hail accompanies rapidly moving storms of deep
barometric depression. Ferari considers the chief causes of thunder
storms to lie in the connection of high temperature and high humidity.
Grossman believes that ascending moist-laden currents are the cause of
thunder storms, and hence they are most frequent when the temperature
diminution with altitude is very great, so that the over-heating of the
lower air strata in the warmest part of the day is the cause of the
primary maximum of thunder-storm frequency.
Abercromby and Hildebrandsson have renewed their recommendations for a
re-classification of clouds in ten fundamental types, in which the
first part of the compound name, such as cirro-stratus, cirro-cumulus,
etc., is to be in a measure indicative of the height of a cloud.
Hildebrandsson has charted the differences of monthly means of air
pressure for January, 1874 to 1884. In January, 1874, the values at
nearly all the stations in the Northern Hemisphere, were plus, and
those in the Southern, minus. It is to be hoped that such general
discussions of this important meteorological element may be continued.
General A. Von Tillo has determined, by means of the planimeter, the
distribution of temperature and pressure from Teisserenc de Bort's
charts. The mean pressure over the Northern Hemisphere for January, he
finds to be 29.99 inches (761.7 millimeters), and the temperature 46°.9
(8°.3 C.); in July, 29.806 (758.5 mm.) and 72°.7 (22°.6 C.). In Russia
he finds an increase of one millimeter of pressure to correspond with a
decrease of 1°.6 C. in temperature.
Doberck, after investigation of September typhoons at Hong Kong,
attributes their appearance to the relatively low pressure then
existing between Formosa and Lyon.
The valuable and elaborate investigation of American Storms, by
Professor Elias Loomis has been completed. Loomis has thoroughly
discussed barometric maxima and minima areas as presented by the maps
of the Signal Service, from which it appears that these areas are in
general elliptical, with the longest axis nearly twice that of the
shortest in the high areas, while the difference is less in low areas.
He has also investigated the winds relative to baric gradients, thus
affording valuable data for proving various meteorological theories.
Loomis' researches regarding the movement of maximum areas verify those
which have been set forth from time to time in Signal Service
publications; wherefrom it appears that high areas have a more
southerly movement than low areas.
Van Bezold has put forth a memoir on thermodynamics, while Helmholtz,
Oberbeck, and Diro-Kitso have contributed valuable memoirs on motions
caused by gravitation and the varying density of the air. These furnish
meteorologists with important results as to the laws of fluid or
gaseous motions. It is gratifying to Americans to note that the
valuable results obtained by Ferrel in his many memoirs are confirmed
by these later investigations.
Undoubtedly the most important meteorological event within the past
year was the discontinuance, on January 1, 1888, of the system of
International Simultaneous Meteorological reports inaugurated in
accordance with the agreement of the conference at Vienna in September,
1873. As the charts of storm tracks, based on these observations, have
been published by the United States Signal Service one year behind the
date of the observations, the completion of this work in printed form
for the general public should occur about December 31, 1888.
A few remarks in connection with this unparalleled set of observations
may not be out of place. The congress which agreed upon this work, met
in accordance with invitations issued by the Austrian Government in
September, 1873. The co-operation decided upon at this congress took
practical shape January 1, 1874, at which date one daily simultaneous
report was commenced from the Russian and Turkish Empires, the British
Islands, and the United States: the energetic co-operation of these
nations being assured through Professor H. Wild for Russia; Professor
A. Coumbary for Turkey; Mr. Robert H. Scott for Great Britain; and Bvt.
Brig. General A. J. Meyer, for the United States. Concurrent action
followed shortly after on the part of Austria, through Professor Carl
Jelinek; Belgium through Professor E. Quetelet; Denmark through Capt.
Hoffmeyer; France through Monsieurs U. J. Leverrier, Marie Davy, and
St. Claire Deville; Algiers by General Farre; Italy by Professor
Giovanni Cantoni; the Netherlands by Professor Buys Ballot; Norway by
Professor H. Mohn; Spain by Professor A. Aquilar; Portugal by Professor
F. de Silveira; Switzerland by Professor E. Plantamour; and the
dominion of Canada by Professor G. T. Kingston. Within a year the
average number of daily simultaneous observations made outside the
limits of the United States increased to 214. Later, the co-operation
of the Governments of India, Mexico, Australia, Japan, Brazil, Cape
Colony, Germany, and Greece, was obtained, and also of many private
observatories at widely separated points throughout the Northern
Hemisphere.
In the sixteen years during which simultaneous meteorological
observations were continued, reports were received from nearly fifteen
hundred different stations, about one-half being from land stations,
and the others from vessels of the navies and the merchant marine of
the various countries.
