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purpose he contrived a double balloon, which he expected would combine the advantages of both kinds a fire-balloon, 10.ft. in diameter, being placed underneath a gas-balloon of 37 ft. in diameter, so that by increasing or diminishing the fire in the former it might be possible to ascend or descend without waste of gas. Rozier was accompanied by P. A. Romain, and for rather less than half an hour after the aerostat ascended all seemed to be going on well, when suddenly the whole apparatus was seen in flames, and the unfortunate adventurers came to the ground from the supposed height of more than 3000 ft. Rozier was killed on the spot, and Romain only survived about ten minutes. A monument was erected on the place where they fell, which was near the sea-shore, about 4 m. from the starting-point.

The largest balloon on record (if the contemporary accounts are correct) ascended from Lyons on the 19th of January 1784. It was more than 100 ft. in diameter, about 130 ft. Early in height, and when distended had a capacity, it is large balloons. said, of over half a million cubic feet. It was called the "Flesselles" (from the name of its proprietor, we believe), and after having been inflated from a straw fire in seventeen minutes, it rose with seven persons in the car to the height of about 3000 ft., but descended again after the lapse of about a quarter of an hour from the time of starting, in consequence of a rent in the upper part.

Another large fire-balloon, 68 ft. in diameter, was constructed by the chevalier Paul Andreani of Milan, and on the 25th of February he ascended in it from Milan, remaining in the air for about twenty minutes. This is usually regarded as the first ascent in Italy (but see Monck Mason's Aeronautica, p. 247).

On the 7th of November 1836, at half-past one o'clock, a large balloon containing about 85,000 cub. ft. of gas ascended from Vauxhall Gardens, London, carrying Robert Hollond, M.P., Monck Mason and Charles Green, and descended about two leagues from Weilburg, in the duchy of Nassau, at half-past seven the next morning, having thus traversed a distance of about 500 m. in 18 hours; Liége was passed in the course of the night, and Coblentz in the early morning. In consequence of this journey the balloon became famous as the "Nassau Balloon" (fig. 6). Charles Green (1785-1870), who constructed It and subsequently became its owner, was the most celebrated of English aeronauts, and made an extraordinary number of ascents. His first, made from the Green Park, London, on the 19th of July 1821 at the coronation of George IV., was distinguished for the fact that for the first time coal-gas was used instead of hydrogen for inflating the balloon. In 1828 he made an equestrian ascent from the Eagle Tavern, City Road, London, seated on his favourite pony. Such ascents have since been repeated; in 1852 Madame Poitevin made one from Cremorne Gardens, but was prevented from giving a second performance by police interference, the exhibition outraging public opinion. It was in descending from the " Nassau Balloon " in a parachute that Robert Cocking was killed in 1837 (see PARACHUTE). Green was the inventor of the guide-rope, which consists of a long rope trailing below the car. Its function is to reduce the waste of gas and ballast required to keep the balloon at a proper altitude. When a balloon sinks so low that a good deal of the guide-rope rests on the ground, it is relieved of so much weight and therefore tends to rise; if on the other hand it rises so that most of the rope is lifted off the ground, it has to bear a greater weight and tends to sink.

In 1863 A. Nadar, a Paris photographer, constructed "Le Géant," which was the largest gas-balloon made up to that time and contained over 200,000 cub. ft. of gas. Underneath it was placed a smaller balloon, called a compensator, the object of which was to prevent loss of gas during the voyage. The car had two stories, and was, in fact, a model of a cottage in wicker-work, 8 ft. in height by 13 ft. in length, containing a small printing-office, a photographic department, a refreshmentroom, a lavatory, &c. The first ascent took place at five o'clock on Sunday the 4th of October 1863, from the Champ de Mars. There were thirteen persons in the car, including one lady, the

