KITES--HISTORY AND APPLICATION TO METEOROLOGICAL PURPOSES AT
BLUE HILL AND ELSEWHERE
Kites are supposed to have been invented four hundred years before the
Christian era by Archytas, and at Smyrna the flying of kites remains a
national sport to this day. We are told that two hundred years later,
a Chinese general, Han Sin, employed kites as a means of communication
with the garrison of a besieged town, and there is a legend about
their use in Japan to dislodge and carry away a golden ornament from a
tower. Whatever may be the truth of these stories, we know that
kite-flying in the Malay Archipelago, in China, and in Japan, has been
a pastime for all classes during centuries, and that the Asiatic
people have always been the expert kite-fliers of the world.
Kites with tails seem to have been introduced into England about two
hundred and fifty years ago, and Isaac Newton when a school-boy made
some improvements in them. Notwithstanding the fact that generations
of boys have flown kites and so eminent a mathematician as Euler
investigated their theory, until recently kites remained toys unsuited
for practical purposes. Since the tailless kite has become a familiar
object, it has been said facetiously that kites lost their tails by
the same process of evolution which deprived man of his caudal
appendage; but as kites without tails have been flown in Asia for
centuries, the truth is that the tailed kites were the ones first
brought to Europe as playthings. To-day in Holland we see boys flying
the English bow-kite and the common kite with crossed sticks, both of
which require tails, and by the side of them tailless kites imported
from the Dutch colonies in Java. Fig. 7 represents a kite from the
east coast of Java, drawn from a model in a museum at Amsterdam, and
also a drawing of a Chinese bird-kite in the National Museum at
Washington. Like most of the oriental kites, they are made flat, but
when exposed to the wind the extremities of the wings, which have a
frame of split bamboo, bend backward, securing in this way the
stability which in our common flat kite is gained by the action of the
tail in lowering the centre of gravity and in maintaining the
inclination to the wind.
[Illustration: FIG. 7.--Oriental tailless Kites.]
From historical researches that have been stimulated by the recent
practical applications of kites, it appears that their first use for
scientific purposes was in 1749, when Dr. Alexander Wilson of Glasgow,
and his pupil, Thomas Melvill, used kites to lift thermometers. Their
kites, from four to seven feet in height, and covered with paper, were
fastened behind one another, each kite taking up as much line as could
be supported, thereby allowing its companion to soar to an elevation
proportionally higher. It is related that "the uppermost one ascended
to an amazing height, disappearing at times among the white summer
clouds, whilst all the rest, in a series, formed with it in the air
below such a lofty scale, and that too affected by such regular and
conspiring motions, as at once changed a boyish pastime into a
spectacle which greatly interested every beholder.... To obtain the
information they wanted they contrived that thermometers, properly
secured, and having bushy tassels of paper tied to them, should be let
fall at stated periods from some of the higher kites, which was
accomplished by the gradual singeing of a match-line." How the
thermometers were prevented from changing their readings while falling
to the ground is not explained. The account concludes: "When engaged
in these experiments, though now and then they communicated
immediately with the clouds, yet, as this happened always in fine
weather, no symptoms whatever of an electrical nature came under their
observation. The sublime analysis of the thunderbolt, and of the
electricity of the atmosphere, lay yet entirely undiscovered, and was
reserved two years longer for the sagacity of the celebrated Dr.
Franklin." Hence it seems that Franklin's famous experiment of
collecting the electricity of a thunder-cloud by means of a kite,
performed at Philadelphia in 1752, was not its first scientific
application, and therefore America can claim only the later and most
remarkable development of this means of exploring the air.
About 1837 there existed in Philadelphia an organization called the
Franklin Kite Club that flew kites for recreation. Espy, the eminent
meteorologist, was a member, and he states "that on those days when
columnar clouds form rapidly and numerously the kite was frequently
carried upward nearly perpendicularly by columns of ascending air," a
phenomenon which is often observed to-day. Espy calculated the height
at which clouds should form by the cooling of the air to its
dew-point, and then employed kites to verify his calculations of the
heights of the clouds. It will be remembered that both these methods
are utilized in the measurements of cloud-heights at Blue Hill. Kites
were employed to get temperatures a hundred or more feet above the
Arctic ocean early in the present century, and in 1847 W. R. Birt flew
a kite at Kew Observatory, with which he hoped to obtain measures of
temperature, humidity, wind velocity, etc. This kite, hexagonal in
shape, required three divergent strings attached to the ground to keep
it steady, and the instruments were to be hoisted up to the kite by a
pulley.
