OCEAN WEATHER MAP PREPARED FROM VESSEL REPORTSJAN. 11, 1913, GREENWICH MEAN NOONU. S. Weather BureauSolid black lines are isobars. Arrows fly with the wind, the center of the arrowhead marking the position of the vessel, and the number of feathers denoting the force of the wind on the Beaufort scale. Shading of the head shows degree of cloudiness.
OCEAN WEATHER MAP PREPARED FROM VESSEL REPORTSJAN. 11, 1913, GREENWICH MEAN NOONU. S. Weather Bureau
OCEAN WEATHER MAP PREPARED FROM VESSEL REPORTS
JAN. 11, 1913, GREENWICH MEAN NOON
U. S. Weather Bureau
Solid black lines are isobars. Arrows fly with the wind, the center of the arrowhead marking the position of the vessel, and the number of feathers denoting the force of the wind on the Beaufort scale. Shading of the head shows degree of cloudiness.
Most of the material used in the preparation of the charts above described is obtained from a great corps of volunteer marine observers, who enter theirobservations at stated hours in forms provided for the purpose and send these records to the establishment in charge of the work at the end of each voyage. The forms furnished by the United States Weather Bureau prescribe only one regular observation a day, to be taken at Greenwich mean noon. Each observation shows the position of the ship, the direction of the wind, the force of the wind on the Beaufort scale, the height of the barometer, the readings of the dry-bulb and wet-bulb thermometers, the temperature of the water at the surface, the state of the weather, and the kind, amount, and movement of clouds. In order to check the accuracy of the barometric readings, the observer is instructed to read his barometer at prescribed hours on three successive days when in port and send the readings to the Weather Bureau. On receipt of these readings the Bureau compares them with those of the nearest meteorological station, and then mails the observer a “barometer tag,” showing the results of the comparison and the error of his instrument. Besides keeping up these routine observations, the observer keeps a record of fog encountered at any hour of the day and makes detailed reports on storms. Many marine observers also report observations at stated hours by wireless telegraphy.
The enormous fund of information thus collected over the ocean is applied to several purposes besides the construction of Pilot Charts. Our Weather Bureau and certain foreign meteorological institutions prepare daily charts, showing approximately the instantaneous conditions over great oceanic areas, especially the North Atlantic. These maps are analogous to the daily weather maps published for land areas, but the drawing of each map is, necessarily,delayed for several months after the date to which it refers, in order to allow time for the receipt of as many reports as possible from ships at sea. As a rule such charts are prepared in manuscript only, but, though they cannot be distributed after the manner of ordinary weather maps, they are valuable for studies in the institution itself on the movements of storms and other atmospheric processes. They also enable the meteorological officials to answer inquiries concerning the winds and weather that have prevailed over a particular part of the ocean on any specified date. Such inquiries come from vessel owners, underwriters, and others, and the replies are frequently used as evidence in admiralty suits.
In the case of one series of such maps—viz., the daily synoptic charts of the North Atlantic, begun by Niels Hoffmeyer, of Copenhagen, and now prepared jointly by the Danish Meteorological Institute and the Deutsche Seewarte, in Hamburg—the charts have actually been published and sold, though they are so costly that the number of sets in libraries throughout the world is probably small. These remarkable charts present daily pictures of the winds and barometric pressure over the North Atlantic Ocean and the adjacent continents from 1873 to 1876, and from 1880 down to a recent date.
From what we have already said it will be seen that the marine observers cooperating with the United States Weather Bureau and kindred institutions abroad are all contributing toward the great task of recording the history of the weather over the oceans from day to day and assembling data that can be digested in the form of marine climatic statistics and used as the basis for many scientificinvestigations. This concerted undertaking does not, however, constitute the whole scope of marine meteorology. Every intelligent mariner finds it necessary to acquaint himself with the laws of the winds, indications of coming storms, means of determining the proximity of icebergs, the systems of storm signals used in different countries, the method of constructing weather maps from wireless bulletins, etc. He ought, in short, to become an accomplished meteorologist.
One of the classic problems of the navigator is that of handling his ship in a violent cyclonic storm, especially a tropical hurricane. The reader will recall that a cyclone, besides traveling as a whole at a rate of several hundred miles a day, consists of a system of winds rotating around the center. The result of this double motion is that the winds on one side of the center are not only more violent than those on the other, but they are also so directed as to drive a vessel running before the wind, across the storm track ahead of the advancing center, while those on the other side tend to drive a vessel to the rear of the storm. The two halves of the storm area are accordingly known as the “dangerous” and “navigable” semicircles, respectively. While this simple statement sets forth the fundamental facts involved, the actual problem is complicated by many features, such as the fact that the winds do not blow in circles, but more or less spirally, that the area of the storm cannot be readily determined, that two storms may occur in close proximity to each other, etc.
The accompanying diagram, published by the United States Hydrographic Office, represents a cyclonic storm in the northern hemisphere, thecircles being isobars, or lines passing through places at which the same barometric pressure prevails (indicated in inches), and the arrows indicating the direction of the winds. The diagram is thus explained:
“For simplicity the area of low barometer is made perfectly circular and the center is assumed to be ten points to the right of the direction of the wind at all points within the disturbed area. Let us assume that the center is advancing about north-northeast, in the direction of the long arrow, shown in the heavy full line. The shipahas the wind at east-northeast; she is to the left of the storm track, or technically in the navigable semicircle. The shipbhas the wind at east-southeast and is in the dangerous semicircle.***A vessel hove to at the position markedb, and being passed by the storm center, will occupy successive positions in regard to the center frombtob4, and will experience shifts of the wind, as shown by the arrows, from east through south to southwest. On the other hand, if the storm center be stationary or moving slowly and a vessel be overtaking it along the line fromb4 tob, the wind will back from southwest to east, and is likely to convey an entirely wrong impression as to the location and movement of the center. Hence it is recommended that a vessel suspecting the approach of proximity of a cyclonic storm should stop for a while until the path of the center is located by observing the shifts of the wind and the behavior of the barometer.”
The movement of the winds around the storm center shown in this diagram is that of cyclones of the northern hemisphere; i. e., contrary to the direction of the clock hands. In the southern hemispherethey blow in the opposite direction around the center.
NAVIGATION OF A SHIP IN A CYCLONIC STORM(U. S. Hydrographic Office.)
NAVIGATION OF A SHIP IN A CYCLONIC STORM(U. S. Hydrographic Office.)