The total number of storm centers, counting one for each 5-degree
square over which the centre has been traced from the International
Simultaneous observations of 1878 to 1887, inclusive, aggregates over
forty-two thousand, an annual average of over four thousand two
hundred. Less than 1/25 of 1 per cent. of these storms occurred south
of the parallel of 10°, and only ¼ of 1 per cent. south of the parallel
of 15°. In marked contradistinction to this freedom of the equatorial
regions from storms, there is to be noted the excessive prevalence of
these phenomena between the parallels of 40° and 60°, north; in which
regions substantially two-thirds of the storms of the Northern
Hemisphere occurred; while between the parallels of 45° and 55°, north,
36 per cent. of the entire disturbances are recorded. The most
remarkable belt of storm frequency on the Northern Hemisphere is that
extending from the Gulf of Saint Lawrence westward to the extreme end
of Lake Superior, as nearly 8 per cent. of all the storms of the
Northern Hemisphere passed over this limited region; the maximum
frequency (1.2 per centum) occurring over the 5-degree square
northeastward of Lake Huron.
As regards longitudinal distribution, an unusually large proportion of
storms prevailed between the 50th meridian and 105th meridian, west; 37
per cent. or one-third of all the storms of the Northern Hemisphere
occurring within this region. A second belt of comparative storm
frequency obtains from the meridian of Greenwich eastward to the 30th
meridian; over which region 15 per cent. of the entire number of storms
occurred.
Only four hundred, or less than 9 per cent. of the entire number of
storms, entered the American continent from the Pacific ocean, while
about thirteen hundred storms, excluding the West India hurricanes,
passed eastward off of the American continent. Over nine hundred storms
entered Europe from the Atlantic ocean, of which probably four hundred
and fifty, or ten per cent. of the whole number recorded, were
developed over the Atlantic ocean. Probably not thirty storms, or less
than three per cent. of those which entered Europe from the Atlantic,
crossed over the continents of Europe and Asia to the Pacific ocean.
Fully two-thirds of the storms which enter Europe from the Atlantic are
dissipated as active storm-centres before they reach the Asiatic
frontier.
The tendency of great bodies of water, when surrounded wholly or
largely by land, to generate storms or facilitate their development, is
evident from the unusual prevalence of storms over the great lakes, the
St. Lawrence bay and the Gulf of Mexico in North America; over the
North and Baltic seas, Bay of Biscay and the Mediterranean in Europe;
the Bay of Bengal, and over the China and Okhotsk seas.
Undoubtedly a considerable proportion of these storms are drawn towards
these regions owing to the effect of evaporation upon the humidity and
temperature of the superincumbent atmosphere, so that a very
considerable proportion of the storms credited to these squares have
not originated therein, but have been drawn up from neighboring
quarters. This tendency is marked in North America, as storms pass over
the lake region and St. Lawrence valley, whether they have originated
in the Gulf of Mexico, along the central slope of the Rocky mountains
in the United States, or further north in the Saskatchewan country. In
like manner storms pass southeastward to the Mediterranean from the Bay
of Biscay, and northeastward from the Atlantic ocean to the same sea,
and then later show a very marked tendency to pass over the Black and
Caspian seas.
This tendency of storms originating in diverse sections to move toward
the lake regions in the United States, is very evident from the normal
storm-track charts for April, May, June, August, November and December.
The opinion that gales rarely, if ever, occur upon the equator is
confirmed by these storm-tracks. The most southern storm in the North
Pacific ocean, developed in July, 1880, between the Island of Borneo
and Mindanao, an excellent account of which is given by Père Mark
Dechevrens, S. J., in the Bulletin Mensuelle of Zi-Ka-Wei Observatory.
The most southern storm over the North Atlantic ocean, in November,
1878, was remarkable for its origin, duration, length of its path, and
its enormous destruction of life and property. It was central on the
1st, as a violent tropical hurricane near Trinidad, the barometer being
29.05, the lowest ever recorded there, and, from its intensity and
velocity, it is more than probable that it originated considerably to
the eastward, and possibly somewhat to the southward of that island.
The storm was described in the U. S. Monthly Weather Review for
September, 1878.
The writer looks with considerable interest to the results which may
follow from a discussion of the annual fluctuation of the atmospheric
pressure as shown by the mean monthly pressures deduced from the ten
years' International observations. As far as these means have been
examined they show that the periodicity of atmospheric pressure is
largely in accord with the results set forth in 1885 in The Report of
the Lady Franklin Bay Expedition. The conviction expressed in that year
is still adhered to--that, at no distant day, the general laws of
atmospheric changes will be formulated, and that later, from abnormal
_barometric departures_ in remote regions may be predicted the general
character of seasons in countries favorably located.
The success of long-time predictions of this class for India, has been
set forth in a previous part of this report. It is believed that a
further discussion of meteorological phenomena on a broad basis, by
means of International Weather Charts, both in daily and monthly form,
must eventually result in important and fundamental discoveries. It is
gratifying to American pride to know that in this international task of
outlining the geography of the air, the United States has liberally
provided the labor and means for presenting these ten years'
meteorological data in such tabular and geographical forms as to render
them available for study by all.
Acknowledgment is due to Professor Thomas Russell, for valuable
translations, especially from the German; which translations have been
of material value in preparing this report.
December, 1888.