Perhaps the first person to soar aloft on a kite was a lady, who, more
than fifty years ago, was lifted some hundred feet by a great kite
constructed by George Pocock, an Englishman, to serve as an aÎrial
observatory in warfare, and also to drag carriages along the ground.
It was proposed afterwards to make use of kites in shipwrecks to take
persons or life-lines ashore, and in 1865 Sir George Nares invented a
storm-kite, so called, with a tail made up of hollow cones. This form
of tail, subsequently used for both kites and balloons, is very
efficient, since it offers increasing resistance as the wind becomes
stronger.
In 1882 Mr. Douglas Archibald in England revived the use of kites for
meteorological observations, and outlined a comprehensive scheme of
exploring the air with kites which included almost all that has been
done since, but his actual work, performed during the next three
years, was limited to ascertaining the increase of wind velocity with
height. To do this, he attached registering anemometers at four
different points on the kite-wire, but since the total wind movements
only were registered from the time the anemometers left the ground
until they returned, it was impossible to obtain simultaneous records
near the ground and at the kite, as is done to-day. Still, Archibald
got differential measurements of the velocity of the wind up to the
height of 1200 feet. The kites he employed were diamond-shaped,
covered with silk, and were flown tandem, with the hollow cones,
already mentioned, attached to the tails. Although copper and iron
wire had been used for flying kites many years before, yet Archibald
was the first to substitute steel pianoforte wire for the string,
thereby increasing the strength while diminishing the weight, size,
and cost of the line. Mr. Archibald in 1887 took the first photograph
from a kite, a method which MM. Batut and Wenz developed in France,
and Messrs. Eddy and Woglom in the United States.
The subsequent progress of kite-flying for meteorological purposes has
taken place in the last-named country, and may be chronologically
stated as follows: in 1885 Mr. Alexander McAdie (later of the U. S.
Weather Bureau) repeated Franklin's kite experiment on Blue Hill, with
the addition of an electrometer; in 1891, and again in 1892, he
measured simultaneously the electric potential at the base of Blue
Hill, on the hill, and with kites as collectors several hundred feet
above the hill-top, about the same time that Dr. Weber, in Breslau,
Germany, was making a more extensive use of kites for the same
purpose. It was no doubt William A. Eddy of Bayonne, N. J., who turned
the attention of American scientific men to kite-flying, and created
the widespread interest in kites which exists to-day. About 1890 Mr.
Eddy lifted thermometers with an ordinary kite, but soon afterwards
devised a tailless kite, resembling the Java kite except that the
horizontal cross-piece is nearer the top of the vertical stick, and
its ends are bent backward in a bow and connected by a cord. This kite
starts upward on being held in the wind at the end of a taut line, and
continues to rise until the increasing wind-pressure on the portion
above the cross-stick balances the pressure on the larger lower
portion. The kite is kept from falling to one side by the looseness of
the covering on either side of the backbone, and if there is more
material on one side than on the other, or if the covering is too
tight to form pockets in the wind, the kite requires a tail.[1]
[1] A tail will prevent any kite from turning over, or "diving,"
because its weight keeps the lower end down while the
pressure of the wind on the tail also pulls the lower end
backward and maintains the necessary angle of the kite to the
wind, the most efficient angle being about 22 degrees. Bending
back the ends of the cross-stick gives stability to a kite
because, when, on account of the eddies in the wind, a stronger
pressure is exerted on one side of the kite, this side is
driven backward, thereby presenting less effective surface to
the wind, while as the other side comes forward more nearly at
right angles to the wind, it receives greater pressure than
before. In this way the equilibrium about the central stick is
automatically maintained, the required inclination to the wind
being secured by the greater surface presented to the wind
below the point of attachment of the bridle.
In 1891 Mr. Eddy lifted a minimum thermometer by several of these
kites flown tandem, and proposed to obtain in this way data to
forecast the weather. In the _Proceedings of the Aeronautical
Conference_, held in connection with the Chicago Exposition, Prof. M.
W. Harrington, then Chief of the U. S. Weather Bureau, quoted Mr.
Eddy's estimate of the cost of exploring the air by means of kites
flown in series, and advocated their use.