NAVIGATION OF A SHIP IN A CYCLONIC STORM
(U. S. Hydrographic Office.)
By observing the rise or fall of the barometer, the shift of the winds, and the state of the sea and sky, the experienced navigator is generally able to lay down on a chart the approximate position of the storm center and steer his vessel so as to avoid danger. Various devices, known as “storm cards,” “cyclonoscopes,” etc., have been used to aid in the process of locating a storm from shipboard observations. In the Far East mariners use for locatingtyphoons an ingenious combination of the storm card and the aneroid barometer, called the “barocyclonometer,” an invention of the Rev. J. Algué, director of the Philippine Weather Bureau.
The most important development in marine meteorology in recent years has been the rapidly increasing use of radiotelegraphy, both by marine observers in transmitting reports of observations to shore and to other ships, and by meteorological institutions in issuing weather bulletins and storm warnings to vessels at sea. The first regular undertaking in this line was carried out under the auspices of the LondonDaily Telegraphin the year 1904. This newspaper arranged with some of the leading transatlantic steamship lines to furnish weather reports by wireless from their vessels, and these reports were published in its columns for several months. The following year the United States Weather Bureau began, in a tentative way, the collection of wireless weather reports from off-shore vessels, and similar undertakings were soon afterward launched in other parts of the world, but for some years such reports were of little practical value, owing to the limited range of wireless communication.
A SHIPBOARD WEATHER MAPVessels off the American coast can make their own weather maps every night, using data supplied at fixed hours by high-power radio stations (shown by stars on the map), together with radio reports from other vessels. Letters near stations are the code letters used in wireless bulletins to describe the stations. Vessel reports are indicated by names. Arrows show direction of wind and the force on the Beaufort scale (shown by the number of feathers). Besides data for constructing maps, the radio stations issue forecasts and storm reports for each of the numbered zones shown off the Atlantic coast and over the Gulf.
A SHIPBOARD WEATHER MAP
A SHIPBOARD WEATHER MAP
Vessels off the American coast can make their own weather maps every night, using data supplied at fixed hours by high-power radio stations (shown by stars on the map), together with radio reports from other vessels. Letters near stations are the code letters used in wireless bulletins to describe the stations. Vessel reports are indicated by names. Arrows show direction of wind and the force on the Beaufort scale (shown by the number of feathers). Besides data for constructing maps, the radio stations issue forecasts and storm reports for each of the numbered zones shown off the Atlantic coast and over the Gulf.
At the present time wireless reports from ships on the Atlantic enable the forecasters on both sides of that ocean to extend the areas of the weather maps on which their predictions are based, and reports from ships are also received to a limited extent by forecasters on our Pacific coast as well as in the Far East, India, and elsewhere. In this country such reports have been especially valuable in indicating the movements of West India hurricanes, and thus have helped to solve the problem ofprotecting the vast tonnage that has been attracted to Caribbean waters by the opening of the Panama Canal. The reciprocal process of transmitting weather intelligence to vessels by wireless bulletins, broadcasted at certain hours every day by high-powered radio stations, has made much more progress. Such bulletins include information concerning the current and prospective weather, winds and storms over specified ocean areas, as well as reports of observations made at a number of land stations, from which it is possible for vessels at sea to construct their own weather maps. They are thus enabled to take advantage of favorable winds and to avoid unfavorable winds and storms. Wireless weather reports from other vessels help to piece out these shipboard maps.
The meteorological services of all civilized countries adjacent to the sea display signals along their coasts to announce the coming of storms dangerous to navigation. One of the earliest devices used for this purpose was the “aeroclinoscope,” a form of semaphore formerly employed by the meteorological service of Holland. The position of the arm of the semaphore indicated the region in which the barometer was low; i. e., the storm center. In the British Isles, in the middle of the last century, Admiral FitzRoy introduced the use of canvas cones and “drums” (i. e., cylinders), which, seen from any direction, have the appearance of solid triangles and squares against the background of the sky. The British later abandoned the drum and used the cone only, pointing up or down for northerly or southerly gales, respectively. The American storm flag—red with a square, black center—was adopted by the United States Signal Service (the predecessor of theWeather Bureau) in 1871. This signal was subsequently amplified by the addition of red and white pennants to show the expected direction of the wind at the beginning of the approaching storm. Most countries use lanterns for night storm signals. In the year 1909 a uniform system of signals, consisting of cones by day and lanterns by night, was recommended for use in all countries by an international commission which met in London.
In spite of this recommendation some thirty or forty different systems of daytime storm signals are now in use in different parts of the world. On the China coast an elaborate system of signals, consisting of cones, balls, diamonds, and squares displayed on a mast and yardarms, indicates the existence of a typhoon anywhere in the neighboring seas, together with its location and movement.
Duringthe great war the British Government decided, in its wisdom, to establish a flying field in Scotland, at which aviators were to be trained in dropping bombs. The commission having this matter in hand chose a site on the shores of Loch Doon. In laying out the field a bog had to be drained; then a railway was constructed, hangars were erected, and other operations were carried out, entailing altogether an expenditure of half a million pounds. At a certain late stage in the proceedings the disconcerting discovery was made that the field could never be successfully used for the purpose intended, on account of the gusts and eddies produced by the surrounding hills. The undertaking was therefore abandoned. The authorities had presumably enlisted the skill of engineers from the outset of the work—but they had failed to consult a meteorologist!
A few such object lessons seem to be necessary to demonstrate the fact—which ought to be obvious—that meteorology is an indispensable and vital adjunct of aeronautics. This fact is now pretty well understood. Nearly all the activities of mankind are more or less influenced by weather, but few, if any, to such an extent as aeronautical enterprises. Hence a definite branch of applied science—Aeronautical Meteorology—is rapidly taking shape. Alreadyit enters into the curriculum of aeronauts; it has profoundly modified the methods of the ordinary meteorological services of the world; and it is raising a crop of specialists, some of whom are now employed by the business firms that manufacture or operate aircraft.
The statement has constantly been made since the war that aeronauts are becoming “independent” of the weather. This statement has a grain of truth in it, but no more. It is a fact that, under war conditions, aviators flew in every sort of weather, and often with impunity. Even since the war commercial aircraft have negotiated adverse atmospheric conditions with remarkable success. A spectacular feat of this sort was achieved on August 28, 1919, when a passenger-carrying aeroplane on the Paris-London route, piloted by Lieutenant Shaw, flew over this route through a hurricane blowing in gusts of from 40 to over 100 miles an hour, accompanied by a torrential rainstorm and such poor visibility that the pilot was frequently obliged to fly very low in order to pick up his landmarks and make sure that he was on his course. The flight was accomplished in 1 hour and 50 minutes—about half an hour less than schedule time. It is said that “the two passengers in the cabin of the machine emerged without any appearance at all of strain”—such as they certainly would have experienced if they had made the crossing by the Channel steamer on that boisterous day. In fact the land and sea route was seriously disorganized by the storm, and the Continental trains were arriving in London hours late.
