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our postage-cards, and four such answers were conveyed for one franc.*
The Parisians will long recollect the excitement produced by the arrival of their pretty couriers; no sooner was a pigeon seen in the air than the whole city was aroused, and remained in a state of intense anxiety till the news was delivered. An engraving was afterwards published representing Paris, as a woman in mourning, anxiously awaiting, like Noah's imprisoned family, the return of the dove.
The aerial post was undoubtedly a great success. not indeed save France, or deliver the Capital; but it was an immense comfort and advantage to the Parisians as establishing, during the whole of the siege, a correspondence with the exterior, which without it would have been impossible. And had the cause been less desperate, it is not improbable that the balloons might have turned the scale, by giving to the French substantial advantages in their means of communication.
We must now, in conclusion, say a few words on the general capabilities and prospects of the balloon as a means of aerial locomotion. The problem is one of great interest and importance; for it need hardly be said that if such a mode of transit could be established, its advantages would be almost incalculable. The balloon already fulfils, as we have seen, one of the two necessary conditions; it will float in the air, and it can be made to rise and fall at pleasure.† But it fails in the second particular. The
* The following official notice, of a kind unique in postal annals, may still be seen on the walls of some of the French provincial towns :
'DIRECTION GÉNÉRALE DES TÉLÉGRAPHES ET DES POSTES.Avis.-Les derniers ballons ont apporté de Paris, avec la correspondance de la capitale, des cartes destinées à recevoir des réponses à des questions posées dans la lettre d'envoi. La direction assurera la transmission de ces réponses au moyen des pigeonsvoyageurs, désireuse d'ajouter ainsi aux moyens de correspondance qu'elle a déjà mis à la disposition du public pour ses relations avec la capitale, un nouveau mode de communications, moins complet, il est vrai, mais moins onéreux. Les cartesréponses seront reçues dans tous les bureaux de télégraphe et de poste moyen-nant une taxe uniforme d'un franc. Elles ne pourront contenir que quatre réponses, par oui ou par non, consignées dans des colonnes disposées à cet effet.. Les bureaux de poste sont également autorisés à recevoir des sommes d'argent à destination de Paris et de l'enceinte fortifiée jusqu'à concurrence de 300 fr., et à délivrer en échange des mandats qui, transmis à Paris par des pigeons-voyageurs, y seront acquittes à présentation.. La direction prend des mesures pour donner aux opérations photographiques nécessaires pour la réproduction et la réduction des telégrammes et des mandats un développement en rapport avec les nouvelles facilités qu'elle est heureuse de pouvoir accorder au public.-STEENACKERS. Tours.' (No date, but it must have been early in October, 1870.)
†The present mode of doing this, involving a continual loss of gas and ballast, and a consequent waste of ascending power, is very imperfect: it was one of Mr. Green's objects, in the invention of the guide-rope, to ameliorate the evil, by pro
The great obstacle at present to its use is the want of power over the direction of its flight. It is at the mercy of the wind, which 'bloweth where it listeth ;' and a vehicle which can only travel to some unknown place is not likely to have many business passengers.
It has often been proposed to take advantage of the fact, well ascertained by experience, that currents are found, at different heights, moving in different directions; but the information on this point is at present very imperfect; and probably such a mode of direction would be always uncertain. The more important problem is, how to make a balloon travel, not with, but through the air; in the same manner as a boat, instead of being floated along with the stream, is made to move in an independent course through the water. In short, we want what, if we may coin a word for the purpose, we may call a dirigible balloon.
The Montgolfiers, in 1783, discussed the use of oars, and Guyton de Morveau, in the following year, made some experiments at Dijon with analogous contrivances. But no useful result was obtained, and the question does not appear to have been studied, with any earnest attention to its mechanical conditions, until the middle of the present century.
The nature of these conditions may best be learnt by considering the analogous case of a boat; not a sailing boat which is moved by external power, but a rowing boat or a steamer in which the power is internal. In such a vessel the motion is produced by oars, paddles, or screws, the surfaces of which are impelled against the circumambient fluid by mechanical power; the reaction sends the vessel forward, and when the motion through the fluid is once obtained, the direction is determined by that simple and beautiful contrivance, the rudder.
According to this, in order to make our balloon move through the air, it must be provided with propelling apparatus, propelling power, and a rudder. And, as a further condition, derived from aquatic analogy, it must have such a form as will offer the least resistance in its passage through the air. If these conditions are complied with, we shall certainly get a dirigible balloon, and they involve nothing that is at variance with mechanical knowledge, or that is beyond the scope of mechanical skill.
The first good attempt to make such a balloon was in 1852 by a French engineer, M. Henri Giffard. He was then young
viding a kind of ballast which could be discharged temporarily, and taken in again; and no doubt this expedient, combined with a perfectly impermeable envelope, would much extend the limit of balloon voyages. There is, however, great room for improvement in this particular. K 2
and unknown, but his name has since become famous on other grounds. He had evidently studied the subject well, and had arrived at a thoroughly practical appreciation of the necessary conditions. Abandoning the globular shape, as offering too much resistance, and following the analogy of the lines of a vessel, he constructed an oblong pointed balloon, to the stern of which he attached a rudder, and in the car he carried a small steam-engine, which worked a screw, formed of sails like a windmill. The following sketch (taken from M. Louis Figuier's 'Merveilles de la Science') will give an idea of M. Giffard's
balloon. It was about 150 feet long, and 40 feet diameter. It contained 88,000 cubic feet, and was filled with coal-gas. The engine was three-horse power, weighing 3 cwt., and it turned the screw 110 revolutions per minute. It was a daring thing to put the furnace of a steam-engine so near to a huge reser
voir of highly inflammable gas; but M. Giffard adopted, among other precautions, the ingenious device of turning the chimney downwards, producing the draught by the steam-blast, as in the locomotive-engine; and he considered himself free from any danger of fire.