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princess de la Tour d'Auvergne, and the two aeronauts Louis and Jules Godard. In spite of the elaborate preparations that had been made and the stores of provisions that were taken up, the balloon descended at nine o'clock, at Meaux, the early descent being rendered necessary, it was said, by an accident to the valve-line. At a second ascent, made a fortnight later, there were nine passengers, including Madame Nadar. The balloon descended at the expiration of seventeen hours, near Nienburg in Hanover, a distance of about 400 m. A strong wind was blowing, and it was dragged over the ground for 7 or 8 m. All the passengers were bruised, and some seriously hurt. The balloon and car were then brought to England, and exhibited at the Crystal Palace at the end of 1863 and beginning of 1864. The two ascents of Nadar's balloon excited an extraordinary amount of enthusiasm and interest, vastly out of proportion to what they were entitled to. Nadar's idea was to obtain sufficient money, by the exhibition of his balloon, to carry out a plan Broyhl lo

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FIG. 6.-The Great Nassau Balloon.

of aerial locomotion he had conceived possible by means of the principle of the screw; in fact, he spoke of "Le Géant" as "the last balloon." He also started L'Aeronaute, a newspaper devoted to aerostation, and published a small book, which was translated into English under the title The Right to Fly.

Directly after Nadar's two ascents, Eugene Godard constructed a fire-balloon of nearly half a million cubic feet capacity-more than double that of Nadar's and only slightly less than that attributed to the "Flesselles" of 1783. The air was heated by an 18-ft. stove, weighing, with the chimney, 980 lb. This furnace was fed by straw; and the "car" consisted of a gallery surrounding it. Two ascents of this balloon, the first fire-balloon seen in London, were made from Cremorne Gardens in July 1864. After the first journey the balloon descended at Greenwich, and after the second at Walthamstow, where it was injured by being blown against a tree. Notwithstanding its enormous size, Godard asserted that it could be inflated in half an hour, and the inflation at Cremorne did not occupy more than an hour. In spite of the rapidity with which the inflation was effected, few who saw the ascent could fail to receive an impression unfavourable to the fire-balloon in the matter of safety, as a rough descent, with a heated furnace as it were in the car, could not be other than most dangerous.

Long balloon voyages.

In the summer of 1873 the proprietors of the New York Daily | tember 1804, Gay-Lussac ascended alone. The balloon left the Graphic, reviving a project discussed by Green in 1840, deter- Conservatoire des Arts at 9.40 A.M., and descended at 3.45 P.M. mined to construct a very large balloon, and enable between Rouen and Dieppe. The chief result obtained was the American aeronaut, John Wise, to realize his that the magnetic force, like gravitation, did not experience favourite scheme of crossing the Atlantic Ocean to any sensible variation at heights from the earth's surface which Europe, by taking advantage of the current from west we can attain to. Gay-Lussac also brought down air collected to east which was believed by many to exist constantly at heights at the height of nearly 23,000 ft., and on analysis it appeared above 10,000 ft. The project came to nothing owing to the that its composition was the same as that of air collected at the quality of the material of which the balloon was made. When it earth's surface. At the time of leaving the earth the thermometer was being inflated in September 1873 a rent was observed after stood at 82° F., and at the highest point reached (23,000 ft.) 325,000 cub. ft. of gas had been put in, and the whole rapidly it was 14.9° F. Gay-Lussac remarked that at his highest point collapsed. The size was said to be such as to contain 400,000 there were still clouds above him. cub. ft., so that it would lift a weight of 14,000 lb. No balloon voyage has yet been made of a length comparable to the breadth of the Atlantic. In fact only two voyages exceeding 1000 m. are on record that of John Wise from St Louis to Henderson, N.Y., 1120 m., in 1859, and that of Count Henry de la Vaulx from Paris to Korosticheff in Russia, 1193 m., in 1900. On the 11th of July 1897 Salomon Andrée, with two companions, Strendberg and Fränkel, ascended from Spitzbergen in a daring attempt to reach the North Pole, about 600 m. distant. One carrier pigeon, apparently liberated 48 hours after the start, was shot, and two floating buoys with messages were found, but nothing more was heard of the explorers.