Lest hasty conclusions should be drawn from this episode it should be stated at once that the company operating the air route in question, far from consideringitself independent of weather, is not content with the detailed bulletins furnished to aeronauts by the British Meteorological Office (which specializes in aeronautical meteorology more extensively than any other official weather service in the world), but maintains an elaborate weather service of its own, with an able meteorologist at the head of it.
An accurate statement of the situation would be that wind and weather are no longer the grave dangers that they once were to the aeronaut; but they are still, and will probably always be, factors of the utmost importance in the successful and profitable operation of aircraft. In order to make this matter plain it will be necessary for us, first of all, to devote a few words to some of the fundamental principles involved in aerial navigation.
The layman who sees nothing mysterious in the ascent of a balloon is, in general, somewhat puzzled by the phenomenon of a heavier-than-air machine rising from the ground. Yet, in both cases, the ascent of the vehicle depends upon the fact that air is not just empty space, but a material substance, possessing density, weight, and other properties many of which pertain also to solids. A balloon rises not because it is light, but because the air about it is heavy. In other words, gravity pushes the air under the balloon more forcibly than it pulls the balloon downward. The ability of an aeroplane to leave the ground depends upon the fact that air offers resistance to bodies moving through it.
THE EFFECT OF AIR RESISTANCE ON AN AEROPLANE
THE EFFECT OF AIR RESISTANCE ON AN AEROPLANE
Suppose a vertical plane (A)—such, for example, as the wind shield of an automobile—is moving horizontally through still air. The resistance of the air impedes its motion, and a part of the motivepower is employed in overcoming this resistance. Now, suppose the plane (B) is nearly, but not quite, horizontal, and is propelled by a force tending to make it move in the direction indicated by the arrow. This is approximately the case of an aeroplane driven by a motor; the plane representing the wings of the machine. Only a part of the air’s resistance is now effective in impeding the forward motion of the plane. The rest of it pushes the plane upward. If you hold your hand at such an angle and move it through water you will feel an analogous upward push. Moreover, you will notice that the faster you move your hand the greater is the push. Not only does this upward pressure of a fluid upon an inclined plane moving through it vary with the speed of the latter (to be exact, as the square of the speed), but it also varies with theangle which the plane presents to the fluid in its path. If the wing of an aeroplane, for example, cuts the air nearly edgewise, the upward pressure will be slight. As it departs from an edgewise position, (with the front edge higher than the rear), the upward pressure increases, but not indefinitely; beyond a certain rather small angle it begins to diminish.
In an aeroplane the upward pressure, or “lift,” is increased by giving the wings a slightly arched shape, or “camber.” The air flows over the arched wings in such a way as to produce a suction above them which helps the push from below. The actual amount of lift for a given speed has been determined by experiments for wings of various shapes and sizes and set at various angles to the line of motion. If, when the machine is in the air, the lift is just sufficient to counterbalance the weight of the aeroplane, the latter flies horizontally. An increase in lift causes the machine to rise; a decrease in lift permits gravity to pull it down.
Now suppose the aviator is flying horizontally and wishes to climb. At the rear of the machine and forming part of its tail is a hinged horizontal flap called the “elevator,” under the control of the pilot. By giving this flap an upward tilt he causes the air to exert a downward pressure on the tail of the machine, and hence the nose of the machine is carried upward. While the inertia of the aeroplane tends to carry it along the original path, its wings now present a greater angle to the air, the lift is increased, and the machine rises. The reverse of this operation will cause the machine to descend.
The Bed of Potomac River, at Washington.From an altitude of a few hundred or a few thousand feet, submarine features are clearly revealed to great depths. Objects have thus been photographed 45 feet under water. The shoals are submerged to a depth of from 2 to 5 feet. In favorable weather, aerial photographs are valuable in making hydrographic surveys. (Photographed from the air by Dr. W. T. Lee, U. S. Geological Survey.)
The Bed of Potomac River, at Washington.From an altitude of a few hundred or a few thousand feet, submarine features are clearly revealed to great depths. Objects have thus been photographed 45 feet under water. The shoals are submerged to a depth of from 2 to 5 feet. In favorable weather, aerial photographs are valuable in making hydrographic surveys. (Photographed from the air by Dr. W. T. Lee, U. S. Geological Survey.)
A vertically hinged flap in the tail, acting on exactly the same principle as the rudder of a ship,enables the pilot to turn horizontally. Two or more small horizontal flaps, known as “ailerons,” attached to the wings, are used to preserve the lateral balance of the machine, and to give it the proper “bank,” or inclination, when making a turn.
Drilling with Compressed Air in a Copper Mine.The drill also forces a stream of water into the hole to lay the dangerous sulphur-bearing dust. (Courtesy Sullivan Machinery Co.)
Drilling with Compressed Air in a Copper Mine.The drill also forces a stream of water into the hole to lay the dangerous sulphur-bearing dust. (Courtesy Sullivan Machinery Co.)
Launching a Weather Bureau Kite from the “Seneca” During the International Ice Patrol, to Explore the Air Over the Ocean.(Photograph, U. S. Weather Bureau.)
Launching a Weather Bureau Kite from the “Seneca” During the International Ice Patrol, to Explore the Air Over the Ocean.(Photograph, U. S. Weather Bureau.)
Launching a Weather Bureau Kite from the “Seneca” During the International Ice Patrol, to Explore the Air Over the Ocean.
(Photograph, U. S. Weather Bureau.)
With these few details in mind, we shall be prepared to consider, in a general way, how the behavior of an aeroplane is affected by the wind and other atmospheric phenomena.
