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national code flag signal of distress, a square flag having either above it or below it a ball ; a continuous sounding with any sound appa- ratus; or a succession of white Very's lights. The following signals are used to require an aircraft to land : by day, three discharges, at intervals of 10 seconds, of a projectile showing on bursting black or yellow smoke; by night, a similar projectile showing on bursting red stars or lights. In fog and bad visibility, sound signals may be used.

From the date of the formation of the British Royal Flying Corps in May 1912 the importance of wireless telegraphy in connexion with aircraft was fully recognized, both in the naval and military wings; and at a very early period of the World War its superiority over other methods of signalling from the air was clearly demonstrated. Standard patterns of instrument for naval and military work were gradually evolved ; how reliable even these early types were may be seen from the fact that a few of them are actually still in use to-day in a practically identical form. The demand for the control of artillery fire by aircraft became steadily greater until, at the Armis- tice, on the British section of the western front alone there were over 600 aeroplanes and approximately 1,000 ground stations in use. AH these machines were employing a spark system, and with the advent of the long-distance reconnaissance and bombing squadrons with their higher-powered sets the need became apparent for improvements allowing of less interference and, if possible, a larger number of machines working within the same limits of wave length-.

The introduction in the early part of 1917 of the oscillation- valve continuous-wave transmitter an extremely light and efficient instrument with a range of 100 m. from air to ground overcame these difficulties and opened up a new vista with immense possibilities. Reception of ground-station signals by aircraft, although actually accomplished by the military wing at Farnborough as far back as 1913, became a reliably consistent proposition. Air- craft, whose duties carried them over considerable distances, were enabled to maintain a constant communication with their base, and, what was perhaps more important, the introduction of the con- tinuous-wave set opened up the possibilities of the design of an efficient pattern of wireless telephone capable of withstanding the most rigorous usage.

Although hostilities terminated before the full benefits of these latter developments had become appreciable, the progress which has since resulted, both in service and civil aviation, is considerable. Airways have rapidly sprung into being, and the necessity for rapid signalling along the route, reporting arrivals, departures and delays of machines and of communicating with the aircraft them- selves, has been responsible for the growth in England of the seven ground stations now existing, and, abroad, of the stations of the continental airports. The Air convention provides that every air- craft used in public transport and capable of carrying ten or more persons shall be equipped with sending and receiving wireless apparatus, and to-day most of the passenger-carrying aeroplanes of the London-Paris and other continental routes are equipped for the transmission and reception of wireless telephony, and are thus enabled to keep in touch with the ground throughout their flight. On several occasions during the year 1921 telephone conversation was carried out direct between a passenger flying between London and the Continent and a friend in his own home or office in London; the line telephone being used as far as the aerodrome station at Croydon, and thence being relayed by wireless telephone to the aircraft.

Another important war development, now becoming more and more extensively used, which was the outcome of the determination of the direction of passage of electro-magnetic waves, is the system of navigation by " direction finding," or " radiogoniometry." By this system two or more ground stations can detect the position of ah aircraft using wireless telegraphy or telephony, and can pass that information direct to it within a few seconds.

The converse an aircraft taking the bearing by W/T of two or more W/T stations on the ground can plot her own position, and thus enable the navigator to settle his position without asking for any information from the ground stations. This method is still in its infancy, but will undoubtedly prove of value to aerial navigation.

(iii) Weather Information. The value of the collection and distribution of meteorological information for the assistance of aeronautics was early recognized, notably in Germany. In England in 1909 the Meteorological Office was represented on the Advisory Committee for Aeronautics; in 1010 a meteoro- logical station was started at the Royal Aircraft Factory, and in 1912 at the Central Flying School at Upavon; both of these eventually prepared daily weather charts, and were the pre- cursors of the present local distributive stations. During the war meteorological services developed under the War Office and the Admiralty, a portion of the service under the Admiralty being transferred in 1918 to the Air Ministry. In 1919-20 all branches of the Meteorological Service were coordinated and attached to the Air Ministry.