Up to this time it does not appear that self-recording
instruments--that is to say, those which make continuous graphic
records--had been raised by kites. In the days of the early
experimenters such instruments were too heavy and cumbersome to be
lifted by the more or less unmanageable kites, but within the past few
years M. Richard of Paris has made the simple and light recording
instruments described in connection with balloons, which can be
attached to kites. In this way it is possible to obtain simultaneous
records at the kite and at a station on the ground, and from them to
study the differences of temperature and humidity, and this seems to
have been done first at Blue Hill Observatory. In August 1894 Mr. Eddy
brought his kites to Blue Hill and with them lifted a Richard
thermograph, which had been partly reconstructed of aluminium by Mr.
Fergusson so that it weighed but 1-1/4 lbs., to the height of 1500
feet, and so the earliest automatic record of temperature was obtained
by a kite. During the next summer, Mr. Eddy assisted again in the
experiments at Blue Hill, and secured photographs of the Observatory
and the hill by a camera carried between his kites to the height of a
hundred feet or more.
Now that the possibility of lifting self-recording meteorological
instruments to considerable heights had been demonstrated, an
investigation of the thermal and hygrometric conditions of the free
air was undertaken by the staff of the Blue Hill Observatory, who had
already made an investigation of the movements of the clouds by the
methods described in the second chapter.
The development of the kite and its accessory apparatus, and the
acquisition of the knowledge how to use them, required much time, and
resulted in the damage or loss of many kites. Two meteorographs, as
the combination of two or more self-recording instruments is called,
were dropped from a great height and no trace of them was found. When,
however, by the breaking of the line both kites and instrument are
carried away, the kites act as a parachute and bear the instrument
gently to the ground, where both are usually recovered uninjured; to
facilitate their return should they fall at a distance, the name and
address are marked on each. It would be tedious to relate the ups and
downs of scientific kite-flying at Blue Hill before the wind was
successfully harnessed to the service of science, and the kites were
prevented from kicking over the traces, or from breaking away, so only
a brief account of the progress of the work will be given, and then
the methods at present used will be described. At first the Eddy, or
Malay kites, as they are also called, covered with paper or with
varnished cloth, were coupled tandem to secure greater safety and
lifting power. The principle of attaching kites at several points on
the line was early adopted at Blue Hill, for although it can be
demonstrated theoretically that a greater height is possible by
concentrating all the pull at the end of the line, yet in the case of
a line which is not infinitely strong the best results are got by
distributing the pull, and in this way, too, kites can be added as the
wind conditions aloft warrant. To obviate the frequent breaking of the
bowed cross-piece, Mr. Fergusson made it in two pieces, each being
held in a metal socket on the central stick, the two pieces forming a
dihedral angle towards the wind. It had the advantage also of being
readily taken apart for transportation. This kite, shown in Fig. 8,
flew at a high angle above the horizon and through a considerable
range of wind velocity, but it could not be kept permanently in
balance, or made to adjust itself to great variations in wind
velocity, and therefore it was discarded.
The first meteorograph, a combined recording thermometer and barometer
(from which the height can be calculated), was constructed by Mr.
Fergusson in August 1895, and three months later he united a recording
anemometer to the thermometer, which was probably the first apparatus
of this kind to be attached to kites. A meteorograph, recording the
atmospheric pressure, air temperature, and relative humidity, was
ordered from M. Richard of Paris in 1895, like one already carried by
French aeronauts, except that, since for kites lightness is
all-essential, M. Richard constructed this triple-recorder for the
first time of aluminium, and hereby reduced its weight to 2-4/5 lbs.
[Illustration: FIG. 8.--Eddy tailless Kite.]
[Illustration: FIG. 9.--Hargrave Kite.]
One of these meteorographs was hung to a ring at the point of
attachment of the two kite-lines to the main line, a method which was
used until recently. In August 1895, besides the Eddy kites, there was
first used the cellular or box kite, invented by Lawrence Hargrave of
Sydney, Australia, which bears no resemblance to the conventional
forms of kites and which it would not be supposed could fly. As seen
from Fig. 9 its appearance is that of two light boxes without tops or
bottoms, fastened some distance above each other. The wind exerts its
lifting force chiefly upon the front and rear sides of the top box,
the lower box, which inclines to the rear, and so receives less
pressure, preserving the balance. The ends of the boxes, being in line
with the wind, keep the kite steady and serve the purpose of the
dihedral angle in the Malay kite. The Japanese are said to fly a
single box, which is the prototype of the Hargrave double cell.