With respect to wind there is an important difference between aircraft and marine craft. Mere strength of wind is not dangerous to an aeroplane, except when starting or landing. An aviator flying above the clouds, with no landmarks in sight by which to gauge his movements, is no more conscious of the actual wind at that level, provided it is steady, than he is of the rotation of the earth on its axis. He feels the wind produced by the motion of his machine through the air—the so-called “relative wind”—but no other. The true wind may be a mere zephyr, or a hurricane blowing 150 miles an hour; the effect is the same on his machine, so far as he is able to observe. On the other hand, a strong wind has a very different effect from a light one upon the course of the aeroplane’s flight with respect to the ground beneath. If a pilot, with no landmarks to guide him, steers by compass for a certain point, and if there is a strong cross-wind of which he is unaware, he will be carried far out of his course; a wind dead ahead or astern will merely affect the speed of his flight, so that he will arrive later or sooner at his destination than he expected.
One of the important problems of aeronautics, especially from the commercial point of view, is toprevent aircraft from being driven off their course by the wind when flying with no visible landmarks; i. e., over clouds, fog, the ocean, or an unmapped country. When this problem is solved, pilots will fly above the clouds much more commonly than they do now. The winds at high levels are generally both steadier and stronger than at low. The stronger wind is an advantage or a disadvantage, according to whether it is blowing in the direction of flight or the reverse; but as the winds at different levels generally blow in different directions, a pilot who is independent of landmarks can choose whatever level affords the winds most favorable for his intended journey.
Over established air routes quite elaborate measures are now adopted to keep pilots informed of the direction and speed of the wind at different levels, so that they can make due allowance for this factor in shaping their course. In clear weather this information is easily obtained by sighting the drift of a pilot balloon with a theodolite, or by observing in a specially designed graduated mirror or pair of mirrors the drift of the smoke cloud from a shell fired by an anti-aircraft gun and timed to burst at any desired altitude. In cloudy weather the smoke trails can often be successfully observed through small breaks in the clouds. When the sky is completely overcast, a succession of shells is fired at definite short intervals of time and the distances apart of the puffs of smoke and the direction of the line in which they lie are determined from an aeroplane flying above the spot. Another method, which was devised by the French military meteorological service during the war, is to send up small balloons loaded with bombs which burst after a certain time,the position of each burst being determined by sound-ranging from the ground.
These methods of providing information concerning the winds at flying levels have, however, their serious limitations, and aeronauts now look hopefully to the perfection of the existing systems of “directional wireless,” whereby the pilot will receive whenever desired, or at regular intervals, a wireless signal from the terminus of his route or some other known point, the direction from which the signal comes being indicated by suitable apparatus on the aeroplane. Thus aided, he should never deviate far from his course, unless he chooses to.
For long journeys, such as the crossing of the Atlantic, the air pilot will naturally make use of all available information concerning the great permanent or semipermanent wind systems of the earth, such as the trade winds of the lower atmosphere, the antitrades above them, and the fairly constant eastward drift of the atmosphere at high levels in middle latitudes. The dividend-earning capacity of commercial aircraft necessarily depends upon taking advantage of favorable winds, while adverse winds may mean not only a loss of money but the danger of prolonging a journey until the fuel supply is exhausted—a serious predicament over the ocean and also over lands remote from civilization. It is, however, a common error on the part of current writers to overrate the constancy and reliability of the winds in various parts of the world, and to lay too much stress on the value of permanent wind charts. What the aeronaut needs especially to know is the typical behavior of the winds with respect to the distribution of barometric pressure, as shown by a weather map,including their variations with altitude. The time will come when the information necessary for plotting the winds at various levels will be flashed at frequent intervals by high-powered radio stations to aerial navigators in all parts of the world—a system that is already in its initial stages, especially in Europe. A pilot making a long journey will thus be able to lay his course so as to utilize the winds that will speed him on his way. Even violent storms, such as the mariner seeks to avoid, will be turned to advantage by the airman.
We have now to consider another aspect of wind that is of much more interest to the airman than to the seaman, and that is the question of “wind structure.” The layman usually thinks of a wind as a nearly steady horizontal flow of air. Such winds exist, but they are exceptional, especially in the lower levels of the atmosphere. A wind is generally full of gusts and eddies, upcurrents and downcurrents, and it is these eccentricities that gradually develop in the aviator a sort of sixth sense—a “feel” for atmospheric fluctuations, that enables him to adjust his machine instinctively to the forces tending to disturb its equilibrium. He also learns by experience the conditions under which irregularities of a pronounced character may be expected. He becomes well acquainted with the great mound of air that drives his machine upward when passing over a hill or mountain; with the eddy that lurks in the lee of such an obstacle; with the downward tendency of the air over lakes, rivers, swamps and forests.
“The air is so sensitive,” writes the late well-known British flyer, Gustav Hamel, “that it is affected even by the color of large patches of vegetation.Whether this be entirely due to the different heat-radiating power of different colors it is impossible to say, but invariably an aeroplane on passing from grass land to a field covered with yellow flowers experiences a certain amount of air disturbances only less noticeable than the inevitable bump experienced in passing from green fields to ploughed land, or from ploughed land to meadow.”
When the wind is blowing, the air for at least a few hundred feet above the ground is nearly always in a state of turmoil. This is partly due to the friction of the moving fluid against the irregular surface of the earth, and partly to the ascending and descending currents caused by differences in temperature. The latter effect is illustrated in the rapid rise of air over a bare sunlit plain and its fall over an adjacent forest or body of water. Ascending currents are often made visible by the formation of detached cumulus clouds, each of which marks the summit of a rising column of moist air, while in the spaces between the clouds the air is generally sinking. Measurements with balloons have shown that vertical currents often attain speeds of 600 feet a minute or more, while the process of hail formation appears to indicate that in thunderstorm clouds there are violent uprushes amounting to 2,000 or 2,500 feet a minute, and possibly much more. The descending air current between clouds is sometimes so strong that an aeroplane cannot force its way up through it.
THE FLOW OF AIR OVER TWO RIDGES(After Dr. Franz Linke.)Notice the eddy in the valley to the leeward of the first ridge
THE FLOW OF AIR OVER TWO RIDGES(After Dr. Franz Linke.)Notice the eddy in the valley to the leeward of the first ridge
THE FLOW OF AIR OVER TWO RIDGES
(After Dr. Franz Linke.)
Notice the eddy in the valley to the leeward of the first ridge
A SHELTERED LANDING PLACE MAY BE DANGEROUS(After Dr. Franz Linke.)A landing place surrounded by trees is dangerous in windy weather on account of the air waves formed between the moving air above and the calm air below.
A SHELTERED LANDING PLACE MAY BE DANGEROUS(After Dr. Franz Linke.)A landing place surrounded by trees is dangerous in windy weather on account of the air waves formed between the moving air above and the calm air below.