The ascent took place from the Hippodrome in Paris on the 24th September, the signal to 'let go' being given by the steamwhistle. The wind was strong, and M. Giffard did not expect to hold against it; he found, however, that he could make a headway through the air of five to seven miles an hour; and this enabled him to execute various manoeuvres of circular
motion with perfect success. The action of the rudder was very sensitive. No sooner, he says, did he pull gently one of the cords, than he saw the horizon turn round him like the moving picture in a panorama. He rose to a height of nearly 6000 feet, but, the night approaching, he put out his fire, and descended safely in a field near Elancourt.*
In 1855 M. Giffard constructed another balloon, of larger dimensions, which confirmed the previous results; but he found that before the direction could be completely commanded, many improvements were necessary which would take time. His attention was just then occupied on other mechanical inven
* M. Emile de Girardin, in noticing (La Presse,' 25 Sept. 1852) this experiment of M. Giffard, whom he calls the Fulton of aerial navigation, makes the following remarks:
Est-il pour la France une solution plus importante que celle du problème de la navigation aérienne? La navigation maritime à vapeur a changé toutes les conditions relatives d'existence insulaire et européenne de la Grande Bretagne; ce que l'Angleterre pouvait entreprendre il y a cinquante ans contre la France elle ne pourrait plus l'essayer sans s'exposer aux terribles représailles d'un débarquement qui pourrait faire craindre à la ville de Londres le sort de la ville de Copenhague.
'La navigation à vapeur peut également changer toutes les conditions relatives de puissance continentale et militaire de la Russie. En effet, on comprend que toutes les combinaisons de la guerre seront changées le jour où, au lieu de lancer certains projectiles, il n'y aura plus qu'à les laisser tomber au milieu d'un carré d'infanterie.
'Ce n'est là qu'un des points par lesquels la navigation aérienne à vapeur s'élève à la hauteur d'une immense question politique.'
The following letter on the same subject was written at a later date to Gaston Tissandier.
'Hauteville House, 9 mars 1869.
'Je crois, Monsieur, à tous les progrès. La navigation aérienne est consécutive à la navigation océanique; de l'eau l'homme doit passer à l'air. Partout où la création lui sera respirable, l'homme pénétrera dans la création. Notre seule limite est la vie. Là où cesse la colonne d'air dont la pression empêche notre machine d'éclater, l'homme doit s'arrêter. Mais il peut, doit, et veut aller jusque-là et il ira. Certes, l'avenir est à la navigation aérienne, et le devoir du présent est de travailler à l'avenir.
'Voyages Aériens.'-(French edition only.)
tions,* but he did not neglect the subject, for, in the great captive balloons erected by him in 1867 and 1868, he perfected several of the improvements he had in contemplation, in particular the impermeability of the envelope, a more mechanical construction of the valves, and a better and cheaper mode of preparing pure hydrogen.
During the siege of Paris, the earnest desire to get a returnpost to the city again called attention to the subject of dirigible balloons. In October 1870, M. Dupuy de Lôme, the eminent Naval Architect to the French Government, obtained a grant of sixteen hundred pounds for experiments, and he proceeded to construct an apparatus, which was in progress when the Communist insurrection broke out and stopped the proceedings. On peace being restored, M. de Lôme resumed the work at his own cost, and the trial was made on the 2nd of February, 1872. He has given a full account of his proceedings in several papers of the Comptes-rendus 't of the Academy of Sciences. His balloon was elongated, 120 feet long, and 50 feet diameter, containing 122,000 cubic feet, and it was filled with hydrogen. It had a triangular rudder, and the car carried a screw-propeller of two sails, 30 feet diameter, intended to be turned by four men, a relay-gang being also taken up to relieve them. M. de Lôme considered it essential that the balloon should preserve its form in spite of any escape of gas, and, to ensure this, he placed, inside the large envelope, a smaller balloon, which could be filled with air from the car when required.
The ascent took place at Vincennes, with M. de Lôme and thirteen other persons in the car. In the early exposition of his objects he had stated that he did not aim at attaining any great independent speed; the important point was to get such a moderate control over the course as should render it possible for balloons to return into Paris, and he believed that a motion through the air of about five miles (eight kilometres) per hour would suffice for this purpose. Soon after leaving the ground the screw was put in motion, and, on the rudder being taken in hand, its influence was at once observable. The wind was high, blowing from the south-west, with a velocity varying from 27 to 37 miles an hour, and all that could be hoped for was to produce a moderate deviation in the direction of the flight. This was accomplished, as, when the screw was put to work, and the head of the balloon set at right angles to the wind, a deviation was
* M. Giffard has acquired great fame by his invention of the Injector,' an apparatus now applied almost universally to locomotives, and which is one of the most remarkable and novel applications of science to engineering.
+ Vol. lxxi. 1870, p. 502; and vol. lxxiv. 1872, p. 337.