At the present time some form of the Hargrave kite is generally
employed for scientific purposes. On account of the weight of the
large cord necessary to control these kites, and the surface which it
presented to the wind, a height of 2000 feet could not be reached, so,
during the winter of 1895-6, following Archibald's example and the
methods of deep-sea sounding employed by Captain Sigsbee, U. S. N.,
steel pianoforte wire was substituted for the cord. This wire is less
than half as heavy, and less than one-fourth the size of cord having
the same strength, and, moreover, its surface is polished, which
reduces the friction of the wind blowing past it. With the wire the
height of a mile was reached in July, and a mile and two-thirds above
Blue Hill in October 1896.
Up to this time a reel turned by two men sufficed to draw down the
kites, but the increasing pull and length of wire made recourse to
steam-power necessary. In January 1897 a grant of money was allotted
from the Hodgkins Fund of the Smithsonian Institution for the purpose
of obtaining meteorological records at heights exceeding ten thousand
feet, and no doubt the first application of steam to kite-flying was
the winch built by Mr. Fergusson with ingenious devices for
distributing, oiling, and measuring the length of wire. The cumulative
pressure of the successive coils of wire finally crushed the drum, and
the next apparatus applied the principle of Sir William Thomson's
deep-sea sounding apparatus, in which there is no accumulation of
pressure. In October 1897 records were brought down from eleven
thousand feet, or a thousand feet above the prescribed height.
The kites and apparatus at present employed at Blue Hill will now be
described.
The kites are all of the multiplane type, and mostly of Hargrave's
construction with two rectangular cells. These cells are covered with
cloth or silk, except at their tops and bottoms, and one is secured
above the other by four or more sticks. The wooden frames are as light
as possible, but are made rigid by guys of steel wire that bind them
in all directions. The average weight is about two ounces a square
foot of lifting surface, which is about the same weight a square foot
as the Eddy kites when all the surface is included in the estimate.
The largest of the Hargrave kites stands nine feet high, weighs eleven
pounds, and contains ninety square feet of lifting surface, which in
the recent kites is arched, resembling the curvature of a bird's
wings, a construction that was proposed many years ago by Phillips
(Fig. 10). These curved surfaces increase the lift, or upward pull,
more than the drift, or motion to leeward, and so the angular
elevation is augmented without materially adding to the total pull on
the wire, which should not exceed one-half its breaking strength.
[Illustration: FIG. 10.--Modified Hargrave Kite at
Blue Hill.]
Perhaps the most important factor in the success of the Blue Hill work
was the invention by Mr. Clayton of the regulating bridle which is
applied to every kite. An elastic cord is inserted in the lower part
of the bridle, to which the flying-line is attached, and when the
wind-pressure increases this cord stretches, and causes the kite to
diminish its angle of incidence to the wind until the gust subsides. A
kite can be set to pull only a fixed amount in the strongest wind,
when the kite will fly nearly horizontal. We are therefore able to
calculate the greatest pull which can be exerted on the wire by all
the kites. With this device the kites have flown through gales of
fifty or sixty miles an hour without breaking loose or injuring
themselves. Another efficient kite which has been used at Blue Hill is
the so-called "aero-curve kite" made by Mr. C. H. Lamson of Portland,
Maine. As is seen from Fig. 11, this kite resembles a soaring bird,
and it can be taken apart and folded up for storage or transportation.
In general, the angle of the flying lines of the Blue Hill kites is
50∞ or 60∞ above the horizon, and in winds of twenty miles an hour the
pull on the line is about one pound for each square foot of lifting
surface in the kite. Kites can be raised in a wind that blows more
than twelve miles an hour at the ground, and as the average velocity
of the wind for the year on Blue Hill is eighteen miles an hour, the
days are few when kites will not fly there.
[Illustration: FIG. 11.--Lamson's Aero-curve Kite.]
The wire to which the kites are attached is steel music-wire, 32/1000
of an inch in diameter, weighing fifteen pounds a mile, and capable of
withstanding a pull of three hundred pounds. The wire is spliced in
lengths of more than a mile with the greatest care, special pains
being taken that no sharp bends or rust-spots occur which would cause
it to break. To lift the increasing weight of wire, kites are
attached at intervals of a few thousand feet, so that the angle may be
maintained as high as is consistent with a safe pull, and this is done
by screwing on the wire aluminium clamps, to which the kite-lines are
fastened. On account of the greater stability and strength of the new
kites, the meteorograph is suspended directly from the top kite. The
Richard meteorograph, contained in an aluminium cage of about a foot
cube, weighs less than three pounds, and it is only necessary to
screen the thermometer from the sun's rays to obtain the true
temperature of the air, since the wind insures a circulation of air
around the thermometer. Another meteorograph, constructed by Mr.