A SHELTERED LANDING PLACE MAY BE DANGEROUS
(After Dr. Franz Linke.)
A landing place surrounded by trees is dangerous in windy weather on account of the air waves formed between the moving air above and the calm air below.
AIR WAVES NEAR THE EARTH’S SURFACEThe waves are made visible by smoke
AIR WAVES NEAR THE EARTH’S SURFACEThe waves are made visible by smoke
AIR WAVES NEAR THE EARTH’S SURFACE
The waves are made visible by smoke
The turbulence of the lower air—a phenomenon that adds so much to the difficulties of starting and landing—extends to various heights, depending especially upon the strength of the wind. A rough rule, evolved by the Zeppelin pilots before the war,was to expect turbulent conditions up to an altitude equal to from ten to twenty times the force of the wind in meters per second. Thus, for a wind of 10 meters per second, the turbulent layer would be from 100 to 200 meters thick. A good picture of the atmospheric ups and downs encountered by the airmanwhen flying low is furnished by the behavior of the smoke from a factory chimney with a moderate wind blowing, forming smoke waves.
THE WIND’S AUTOGRAPH ON A GUSTY DAY, RECORDED WITH A PRESSURE-TUBE ANEMOMETERThe vertical lines are hour lines and the horizontal lines show the force of the wind in miles an hour and also in pounds a square foot.
THE WIND’S AUTOGRAPH ON A GUSTY DAY, RECORDED WITH A PRESSURE-TUBE ANEMOMETERThe vertical lines are hour lines and the horizontal lines show the force of the wind in miles an hour and also in pounds a square foot.
THE WIND’S AUTOGRAPH ON A GUSTY DAY, RECORDED WITH A PRESSURE-TUBE ANEMOMETER
The vertical lines are hour lines and the horizontal lines show the force of the wind in miles an hour and also in pounds a square foot.
These disturbances give rise to the very marked fluctuations in the force of the wind known as gusts. There are certain forms of anemometer especially designed to record the gustiness of the wind. A record of the wind’s force is traced by a pen on a moving strip of paper, and the “anemogram” thus obtained shows a continuous series of irregularities, the extent of which increases with the strength of the wind. The puffs and lulls often alternate at intervals of a few seconds or less, and the actual force of the wind at a given instant may be many times greater than its average force for, say, five minutes. An ordinary anemometer does not indicate these rapid fluctuations, but merely shows the time required for a mile of wind to flow past the instrument. Thus when such an instrument tells us that the wind is blowing at the rate of 40 miles an hour,it may actually be varying between 20 and 60 miles an hour, or between even wider limits.
Since the matter became of practical importance on account of the needs of aviation, many interesting studies have been made of the effects of different kinds of topography upon the overlying air currents. A striking example of the eccentric winds that sometimes prevail in mountain valleys has been described by Mr. B. M. Varney, of the University of California, in the “Monthly Weather Review.” From the summit of a steep cliff about 1,100 feet above the floor of Yosemite Valley the writer launched broad sheets of tissue paper, and, with the aid of powerful binoculars, followed their flight as they were carried in huge spirals, thousands of feet in diameter, finally disappearing beyond the mountains on the opposite side of the valley. The accompanying sketch shows the path of one of these papers. From its starting point atAuntil it passed behind the summit of Liberty Cap (B), more than a mile distant, the paper was watched for 7 minutes. The top of Liberty Cap is some 1,600 feet above the point at which the flight began. This sketch visualizes one of the ticklish problems that will some day confront the pilot of a sight-seeing or mail-carrying aeroplane in the Yosemite National Park.
AIR CURRENTS IN YOSEMITE VALLEY(Sketched by B. M. Varney.)The flight of a sheet of paper across the valley.
AIR CURRENTS IN YOSEMITE VALLEY(Sketched by B. M. Varney.)The flight of a sheet of paper across the valley.
AIR CURRENTS IN YOSEMITE VALLEY
(Sketched by B. M. Varney.)
The flight of a sheet of paper across the valley.
Although, on an average, the air is much steadier at high levels than near the ground, very unsteady currents are sometimes found at all altitudes attainable by aircraft. Thunderclouds, thousands of feet above the earth, are always the seat of violent turmoil, but such clouds can, as a rule, be avoided by the airman. When a stratum of air glides over another differing sharply from it in density—and distinct strata of this sort are not uncommon inthe atmosphere—friction between the strata sets up waves like those produced in water by wind blowing over it. If the two streams are moving in the same direction, but at different speeds, the waves are long and regular; when they are more or less crossed, the waves are short and choppy. The moisture at the crests of these waves may be cooled to such an extent as to condense into visible clouds, arranged in long continuous rolls or rows of detached patches; forms frequently assumed by cirro-cumulus and alto-cumulus. More often, however, the waves of air remain invisible, because the conditions of moisture and temperature are not right for the production of cloud.
Recalling, now, what has been said above about the way in which the lift of an aeroplane varies with the angle at which the wings meet the air and also with the speed of the machine relative to the air, it will be easy to understand some of the difficulties experienced in maintaining one’s equilibrium when flying in a turbulent atmosphere. Waves, eddies, vertical currents and other features of wind structure cause abrupt changes in the attitude and the speed of the machine with respect to the air stream. The sudden increases and decreases of lift thus produced have much the same effect upon the machine as if it were running over a solid obstacle on the one hand or plunging into a vacuous space in the atmosphere on the other, and hence are aptly described by aviators as “bumps” and “holes in the air,” respectively. The latter term, which seems to have become firmly rooted in all languages (French,trou d’air; German,Luftloch; etc.), has had the unfortunate effect of keeping alive in the public mind the idea that the aviator occasionally runs into avacuum or semivacuum, such as could not exist in the atmosphere. (The nearest approach to such a thing is the rarefaction in the core of a tornado or waterspout, due to the enormous centrifugal force of the vortex; something that no aviator has yet encountered.)
To make matters worse, different parts of the sustaining surface of the machine may receive different impulses. One wing, for example, may graze a violent uprush of air not encountered by the other, giving the aeroplane a tilt to one side, or the tail of the machine may be driven in one direction and the nose in the other. Again, the whole machine may suddenly enter an air current of quite different speed and direction from the one in which it has been flying. To take an extreme case, it may run into a stream of air flowing just as fast, and in the same direction, as the machine itself, with the result that therelativewind becomes zero, and the machine, deprived of all lift, drops like a stone until it acquires a velocity with respect to its new environment.