At an early date the balloon was applied to scientific purposes. So far back as 1784, Dr Jeffries made an ascent from London in which he carried out barometric, thermometric and Scientific hygrometric observations, also collecting samples of ascents. the air at different heights. In 1803 the St Petersburg Academy of Sciences, entertaining the opinion that the experiments made on mountain-sides by J. A. Deluc, H. B. de Saussure, A. von Humboldt and others must give results different from those made in free air at the same heights, resolved to arrange a balloon ascent. Accordingly, on the 30th of January 1804, Sacharof, a member of the academy, ascended in a gasballoon, in company with a French aeronaut, É. G. Robertson, who at one time gave conjuring entertainments in Paris. The ascent was made at a quarter past seven, and the descent effected at a quarter to eleven. The height reached was less than 1 m. The experiments were not very systematically made, and the chief results were the filling and bringing down of several flasks of air collected at different elevations, and the supposed observation that the magnetic dip was altered. A telescope fixed in the bottom of the car and pointing vertically downwards enabled the travellers to ascertain exactly the spot over which they were floating at any moment. Sacharof found that, on shouting downwards through his speaking-trumpet, the echo from the earth was quite distinct, and at his height was audible after an interval of about ten seconds (Phil. Mag., 1805, 21, p. 193).

Some of the results reported by Robertson appearing doubtful, Laplace proposed to the members of the French Academy of Sciences that the funds placed by the government at their disposal for the prosecution of useful experiments should be utilized in sending up balloons to test their accuracy. The proposition was supported by J. A. C. Chaptal, the chemist, who was then minister of the interior, and accordingly the necessary arrangements were speedily effected, the charge of the experiments being given to L. J. Gay-Lussac and J. B. Biot. The principal object of this ascent was to determine whether the magnetic force experienced any appreciable diminution at heights above the earth's surface. On the 24th of August 1804, Gay-Lussac and Biot ascended from the Conservatoire des Arts at ten o'clock in the morning. Their magnetic experiments were incommoded by the rotation of the balloon, but they found that, up to the height of 13,000 ft., the time of vibration of a magnet was appreciably the same as on the earth's surface. They found also that the air became drier as they ascended. The height reached was about 13,000 ft., and the temperature declined from 63° to 51° F. The descent was effected about half-past one, at Meriville, 18 leagues from Paris.

In a second experiment, which was made on the 16th of Sep

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From 1804 to 1850 there is no record of any scientific ascents in balloons having been undertaken. In the latter year J. A. Bixio (1808-1865) and J. A. Barral (1819-1884) made two ascents of this kind. In the first they ascended from the Paris observatory on the 29th of June 1850, at 10.27 A.M., the balloon being inflated with hydrogen gas. The day was a rough one, and the ascent took place without any previous attempt having been made to test the ascensional force of the balloon. When liberated, it rose with great rapidity, and becoming fully inflated it pressed upon the network, bulging out at the top and bottom. The ropes by which the car was suspended being too short, the balloon soon covered the travellers like an immense hood. In endeavouring to secure the valve-rope, they made a rent in the balloon, and the gas escaped so close to their faces as almost to suffocate them. Finding that they were descending then too rapidly, they threw overboard everything available, including their coats and only excepting the instruments. The ground was reached at 10h. 45m., near Lagny. Of course no observations were made. Their second ascent was made on the 27th of July, and was remarkable on account of the extreme cold met with. At about 20,000 ft. the temperature was 15° F., the balloon being enveloped in cloud; but on emerging from the cloud, at 23,000 ft., the temperature sank to - 38° F., no less than 53° F. below that experienced by Gay-Lussac at the same elevation. The existence of these very cold clouds served to explain certain meteorological phenomena that were observed on the earth both the day before and the day after the ascent. Some pigeons were taken up in this, as in most other high ascents; when liberated, they showed a reluctance to leave the car, and then fell heavily downwards.