Fergusson, records the velocity of the wind in addition to the three
other elements, and it weighs no more than the French instrument.
The reeling apparatus is an example of how the same apparatus may
serve diametrically opposite purposes. In sounding the deep sea the
wire must be pulled upwards, whereas in sounding the heights of the
atmosphere the wire must be pulled in the reverse direction. Therefore
the deep-sea sounding apparatus has been altered by Mr. Fergusson to
pull obliquely downwards, the wire passing over a swivelling pulley
which follows its direction and registers on a dial the exact length
unreeled. Next the wire bears against a pulley carried by a strong
spiral spring, by which the pull upon it at all times is recorded on a
paper-covered drum turned by clockwork. The wire passes now several
times around a strain-pulley, and finally is coiled under slight
tension upon a large storage-drum. When the kites are to be pulled
down, the strain-pulley is connected with a two-horse-power
steam-engine, and the wire is drawn in at a speed of from three to six
miles an hour; but when the kites are rising the belt is removed, and
the pull of the kites unreels the wire.
[Illustration: FIG. 12.--Meteorograph lifted by Kites
at Blue Hill.]
The method of making a kite-flight for meteorological purposes at Blue
Hill is as follows: a kite, fastened by a long wire to the ring in the
main wire, being in the air, and the meteorograph suspended, another
kite is attached to the ring by a shorter cord (Fig. 12). They are
then allowed to rise, and to unreel the wire, until its angle with the
horizon becomes low, when, by means of the clamps described, other
kites are added, the number depending on the size of the kites and the
strength of the wind. After a pause at the highest attainable
altitude, the winch is connected with the steam-engine and the kites
are drawn down. The pauses at the highest point, and when kites are
attached or detached, are necessary to allow the recording instruments
to acquire the conditions of the surrounding air; and because at
these times the meteorograph is nearly stationary, measurements of its
angular elevation are made with a surveyor's transit, while
observations of azimuth give the direction of the wind at the
different heights. The time of making each angular measurement is
noted, so that the corresponding point on the trace of the
meteorograph may be found. From the length of the wire and its
vertical angle, the height of the meteorograph can be calculated, it
having been found that the sag of the wire, or its deviation either in
a vertical or a horizontal plane from the straight line joining the
kite and the reel, does not cause an error exceeding three per cent.
in the height so computed. When the meteorograph is hidden by clouds,
the height above the last point trigonometrically determined is
computed from the barometer record by Laplace's formula. At night
there is only the barometer from which to determine the height; for
although an attempt was made to use a lantern to sight upon, yet it
soon became invisible, or, when seen, was confounded with the stars.
Before and after the flight the meteorograph is hung upon a tripod in
the free air, in order that its thermometer and hygrometer may be
compared with the standards.
HEIGHTS ABOVE SEA-LEVEL OF KITE-FLIGHTS.
(_Blue Hill is 630 feet above the sea_)
----+----+----------------++-------------------------------------------
| No.|Heights in Feet || Percentages of Records above
Year| of +-------+--------++-------+--------+--------+--------+--------
|Rec-|Mean of|Absolute|| 500 m.| 1000 m.| 1500 m.| 2000 m.| 3000 m.
|ords|Maximum|Maximum || (1640 | (3280 | (4920 | (6560 | (9840
| | | || ft.) | ft.) | ft.) | ft.) | ft.)
