the dominion of the air-第39节
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t smaller； measuring only 91 feet by 30 feet； and operated by an electric motor placed in circuit with a powerful battery of bichromate cells。 Two trials were made with this vessel in October； 1883； and again in the following September； when it proved itself capable of holding its course in calm air and of being readily controlled by the rudder。
But； ere this； a number of somewhat similar experiments； on behalf of the French Government； had been entered upon by Captains Renard and Krebs at Chalais…Meudon。 Their balloon may be described as fish…shaped； 165 feet long； and 27。5 feet in principal diameter。 It was operated by an electric motor； which was capable of driving a screw of large dimensions at forty…eight revolutions per minute。 At its first trial； in August； 1884； in dead calm； it attained a velocity of over twelve miles per hour； travelling some two and a half miles in a forward direction； when； by application of the rudder and judicious management； it was manoeuvred homewards； and practically brought to earth at the point of departure。
A more important trial was made on the 12th of the following month； and was witnessed by M。 Tissandier； according to whom the aerostat conveying the inventors ascended gently and steadily； drifting with an appreciable breeze until the screw was set in motion and the helm put down； when the vessel was brought round to the wind and held its own until the motor； by an accident； ceased working。 A little later the same air ship met with more signal success。 On one occasion； starting from ChalaisMeudon； it took a direct course to the N。E。； crossing the railway and the Seine； where the aeronauts； stopping the screw； ascertained the velocity of the wind to be approximately five miles an hour。 The screw being again put in motion； the balloon was steered to the right； and； following a path parallel to its first； returned to its point of departure。 Starting again the same afternoon； it was caused to perform a variety of aerial evolutions； and after thirty…five minutes returned once more to its starting place。
A tabular comparison of the four navigable balloons which we have now described has been given as follows：
Date。 Name。 Motor。 Vel。 p。 Sec。 1852 M。 Henri Giffard Steam engine 13。12 ft。 1872 M。 Dupuy de Lome Muscular force 9。18 ft。 1883 MM。 Tissandier Electric motor 9。84 ft。 1884 MM。 Renard & Krebs Electric motor 18。04 ft。
About this period； that is in 1883； and really prior to the Meudon experiments； there were other attempts at aerial locomotion not to be altogether passed over； which were made also in France； but financed by English money。 The experiments were performed by Mr。 F。 A。 Gower； who； writing to Professor Tyndall； claims to have succeeded in 〃driving a large balloon fairly against the wind by steam power。〃 A melancholy interest will always belong to these trials from the fact that Mr。 Gower was subsequently blown out to sea with his balloon； leaving no trace behind。
At this stage it will be well to glance at some of the more important theories which were being mooted as to the possibility of aerial locomotion properly so called。 Broadly； there were two rival schools at this time。 We will call them the 〃lighter…than…air…ites〃 and the 〃heavier…than…air…ites；〃 respectively。 The former were the advocates of the air vessel of which the balloon is a type。 The latter school maintained that； as birds are heavier than air； so the air locomotive of the future would be a machine itself heavier than air； but capable of being navigated by a motor yet to be discovered； which would develop proportionate power。 Sir H。 Maxim's words may be aptly quoted here。 〃In all Nature；〃 he says； 〃we do not find a single balloon。 All Nature's flying machines are heavier than the air； and depend altogether upon the development of dynamic energy。〃
The faculty of soaring； possessed by many birds； of which the albatross may be considered a type； led to numerous speculations as to what would constitute the ideal principle of the air motor。 Sir G。 Cayley； as far back as 1809； wrote a classical article on this subject； without； however； adding much to its elucidation。 Others after his time conceived that the bird； by sheer habit and practice； could perform； as it were； a trick in balancing by making use of the complex air streams varying in speed and direction that were supposed to intermingle above。
Mr。 R。 A。 Proctor discusses the matter with his usual clear…sightedness。 He premises that the bird may； in actual fact； only poise itself for some ten minutesan interval which many will consider far too smallwithout flap of the wings； and； while contending that the problem must be simply a mechanical one； is ready to admit that 〃the sustaining power of the air on bodies of a particular form travelling swiftly through it may be much greater or very different in character from what is supposed。〃 In his opinion； it is a fact that a flat body travelling swiftly and horizontally will sink towards the ground much more slowly than a similar body moving similarly but with less speed。 In proof of this he gives the homely illustration of a flat stone caused to make 〃 ducks and drakes。〃 Thus he contends that the bird accomplishes its floating feat simply by occasional powerful propulsive efforts； combined with perfect balance。 From which he deduces the corollary that 〃if ever the art of flying； or rather of making flying machines； is attained by man； it will be by combining rapid motion with the power of perfect balancing。〃
It will now appear as a natural and certain consequence that a feature to be introduced by experimentalists into flying machines should be the 〃Aeroplane；〃 or； in other words； a plane which； at a desired angle； should be driven at speed through the air。 Most notable attempts with this expedient were now shortly made by Hiram Maxim； Langley； and others。
But； contemporaneously with these attempts； certain feats with the rival aerostatthe balloonwere accomplished； which will be most fittingly told in this place。
CHAPTER XX。 A CHAPTER OF ACCIDENTS。
It will have been gathered from what has been already stated that the balloonist is commonly in much uncertainty as to his precise course when he is above the clouds； or when unable from darkness to see the earth beneath him。 With a view of overcoming this disadvantage some original experiments were suggested by a distinguished officer； who during the seventies had begun to interest himself in aeronautics。
This was Captain Burnaby。 His method was to employ two small silk parachutes； which； if required； might carry burning magnesium wires； and which were to be attached to each other by a length of silk thread。 On dropping one parachute； it would first partake of the motion of the balloon； but would presently drop below； when the second parachute would be dismissed； and then an imaginary line drawn between the two bodies was supposed to betray the balloon's course。 It should be mentioned； however； that if a careful study is made of the course of many descending parachutes it will be found that their behaviour is too uncertain to be relied upon for such a purpose as the above。 They will often float behind the balloon's wake； but sometimes again will be found in front； and sometimes striking off in some side direction； so wayward and complex are the currents which control such small bodies。 Mr。 Glaisher has stated that a balloon's course above the clouds may be detected by observing the grapnel； supposed to be hanging below the car； as this would be seen to be out of the vertical as the balloon drifted； and thus serve to indicate the course。 However this may be； the most experienced sky sailors will be found to be in perplexity as to their direction； as also their speed； when view of the earth is obscured。
But Captain Burnaby is associated notably with the adventurous side of ballooning； the most famous of his aerial exploits being； perhaps； that of crossing the English Channel alone from Dover on March 23rd； 1882。 Outwardly； he made presence of sailing to Paris by sky to dine there that evening； inwardly； he had determined to start simply with a wind which bid fair for a cross…Channel trip； and to take whatever chances it might bring him。
Thus； at 10。30 a。m。； just as the mail packet left the pier； he cast off with a lifting power which rapidly carried him to a height of 2；000 feet； when he found his course to be towards Folkestone。 But by shortly after 11 o'clock he had decided that he was changing his direction； and when； as he judged； some seven miles from Boulogne； the wind was carrying him not across； but down the Channel。 Then； for nearly four hours； the balloon shifted about with no improvement in the outlook； after which the wind fell calm； and the balloon remained motionless at 2；000 feet above the sea。 This state of things continuing for an hour； the Captain resolved on the heroic expedient of casting out all his ballast and philosophically abiding the issue。 The manoeuvre turned out a happy one； for the balloon； shooting up to 11；000 feet； caught a current； on which it was rapidly carried towards and over the main land； and； when twelve miles