In July 1852 the committee of the Kew Observatory resolved to institute a series of balloon ascents, with the view of investigating such meteorological and physical phenomena as require the presence of an observer at a great height in the atmosphere. John Welsh (1824-1859) of the Kew Observatory was the observer, and the great "Nassau Balloon" was employed, with Green himself as the aeronaut. Four ascents were made in 1852, viz. on the 17th and 26th of August, the 31st of October and the 10th of November. The heights attained were 19,510, 19,100, 12,640 and 22,930 ft., and the lowest temperatures met with in the four ascents were 8.7° F. (19,380 ft.), 12.4° F. (18,370 ft.), 16-4° F. (12,640 ft.) and 10.5° F. (22,370 ft.). The decline of temperature was very regular. A siphon barometer, dry and wet bulb thermometers, aspirated and free, and a Regnault hygrometer were taken up. Some air collected at a considerable height was found on analysis not to differ appreciably in its composition from air collected near the ground. For the original observations see Phil. Trans., 1853, pp. 311-346. At the meeting of the British Association for the Advancement of Science held at Aberdeen in 1859, a committee was appointed for the purpose of making observations in the higher Glaisher's strata of the atmosphere by means of the balloon. ascents. For two years nothing was effected, owing to the want both of an observer and of a suitable balloon. After its reappointment at the Manchester meeting of 1861, the committee communicated with Henry Tracey Coxwell (1819-1900), an aeronaut who had made a good many ascents, and he agreed to construct a new balloon, of 90,000 cub. ft. capacity, on the condition that the committee would undertake to use it, and pay £25 for each high ascent made especially on its behalf, defraying

also the cost of gas, &c., so that the expense of each high ascent | magnet was taken in very many of the ascents, and the results amounted to nearly £50. An observer being still wanted, James of ten different sets of observations indicated that the time of Glaisher, a member of the committee, offered himself to take vibration was longer than on the earth. In almost all the the observations, and accordingly the first ascent was made on ascents the balloon was under the influence of currents of air in the 17th of July 1862, from the gas-works at Wolverhampton, different directions which varied greatly in thickness. The directhis town being chosen on account of its central position in the tion of the wind on the earth was sometimes that of the whole country. Altogether, Glaisher made twenty-eight ascents, the mass of air up to 20,000 ft., whilst at other times the direction last being on the 26th of May 1866. Of these only seven were changed within 500 ft. of the earth. Sometimes directly oppospecially high ascents, although six others were undertaken for site currents were met with at different heights in the same the objects of the committee alone. On the other occasions he ascent, and three or four streams of air were encountered moving availed himself of public ascents from the Crystal Palace and in different directions. The direct distances between the places other places of entertainment, merely taking his place like the of ascent and descent, apart from the movements of the balloon other passengers. In the last six ascents another aeronaut and under the influence of these various currents, were always very a smaller balloon were employed. The dates, places of ascent much greater than the horizontal movement of the air as measand greatest heights (in feet) attained in the twenty-eight ured by anemometers. For example, on the 12th of January ascents were-1862: July 17, Wolverhampton, 26,177; July 30, 1862, the balloon left Woolwich at 2h. 8m. P.M., and descended Crystal Palace, 6937; August 18, Wolverhampton, 23,377; at Lakenheath, 70 m. distant from the place of ascent, at 4h. August 20, Crystal Palace, 5900; August 21, Hendon, 14,355; 19m. P.M. At the Greenwich Observatory, by a Robinson September 1, Crystal Palace, 4190; September 5, Wolverhamp- anemometer, during this time the motion of the air was 6 m. ton, 37,000; September 8, Crystal Palace, 5428. 