When such conditions prevail, the pilot is kept busy with his “controls”; now moving his elevator to adjust his fore-and-aft balance, and now his ailerons to set him on an even keel laterally, and occasionally turning his rudder to offset the effects of horizontal gusts. The elevator and the ailerons are worked with a single lever, colloquially called the “joy-stick,” and the rudder with a bar which the pilot operates with his feet. Ordinary adjustments of this kind are performed automatically by the trained aviator, but violent disturbances call for the exercise of skill and judgment. Generally speaking, no amount of atmospheric turbulence causes anyserious trouble to the trained pilot, except when he is flying close to the ground, as in starting and landing.
Before we leave the subject of wind it will be well to emphasize once more the fact, which the average layman has difficulty in grasping, that the only movements of the air that affect the safety and comfort of flight are the movements relative to the machine, and not those relative to the ground. To the aviator, when he is once clear of the ground, a steady wind of any speed is merely a mass of calm air. Hence an aviator will sometimes have perfectly smooth flying when the wind, as measured on the earth, is blowing 40 or 50 miles an hour; and again he will describe the air as rough and bumpy when flags are hanging limp from their staffs and dwellers onterra firmadeclare that not a breath of air is stirring. In the early days of flying aviators themselves were afraid of a strong wind. Thus Wilbur Wright, during his pioneer exhibition flights in France, would never go up unless the smoke from his cigarette rose in a straight line, and until about the end of 1909 no aviator attempted to fly in a wind of 20 miles an hour.
At the present time the only atmospheric condition that seriously hampers flying is fog or low cloud. An aviator flying in a fog or cloud is not only liable to wander far from his course, on account of the unknown leeway of his machine, but he is often in great doubt as to his proximity to the ground. One of the curious effects of such a situation is that the airman loses his sense of the vertical. On land our sense of up and down is determined by the force of gravity, pulling us toward the earth. When riding in a terrestrial vehicle, weare conscious of other pushes and pulls; such, for example, as the jolt that pitches us forward when a train stops suddenly, or the outward thrust that we feel when swinging around a curve. Again, in descending in a lift we seem to lose weight, as if gravity had suddenly grown weaker. On earth all such impressions are corrected by the sight of objects around us; but the aviator enveloped in mist has no such guides, and he often becomes quite confused about the direction of the ground. A turn, which involves banking, increases his confusion. Eventually he may be flying almost upside down without being aware of the fact. Professor Melville Jones, who has been through such experiences, says of the pilot’s confusion:
“His first indication that something is wrong is, as a rule, either an increase or a decrease of speed that is not counteracted by the accustomed movements of the controls. A period of wild suspense and utter bewilderment now follows, during which the pilot makes violent efforts to recover control, but without success. The next thing that he realizes, if he realizes anything at all, is that he is either on his back or spinning, and the next thing he knows is that he is out of the clouds with the earth standing up at a ridiculous angle and spinning round like a drunken dinner plate. Happy is he that has plenty of air room under these circumstances.”
Spirit-levels and similar instruments are affected by the same disturbances that mislead the pilot in his estimation of the vertical; but fortunately there are certain other devices, due to the exigencies of the war, during which cloud flying was a part of the tactics of the military aviator, which have virtuallysolved this problem, though their use has not yet become general.
The outstanding difficulty of a fog is the problem of landing. In the case of a forced landing, at a distance from a regular landing-ground, the pilot must simply trust to luck. He may descend in the water or the treetops, or on rough ground that will wreck his machine, but he has no choice. The only solution of this difficulty is the installation of a reserve engine, or some other expedient that will obviate the necessity of forced landings. The task of finding a landing ground in a fog and descending to it in safety will, in the near future, be comparatively simple. Most fogs, though by no means all, are so shallow that it is possible to tether a kite-balloon so that it will float above the fog and indicate the position of the aerial harbor. Several such balloons, flying tandem, would afford sufficient lift to support a series of electric lanterns along the cable, for use at night. Searchlights and “star shells” have been employed for the same purpose. Directional wireless and the wireless telephone seem likely, however, to be the chief dependence of the future aeronaut seeking port in a fog. These devices will also be the means of averting collisions in a fog or cloud along crowded airways, and especially in the congestion that will prevail in the vicinity of important air ports. Last but not least, the artificial dispersion of fog by means of electrical discharges, although still in the experimental stage, holds out possibilities of being the ultimate solution of the fog problem, not only for the aeronaut, but also for the mariner, the railway manager, and everybody else who is incommoded by a misty atmosphere.
Even when he is not flying in clouds or fog the aviator by no means always enjoys a clear view of distant objects. A slight haze impairs visibility, while a heavy rainstorm or snowstorm may obstruct the aeronaut’s view as badly as a fog.
Of the meteorological elements that affect aeronautics, other than those we have mentioned, the most important is the density of the atmosphere—generally expressed in terms of barometric pressure. The air diminishes in density upward, and the rarefied atmosphere of high levels has several effects on aircraft. Its decreased buoyancy imposes a limit upon the ascent of balloons; its decreased resistance makes it necessary for an aeroplane to fly at greater speed in order to get the same lift; it diminishes the power of gasoline engines, on account of the reduced supply of air; and it has various unpleasant and even dangerous effects on the aeronaut, similar to “mountain sickness.” The level that a given aeroplane cannot exceed owing to the combined effect of reduced lift and reduced engine power is known as its “ceiling.” Different types of aeroplane have very different ceilings.
At great altitudes the air is always very cold, summer and winter. The low temperature may interfere with the efficient working of the engine, and it is, of course, a source of discomfort to the pilot. The formation of ice and heavy deposits of snow lead to inconveniences in both aeroplanes and airships. The pelting of hail is sometimes a painful experience for aeronauts. Lastly, lightning has hitherto left aviators unscathed, but has caused numerous disasters among balloonists.
The recent rapid development of aeronautics has laid a heavy burden of additional labor upon the meteorologicalservices of the world, and is producing something like a revolution in their methods. The history of these changes is interesting. From the beginning of the twentieth century until a few years before the World War meteorologists were engaged in a great campaign of upper-air research, utilizing kites, captive balloons, pilot balloons, and sounding balloons to measure the winds, temperature, humidity and pressure at various levels in the atmosphere. In other words, aeronautical methods were employed in the service of meteorology, but the investigators hardly entertained the idea of reversing the relation and making meteorology the handmaiden of aeronautics. The point of view prevailing in those days is well indicated by the fact that the organization that had charge of the upper-air explorations throughout the world was known as the “International Commission for Scientific Aeronautics,” a name that it bore until the year 1919.