----+----+-------+--------++-------+--------+--------+--------+--------
1894| 2 | 1,860 | 2,070 || 50 | 0 | 0 | 0 | 0
1895| 28 | 1,673 | 2,490 || 59 | 0 | 0 | 0 | 0
1896| 86 | 2,772 | 9,327 || 78 | 28 | 9 | 4 | 0
1897| 38 | 4,557 | 11,716 || 95 | 68 | 45 | 21 | 5
1898| 35 | 7,350 | 12,070 || 100 | 92 | 80 | 66 | 20
----+----+-------+--------++-------+--------+--------+--------+--------
Since the use of wire and more efficient kites, the heights have been
greatly increased. Thus the average height above the hill attained by
the meteorograph in thirty-five flights made during 1898 was more than
a mile and a quarter, whereas the average height of all the ascents
prior to 1897 was about a quarter of a mile (see Table). The average
height of the meteorograph above the hill, in all the flights during
August 1898, was nearly a mile and a half, and on August 26 the
meteorograph was raised 360 feet higher than ever before, its
altitude, determined trigonometrically, being 11,440 feet above Blue
Hill, or 12,070 feet above the neighbouring ocean. The meteorograph
was suspended from the topmost kite, one of the Lamson pattern, having
71 square feet of lifting surface, and this was increased to a total
of 149 square feet by four kites of the modified Hargrave type, that
were attached at intervals to the wire. The five miles of wire in the
air weighed 75 lbs., and the total weight including kites and
apparatus was 112 lbs. The meteorograph left the ground at 10:40 a.m.,
attained its greatest height at 4:15 p.m., and returned to the ground
at 8:40 p.m., a feat which it would be difficult for a man to equal on
a mountain. The cumulus clouds were traversed three-quarters of a mile
from the earth, and above them the air was found to be very dry. On
the hill the air temperature was 72∞, when it was 38∞ in the free air
11,440 feet above, and the wind velocity increased from twenty-two to
forty miles an hour. These figures give an idea of the change of
atmospheric conditions which occurs, but the conclusions deduced from
the Blue Hill kite-flights will be discussed in the next chapter.
However, the phenomena of atmospheric electricity, which have become
noticeable since the use of wire, may be described here. Generally,
whenever the kites rise above seventeen hundred feet, the wire becomes
strongly charged with electricity, and when the great heights are
reached the electricity is discharged in long and brilliant sparks at
the reel, often to the inconvenience of the attendants. Usually, the
electrical potential increases with altitude, and it is greatest
during snow-storms or when the conditions favour thunder-storms.
Notwithstanding its intensity, the quantity of electricity in the
atmosphere is probably insufficient to make its collection and
storage for practical purposes worth while.
It must not be imagined that kite-flying for meteorological purposes
is a sinecure. At Blue Hill about two hundred flights have been made
in all seasons and in all weathers, with temperatures varying from
-5∞ to +90∞, in gales, in rain, and in snow-storms, though not in
thunder-storms. Sometimes the kites are invisible from almost the time
they leave the earth until their return, but when the upper kites are
visible it is necessary to observe them with theodolites every few
minutes. Remembering that a high flight occupies ten or twelve hours,
and frequently terminates late at night, or even continues until
morning, it will be obvious that the work requires skill, energy, and
perseverance, which have been shown by my assistants at the Blue Hill
Observatory who have conducted the flights.
Occasionally, for lack of wind or from breakage of the line, the kites
fall to the ground, usually intact. If they were visible,
trigonometrical measurements on the hill enable the place of descent
to be located, and then the kites and meteorograph are sent for and
the wire is reeled up. But at night, or when clouds hide the kites,
the direction in which they fall is not known, because the azimuth of
the wire at the reel often differs from that of the kites; so last
autumn several hundred miles of road, path, wood, and swamp were
traversed before the aÎrial apparatus, which had been lost during a
flight at night, was found comparatively close at hand.
From what has been said it will be evident that a former toy has been
proved to be of the greatest importance for meteorological
investigation at the Blue Hill Observatory. On account of the success
there attained it is coming into use elsewhere for meteorological
observations. In 1898 the United States Weather Bureau created
seventeen kite stations, chiefly in the Mississippi Valley, with the
intention of obtaining data every day, at the height of a mile or
more, with which to plot a synoptic weather map similar to the map
that is now drawn from the data at the ground. From a knowledge of the
weather conditions prevailing simultaneously in the upper and lower
air, it was expected that the weather forecasts could be improved, but
unfortunately, on account of the light winds during the summer, it was
impossible to make enough simultaneous kite-flights to construct the
upper-air map, and therefore the scheme was abandoned. However, the
data obtained will no doubt furnish valuable information about the
vertical temperature gradient, etc., in various conditions of weather.
The chief meteorological bureaus of Germany and Russia are equipping
stations with kites and balloons, and M. Teisserenc de Bort, who has
provided his private observatory near Paris with kite apparatus of the
Blue Hill type, has already reached high altitudes. In Scotland too,
which was the birthplace of scientific kite-flying, experiments have
been resumed by a Scotchman and an American--a happy union of forces.
From these preparations it appears that the resolution of the
International Aeronautical Conference, recommending that all central
observatories should employ this method of investigation as being of
prime importance for the advancement of meteorological knowledge, is
being carried out, and seems likely to produce important results.