1863: March only. With regard to physiological observations, Glaisher found 31, Crystal Palace, 22,884; April 18, Crystal Palace, 24,163; that the frequency of his pulse increased with elevation, as June 26, Wolverton, 23,200; July 11, Crystal Palace, 6623; also did the number of inspirations. The number of his pulsaJuly 21, Crystal Palace, 3298; August 31, Newcastle-upon- tions was generally 76 per minute before starting, about 90 at Tyne, 8033; September 29, Wolverhampton, 16,590; October 9, 10,000 ft., 100 at 20,000 ft., and 110 at higher elevations. Crystal Palace, 7310. 1864: January 12, Woolwich, 11,897; But a good deal depended on the temperament of the individual. April 6, Woolwich, 11,075; June 13, Crystal Palace, 3543; This was also the case in respect to colour; at 10,000 ft. the June 20, Derby, 4280; June 27, Crystal Palace, 4898; August faces of some would be a glowing purple, whilst others would be 29, Crystal Palace, 14,581; December 1, Woolwich, 5431; scarcely affected; at 4 m. high Glaisher found the pulsations December 30, Woolwich, 3735. 1865: February 27, Woolwich, of his heart distinctly audible, and his breathing was very much 4865; October 2, Woolwich, 1949; December 2, Woolwich, affected, so that panting was produced by the slightest exertion; 4628. 1866: May 26, Windsor, 6325. at 29,000 ft. he became insensible. In reference to the propagation of sound, it was at all times found that sounds from the earth were more or less audible according to the amount of moisture in the air. When in clouds at 4 m. high, a railway train was heard; but when clouds were far below, no sound ever reached the ear at this elevation. The discharge of a gun was heard at 10,000 ft. The barking of a dog was heard at the height of 2 m., while the shouting of a multitude of people was not audible at heights exceeding 4000 ft. In his ascent of the 5th of September 1862, Glaisher considered that he reached a height of 37,000 ft. But that figure was based, 'not on actual record, but on the circumstances that at 29,000 ft., when he became insensible, the balloon was rising 1000 ft. a minute, and that when he recovered consciousness thirteen minutes later it was falling 2000 ft. a minute, and the accuracy of his conclusions has been questioned. Few scientific men have imitated Glaisher in making high ascents for meteorological observations. In 1867 and 1868 Camille Flammarion made eight or nine ascents from Paris for scientific purposes. The heights attained were not great, but the general result was to confirm the observations of Glaisher; for an account see Voyages aériens, Paris, 1870, or Travels in the Air, London, 1871, in which also some ascents by W. de Fonvielle are noticed. On the 15th of April 1875, H. T. Sivel, J. E. Crocé-Spinelli and Gaston Tissandier ascended from Paris in the balloon "Zenith," and reached a height of 27,950 ft.; but only Tissandier came down alive, his two companions being asphyxiated. This put an end to such attempts for a time. But Dr A. Berson and Lieut. Gross attained 25,840 ft. on the 11th of May 1894; Berson, ascending alone from Strassfurt on the 4th of December 1894, attained about 31,500 ft. and recorded a temperature of — 54° F.; and Berson and Stanley Spencer are stated by the latter to have attained 27,500 ft. on the 15th of September 1898 when they ascended in a hydrogen balloon from the Crystal Palace, the thermometer registering -29° F. On the 31st of July 1901, Berson and R. J. Süring, ascending at Berlin, actually noted a barometric reading corresponding to a height of 34,500 ft., and possibly rose 1000 or 1500 ft. higher, though in spite of oxygen inhalations they were unconscious during the highest portion of the ascent.