The plan for providing regular weather reports for the benefit of aeronauts began with some small-scale enterprises in Germany about 1909. In the summer of that year Dr. Franz Linke organized a storm-warning service in connection with the International Aeronautical Exposition at Frankfort, and at the beginning of the year 1911 an aeronautical weather bureau for the whole of Germany was established, with headquarters at the Observatory of Lindenberg. Shortly before the war a similar undertaking was launched in Italy, under Dr. Matteucci, whose service was the first one in the world to publish daily charts, based on telegraphic reports, of the winds at various levels over an entire country.
During the war the regular meteorological services of the belligerent countries and the meteorologicalunits attached to the armies and navies maintained an almost continuous service of weather information for the great fleets of fighting aircraft. Bulletins, distributed chiefly by wireless telegraphy, supplied particulars of the current and prospective winds at the flying levels, the prevalence of fog, the degree of visibility, etc. New telegraphic weather codes, far more elaborate than those in use before the war, were devised for transmitting such information, and the whole business of observing and reporting weather became immensely more arduous than it had been in the days when the only interests served by practical meteorology were those of the land and the water.
Since the close of hostilities great efforts have been made to maintain these new operations of the meteorological establishments at something like the level attained during the war. The task is, however, beset with difficulties, on account of the great expense involved. It is being accomplished with different degrees of success in different countries.
Oneof the most astonishing paradoxes connected with the misapplication of human brains and energy glorified with the name of the “art of war” is this—that, while weather has always played an important part, and often a decisive one, in military operations, no attempt was ever made until a few years ago to include meteorology in the purview of military science or to utilize the services of meteorologists at the battle front.
The most casual survey of the history of warfare reveals the fact that atmospheric conditions rank high among the “controls” of fighting. From a military point of view, weather and climate bear a certain analogy to topography. They are a part of the physical environment with which a commander has to reckon. Weather, however, differs from topography in the fact that it is subject to rapid changes, and is therefore doubly worthy of attention on the part of an army, which must not only take account of the weather as observed and in progress, but must also, as far as possible, anticipate that which is to follow.
Everybody will recall the ruin that overtook the French army in Russia in 1812 on account of untoward weather conditions, but it is less well known that Napoleon, with his usual sagacity, obtained from his scientific advisers areport on the Russian climate before he planned his campaign; that the winter set in much earlier than usual in that fatal year; and, most interesting of all, that it was actually a brief period of thawing weather, rather than the intense cold that preceded and followed it, which, by turning the roads into bogs and breaking up the ice in the Beresina, brought about the culminating disaster.
Another fateful spell of weather ushered in the battle of Waterloo. It is described in a well-known passage of “Les Misérables,” which contains enough truth mingled with hyperbole to be worth quoting:
“S’il n’avait pas plu dans la nuit du 17 au 18 janvier, 1815, l’avenir de l’Europe était changé. Quelques gouttes de plus ou de moins out fait pencher Napoléon. Pour que Waterloo fût la fin d’Austerlitz, la Providence n’a eu besoin que d’un peu de pluie, et un nuage traversant le ciel à contre-sens de la saison a suffi pour l’écroulement d’un monde.”
The rains and floods that led to the annihilation of the Roman legions under Varus inA. D.9 and the great tempests that helped English seamen defeat the Spanish Armada furnish additional well-known examples of the immense importance of weather as a factor in warfare. We need not, however, look farther back than to the recent world conflict to find similar examples in profusion. Leaving out of consideration the indirect effects of the weather upon the progress of the war as exercised through its control of crops, transportation, and other features in the economic life of the belligerent and neutral nations, we need only examine war-time newspapers to see how the armies themselves were helped or harassed by meteorological conditions at every turn. The war was a great popular teacher of climatography,just as it was of geography. The drenching misery of Flemish winters, as formidable to the soldiers in the trenches as the bullets of the enemy, became as familiar to the present generation of Americans as did somewhat similar conditions in Virginia to Americans of the Civil War period.
The British campaigns in Mesopotamia were as much a conflict with climate as with human foes. Marches were made when the temperature stood at 110 degrees Fahrenheit and over. The temperature in the hospital tents is said to have reached 130 degrees. The disaster at Kut-el-Amara was due to the rains and floods that prevented reenforcements from reaching the beleaguered garrison. The failure of the Dardanelles expedition was partly due to the fact that the extreme dryness of the country was not realized—as it would have been if the War Office had called climatologists into council—and totally inadequate provision was made for the water supply.
The new engines of war brought forth by the recent struggle were peculiarly susceptible to the effects of weather. The larger guns and heavy motor trucks were difficult to move over muddy roads. The aircraft, though they managed to fly in all kinds of weather, suffered innumerable disasters for which atmospheric conditions—chiefly storms and fog—were responsible, and their operations were conspicuously affected by favorable and unfavorable winds. Shells were fired to unprecedented heights, and their trajectories were modified by unknown conditions in the upper air. Last but not least, the use of poisonous gases, especially in the period before gas clouds were largely replaced by gas shells, was dependent upon the occurrence of appropriate winds; and a slight miscalculation in thisrespect sometimes brought disaster to the troops using the gas.
It is not surprising that professional meteorologists played a part in the World War, but it is difficult to understand why meteorological units were not attached to all armies, at least when on active service, several decades before the year 1914. Meteorologists did, indeed, take a hand in one earlier conflict, but not as enrolled soldiers. During the Spanish-American War a special service was organized by the United States Weather Bureau to protect the American fleet in southern waters from unpleasant surprises in the shape of West India hurricanes. In the summer of 1898 a chain of observation stations was established by the Bureau around the Caribbean Sea. The service then inaugurated in consequence of the exigencies of war proved so valuable to shipping in time of peace that it has continued to operate, with some intermissions, down to the present day.
When the World War broke out, the only country that immediately put meteorologists, as such, into the field was Germany. The Germans were fortunate in having a far greater number of trained meteorologists at their disposal than had their enemies. There were chairs of meteorology in several German universities and high schools, and the numerous meteorological observatories and institutes of the Empire had provided occupation for a large amount of professional talent in this line. One of the first acts of the army that invaded Belgium was to establish an aerological service in that country.