The information required for air traffic to-day consists of existing weather conditions on any route, or landing-ground forecasts and

warnings. General information as to weather conditions is provided by the Daily Weather Service of the Meteorological Office, which receives information by wireless telegraph or telephone four times daily from a network of observing-stations throughout the British Isles. The reports obtained from these are issued collectively in the form of synoptic messages four times daily, and are available to anyone within wireless range either in the British Isles or European countries, while the latter distribute^their local information in a similar manner. According to the code drawn up by the International Commission for Weather Telegraphy the information transmitted to the Central Office in these reports consists of surface conditions, atmospheric pressure, wind, general state of the weather, temperature, visibility, humidity, cloud, rainfall, upper-air conditions, etc., the observations relating to each element being very detailed. In addition to the above, reports and forecasts usually covering a period of 24 hours are issued four times daily to each of four Aviation Weather Groups into which the British Isles are divided. Warnings are issued from the Central Office to all flying-centres when gales are threatened.

Local distributive centres are fully equipped meteorological stations established at certain important flying-centres, especially terminals, and will eventually number about twenty. Their duties include local observation and the issue of special information to the Aviation Services within their area. The establishment of a regular air service such as that between London and Paris entails a distribu- tive station at each terminus, subsidiary observing-stations along the route, and the hourly distribution of information. While in the air the flier can obtain information as to the weather in front of him by wireless telephony or from ground signals. (V. B.-J.)

VIII. SEAPLANES

Early Attempts at Flying from the Water. Among the earliest aircraft designed to fly from, and alight on, the water were a French craft by M. Fabre (1910), the Parseval monoplane con- structed in Germany in 1911, and the Grabadini monoplane tested at Monaco in 1911. Their difficulties were considerable and their successes slight, but by the end of 1911 floats were sub- stituted for wheels on aeroplanes that were already proved to fly; thus in Oct. of that year Glenn Curtiss, in America, flew from the water on a craft adapted from the Curtiss aeroplane which won the Gordon Bennett Trophy at Reims two years before. Its performance as a hydro-aeroplane suffered from the extra weight and resistance of the floats. In England the first flight from the water was by Comm. Swarm, R.N., and S. V. Sippe on an Avro biplane with 35-H.P. Green engine at Barrowin Nov. 1911.

Henri Fabre's " Canard," an original "pusher " monoplane with a 5O-H.P. Gnome engine, made several straight flights at Monaco in April 1912, and Voisin, Caudron and R. E. Pelterie thereafter successfully equipped their standard aeroplanes with Fabre floats. This float was a fairshape, rectilinear in plan, and made of a wooden framework covered with proofed canvas. This type was displaced later by pontoon-shaped floats covered with 3-ply wood or mahogany planking.

In 1912 Colliex, on a Voisin " Canard " equipped as an " am- phibian " with both wheels and floats, left the land at Issy-les- Moulineaux, and alighted on the Seine at Auteuil. Donnet and Leveque in France in 1912 built and flew the first boat seaplane, a two-seater pusher having a central hull with the engine above the boat, sufficiently high under the plane for the airscrew to clear the hull. The tips of the lower plane carried small floats to balance the craft on the water, and wheels were later fitted to the hull. The high centre of thrust relative to its centre of gravity, which signalized this craft, had been demonstrated in 1909 by Bleriot on an aeroplane. The design of this boat generT ally made it the forerunner of the seaplane of 1921. In 1912 the Royal Aircraft Factory equipped an F.E. biplane pusher with floats, and later a tractor biplane was made there and flown from Frensham Lake to Southampton Water.

At the end of 1913, Short made a loo-H.P. Gnome tractor biplane waterborne on a single central float and small wing tip- floats. On the next seaplane, however, two floats were used in place of the central float. These craft and their successors proved fairly seaworthy, and were useful on naval manoeuvres. About this time the experience of the shocks met with, when flying from broken water, led to the use of rubber shock absorbers, be- tween the floats and the supporting struts.

In America, following the lead of Glenn Curtiss, several aeror planes were fitted with pontoons. Towards the end of 1912 Curtiss replaced the single central pontoon by a boat-shaped