The primary object of the ascents was to determine the temperature of the air, and its hygrometrical state at different elevations to as great a height as could be reached; and the secondary objects were- (1) to determine the temperature of the dew-point by Daniell's and Regnault's hygrometers, as well as by the dry and wet bulb thermometers, and to compare the results; (2) to compare the readings of an aneroid barometer with those of a mercurial barometer up to the height of 5 m.; (3) to determine the electrical state of the air, (4) the oxygenic condition of the atmosphere, and (5) the time of yibration of a magnet; (6) to collect air at different elevations; (7) to note the height and kind of clouds, their density and thickness; (8) to determine the rate and direction of different currents in the atmosphere; and (9) to make observations on sound. The instruments used were mercurial and aneroid barometers, dry and wet bulb thermometers, Daniell's dew-point hygrometer, Regnault's condensing hygrometer, maximum and minimum thermometers, a magnet for horizontal vibration, hermetically sealed glass tubes exhausted of air, and an electrometer. In one or two of the ascents a camera was taken up.

The complete observations, both as made and after reduction, are printed in the British Association Reports, 1862-1866; here only a general account of the results can be given. It appeared that the rate of the decline of temperature with elevation near the earth was very different according as the sky was clear or cloudy; and the equality of temperature at sunset and increase with height after sunset were very remarkable facts which were not anticipated. Even at the height of 5 m., cirrus clouds were seen high in the air, apparently as far above as they seem when viewed from the earth. The results of the observations differed very much, and no doubt the atmospheric conditions depcnded not only on the time of day, but also on the season of the year, and were such that a vast number of ascents would be requisite to determine the true laws with anything approaching to certainty and completeness. It was also clear that England is a most unfit country for the pursuit of such investigations, as, from whatever place the balloon started, it was never safe to be more than an hour above the clouds for fear of reaching the sea. It appeared from the observations that an aneroid barometer could be trusted to read as accurately as a mercurial barometer to the heights reached. The time of vibration of a horizontal

The personal danger attending high ascents led Gustave Hermite and Besançon in November 1892 to inaugurate the

sending up of unmanned balloons (ballons sondes) equipped with automatic recording instruments, and kites (q.v.) have also been employed for similar meteorological purposes. (See also METEOROLOGY.)

The balloon had not been discovered very long before it received a military status, and soon after the beginning of the French revolutionary war an aeronautic school was Military founded at Meudon, in charge of Guyton de Morveau, balloons. the chemist, and Colonel J. M. J. Coutelle (1748-1835). | Four balloons were constructed for the armies of the north, of the Sambre and Meuse, of the Rhine and Moselle, and of Egypt. In June 1794 Coutelle ascended with the adjutant and general to reconnoitre the hostile army just before the battle of Fleurus, and two reconnaissances were made, each occupying four hours. It is generally stated that it was to the information so gained that the French victory was due. The balloon corps was in constant requisition during the campaign, but it does not appear that, with the exception of the reconnaissances just mentioned, any great advantages resulted, except in a moral point of view. But even this was of importance, as the enemy were much disconcerted at having their movements so completely. watched, while the French were correspondingly elated at the superior information it was believed they were gaining. An attempt was made to revive the use of balloons in the African campaign of 1830, but no opportunity occurred in which they could be employed. It is said that in 1849 a reconnoitring balloon was sent up from before Venice, as also were small balloons loaded with bombs to be exploded by time-fuses. In the French campaign against Italy in 1859 the French had recourse to the use of balloons, but this time there was not any aerostatic corps, and their management was entrusted to the brothers Godard. Several reconnaissances were made, and one of especial interest the day before the battle of Solferino. No information of much importance seems, however, to have been gained thereby.

In the American Civil War (1861) balloons were a good deal used by the Federals. There was a regular balloon staff attached to McClellan's army, with a captain, an assistant-captain and about 50 non-commissioned officers and privates. The apparatus consisted of two generators, drawn by four horses each; two balloons, drawn by four horses each, and an acid-cart, drawn by two horses. The two balloons used contained about 13,000 and 26,000 ft. of gas, and the inflation usually occupied about three hours. (See Royal Engineers' Papers, vol. xii.) By their aid useful information was gained about the enemy round Richmond and in other places, but eventually difficulties of transport and the topography of the theatre of war made ballooning impracticable; and little was heard of it after the first two years of the war.

The balloon proved itself very valuable during the siege of Paris (1870-71). It was by it alone that communication was kept up between the besieged city and the external world, as the balloons carried away from Paris the pigeons which afterwards brought back to it the news of the provinces. The total number of balloons that ascended from Paris during the siege, conveying persons and despatches, was sixty-four-the first having started on the 23rd of September 1870, and the last on the 28th of January 1871. Gambetta effected his escape from Paris, on the 7th of October, in the balloon "Armand-Barbés," an event which doubtless led to the prolongation of the war. Of the sixty-four balloons only two were never heard of; they were blown out to sea. One of the most remarkable voyages was that of the "Ville d'Orléans," which, leaving Paris at eleven o'clock on the 21st of November, descended fifteen hours afterwards near Christiania, having crossed the North Sea. Several of the balloons on their descent were taken by the Prussians, and a good many were fired at while in the air. The average size of the balloons was from 2000 to 2050 metres, or from 70,000 to 72,000 cub. ft. The above facts are extracted from Les Ballons du siège de Paris, a sheet published by Bulla and Sons, Paris, and compiled by the brothers Tissandier, wellknown French aeronauts, which gives the name, size and times of ascent and descent of every balloon that left Paris, with the

names of the aeronaut and generally also of the passengers, the weight of despatches, the number of pigeons, &c. Only those balloons, however, are noticed in which some person ascended. The balloons were manufactured and despatched (generally from the platforms of the Orleans or the Northern railway) under the direction of the Post Office. The aeronauts employed were mostly sailors, who did their work very well. No use whatever was made in the war of balloons for purposes of reconnaissance.