The Entente countries were slow in adding meteorological units to their armies, but their civilian meteorological services were utilized to the utmostfor military purposes from the beginning of the war. They at first worked under difficulties arising from the cessation of the customary weather reports from central Europe, but, to offset this disadvantage, the weather map was expanded in other directions, the number of daily hours of observation was increased, and eventually the forecasters in London and Paris acquired much better facilities for making their predictions than they had enjoyed in time of peace. The supply of weather information to the public was suspended, and great precautions were taken to prevent the reports of the Allied services from being utilized by the enemy. The German meteorologists were seriously hampered by the lack of reports from the westward. It has been asserted that such reports were sometimes obtained by radio from submarines stationed off the coast of Ireland, but such a service, if it existed, must have been fragmentary and unsatisfactory. That the Germans made many mistakes in their attempts to infer the atmospheric conditions over the British Isles from the limited weather map at their disposal is proved by the fact that their airships frequently crossed the Channel when, with an ampler knowledge of impending weather, they would certainly have remained at home. Several Zeppelins came to grief in the course of these ill-timed raids. One of the interesting routine duties of the British Meteorological Office during the war was to draw the weather map for a given moment as the Germans would probably draw it, with their curtailed set of telegraphic reports, and then predict the German prediction!
In the spring of 1915 a small meteorological section was organised in the British Army, and attached to the Royal Engineers. This force wasafterward enlarged, and provided units for service on several battle fronts. The British also developed a naval meteorological service, which had existed in embryo before the war, and, eventually, a special meteorological service for the Royal Air Force. Analogous services were organized by the French and the Italians.
The United States Army and the United States Navy both established meteorological services not long after this country entered the war. The former was attached to the Signal Corps, and was partly officered and recruited from the Weather Bureau. A training school for army meteorologists was opened at College Station, Texas. Upward of 300 men were given instruction in this school, and most of them were sent overseas. The naval meteorological service was headed by the director of Blue Hill Observatory, and the junior officers received special training at that institution.
The varied activities carried on by these war-time units were so different from the traditional duties of meteorologists that they may be said to mark the advent of a new branch of applied science—Military Meteorology. They were, moreover, as we shall see, extremely fruitful of effects upon the science of meteorology in general.
In the principal battle zones the military weather men maintained a dense network of observation stations, the reports from which, combined with those received from the regular peace-time weather stations of the Allied and neutral countries, enabled the forecasters at headquarters to keep closely in touch with atmospheric changes. Observations of both surface and upper-air conditions were made at frequent intervals, and radiotelegraphy was largelyused to insure prompt transmission of the reports. In general, weather maps were drawn four times a day. Information was distributed locally to the fighting units by telephone and otherwise.
The vast fleet of aircraft called into being by the war would, of itself, have imposed upon the military meteorologists the necessity of paying a great amount of attention to the upper air. Pilot balloons were sent up so frequently and at so many points that the aviators generally knew just what winds they would encounter aloft. Special arrangements were made to follow the progress across the country of the thundersqualls which constituted a serious danger to the “sausages,” or observation balloons, as well as to aeroplanes on the ground, and to hangars.
There was, however, another urgent reason for keeping a close watch of the winds and other atmospheric conditions at various levels above the earth’s surface. Experience acquired early in the war proved that old-fashioned methods of correcting the aim of artillery for meteorological disturbances were extremely inadequate for modern guns, the projectiles of which rise to altitudes of from 10,000 to 20,000 feet and encounter conditions quite different from those prevailing at the surface. The flight of a projectile is affected by the force and direction of the wind, and the density of the air through which it passes. Some modern projectiles remain in the air as long as 70 seconds, and a moderate wind blowing across the path of such a projectile may easily cause it to fall half a mile away from the point at which it would strike if fired in still air. One of the routine duties of the army weather service was to observe the winds and computethe air-densities at different heights wherever such information was required by the artillery. In order to facilitate the application of such data by the gunners ingenious methods were developed for computing what is known as the “ballistic wind.” This is a fictitious wind which, if affecting the projectile throughout its flight, would produce the same total deflective effect and effect on range as the various winds that the projectile actually encounters.
Meteorological observations were also of great importance in connection with the new process of locating distant guns known as “sound-ranging.” This process consists, briefly, in determining the exact instant of arrival at several points of the sound waves propagated through the air from the gun that is being located. If sound traveled at a uniform speed, these observations would show the exact distance of each of the observing points from the gun, and a simple geometrical construction would indicate the position of the latter. The speed of sound waves in the air is, however, affected by both wind and temperature. Accordingly, allowance had to be made for these varying factors, and the necessary data were supplied by the meteorological units.
The observation and prediction of winds favoring the use of poisonous gases by friend or foe was one of the most delicate tasks allotted to the army meteorologists. The flow of such gases is determined by the winds close to the surface of the earth, and these are greatly affected by topography. Local air currents controlled by the slope of the ground were especially utilized for gas attacks. Strong winds were unfavorable, because they quickly dissipated the gas cloud. The meteorologists not onlyadvised their own troops when to use gas, but also gave warning when the atmospheric conditions were such that gas was likely to be used by the enemy. The use of gas shells was less dependent for its success upon the wind than the liberation of gas clouds, but even when shells were used the wind and weather at the objective point were factors of importance.
The exigencies of warfare developed several new features of meteorological practice, the utility of which did not cease with the war. Thus it became customary to measure the degree of “visibility” of distant objects, for the benefit of aviators and gunners, and this element was included in the routine weather reports. Scales of visibility, ranging from “very bad” to “excellent,” etc., were adopted, and eventually certain forms of apparatus (“visibility meters”) were devised for getting fairly precise measurements of this weather factor.
Another novel practice that deserves to be perpetuated was the plan adopted by the military forecasters of adding to their predictions a statement as to their probable accuracy; this was expressed on a numerical scale of “odds,” instead of by use of the vague terms “probably” and “possibly,” which have generally served the purpose of the dubious forecaster.
The war brought about many improvements in the instruments and methods used in sounding the upper air; and the intensive campaign of pilot-balloon observations carried out at the military stations provided a body of data for study quite unparalleled in the history of meteorology.
Lastly, the war revolutionized weather telegraphy in Europe. Before the war the European forecasterswere hampered by exasperating delays in the collection of reports over the telegraph lines, especially in the international exchange of observations. Wireless telegraphy had been extensively used for gathering reports from vessels and supplying vessels with forecasts, but not for the interchange of meteorological information on land. The war changed all this. Radiotelegraphic weather messages became the rule, and the advantages of the new system were so obvious that the tendency has been to retain it as far as possible since the war.