Ballooning, however, as a recognized military science, only dates back to about the year 1883 or 1884, when most of the powers organized regular balloon establishments. In 1884-85 the French found balloons very useful during their campaign in Tongking; and the British government also despatched balloons with the Bechuanaland expedition, and also with that to Suakin in those years. During the latter campaign several ascents were made in the presence of the enemy, on whom it was said that a great moral effect was produced. The employment of balloons has been common in nearly all modern wars.

The French in the campaigns of the 19th century used varnished silk We may briefly describe the apparatus used in military operations. balloons of about 10,000 cub. ft. capacity. The Americans in the Civil War used much larger ones, those of 26,000 cub. ft. being found the most suitable. These were also of varnished silk. In the present day most nations use balloons of about 20,000 cub. ft., made of varnished cambric; but the British war balloons, made of goldbeater skin, are usually of comparatively small size, the normal capacity being 10,000 cub. ft., though others of 7000 and 4500 cub. ft. have also been used, as at Suakin. The usual shape is spherical; but since 1896 the Germans, and now other nations, have adopted a long cylindrical-shaped balloon, so affixed to its cable as to present an inclined surface to the wind and thus act partly on the principle of a kite. Though coal-gas and even hot air may occasionally be used for inflation, hydrogen gas is on account of its lightness far preferable. In the early days of ballooning this had to be manufactured in the field, but nowadays it is almost universally carried compressed in steel tubes. About 100 such tubes, each weighing 75 lb, are required to fill a 10,000-ft. balloon. Tubes of greater capacity have also been tried.

The balloon is almost always used captive. If allowed to go free it will usually be rapidly carried away by the wind and the results of the observations cannot easily be transmitted back. Occasions may occur when such ascents will be of value, but the usual method is to send up a captive balloon to a height of somewhere about 1000 ft. With the standard British balloon two officers are sent up, one of whom has now particularly to attend to the management of the balloon, while the other makes the observations.

When

With regard to observations from captive balloons much depends on circumstances. In a thickly wooded country, such as that in which the balloons were used in the American Civil War, and in the war in Cuba (in which the balloon merely served to expose the troops to severe fire), no very valuable information is, as a rule, to be obtained; but in fairly open country all important movements of troops should be discernible by an experienced observer at any point The circumstances, within about four or five miles of the balloon. it may be mentioned, are such as would usually preclude one unaccustomed to ballooning from affording valuable reports. Not only is he liable to be disturbed by the novel and apparently hazardous situation, but troops and features of the ground often have so peculiar an appearance from that point of view, that a novice will troops or a ploughed field. Then again, much will depend on atmooften have a difficulty in deciding whether an object be a column of spheric conditions. Thus, in misty weather a balloon is well-nigh useless; and in strong winds, with a velocity of anything over 20 m. an hour, efficient observation becomes a matter of difficulty. some special point has to be reported on, such as whether there is any large body of troops behind a certain hill or wood, a rapid ascent may still be made in winds up to 30 m. an hour, but the balloon would then be so unsteady that no careful scouting could be made. It is usually estimated that a successful captive ascent can only be made in England on half the days of the year. As a general rule balloon ascents would be made for one of the following objects:to examine the country for an enemy; to reconnoitre the enemy's position; to ascertain the strength of his force, number of guns and exact situation of the various arms; also to note the plan of his earthworks or fortifications. During an action the aerial observer would be on the look-out for any movements of the enemy and give warning of flank attacks or surprises. Such an observer could also keep the general informed as to the progress of various detached parties of his own force, as to the advance of reinforcements, or to the conduct of any fighting going on at a distance. Balloon observations are also of especial aid to artillery in correcting their aim.

The vulnerability of a captive balloon to the enemy's fire has been tested by many experiments with variable results. One established

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