the dominion of the air-第44部分
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
experience know that it is an exceedingly difficult manoeuvre to keep a trail rope dragging on the ground if it is desirable to prevent contact with the earth on the one hand； or on the other to avoid loss of gas。 A slight increase of temperature or drying off of condensed moisture mayindeed； is sure to after a whilelift the rope off the ground； in which case the balloon； rising into upper levels； may be borne away on currents which may be of almost any direction； and of which the observer below may know nothing。 As to the actual divergence from the wind's direction which a trail rope and side sail might be hoped to effect； it may be confidently stated that； notwithstanding some wonderful accounts that have gone abroad； it must not be relied on as commonly amounting to much more than one or； at the most； two points。
Although it is to be feared that trustworthy information as to the ultimate destination of Andree's balloon may never be gained； yet we may safely state that his ever famous； though regrettable； voyage was the longest in duration ever attained。 At the end of 48 hours his vessel would seem to have been still well up and going strong。 The only other previous voyage that had in duration of travel approached this record was that made by M。 Mallet； in 1892； and maintained for 36 hours。 Next we may mention that of M。 Herve； in 1886； occupying 24 1/2 hours； which feat； however； was almost equal led by the great Leipzig balloon in 1897； which； with eight people in the car； remained up for 24 1/4 hours； and did not touch earth till 1；032 miles had been traversed。
The fabric of Andree's balloon may not be considered to have been the best for such an exceptional purpose。 Dismissing considerations of cost； goldbeaters' skin would doubtless have been more suitable。 The military balloons at Aldershot are made of this； and one such balloon has been known to remain inflated for three months with very little loss。 It is conceivable； therefore； that the chances of the voyagers； whose ultimate safety depended so largely upon the staying power of their aerial vessel； might have been considerably increased。
One other expedient； wholly impracticable； but often seriously discussed； may be briefly referred to； namely； the idea of taking up apparatus for pumping gas into metal receivers as the voyage proceeds； in order to raise or lower a balloon； and in this way to prolong its life。 Mr。 Wenham has investigated the point with his usual painstaking care； and reduced its absurdity to a simple calculation； which should serve to banish for good such a mere extravagant theory。
Suppose； he says； the gas were compressed to one…twentieth part of its bulk； which would mean a pressure within its receiver of 300 lbs。 per square inch； and that each receiver had a capacity of 1 cubic foot； while for safety sake it was made of steel plates one…twentieth of an inch thick； then each receiver would weigh 10 lbs。； and to liberate 1；000 feet clearly a weight of 500 lbs。 would have to be taken up。 Now； when it is considered that 1；000 cubic feet of hydrogen will only lift 72 lbs。； the scheme begins to look hope less enough。 But when the question of the pumping apparatus； to be worked by hand； is contemplated the difficulties introduced become yet more insuperable。 The only feasible suggestion with respect the use of compressed gas is that of taking on board charged cylinders under high pressure； which； after being discharged to supply the leakage of the balloon could； in an uninhabited country； be cast out as ballast last。 It will need no pointing out； however； that such an idea would be practically as futile as another which has gravely been recommended； namely； that of heating the gas of the balloon by a Davy lamp； so as to increase its buoyancy at will。 Major Baden…Powell has aptly described this as resembling 〃an attempt to warm a large hall with a small spirit lamp。'
In any future attempt to reach the Pole by balloon it is not unreasonable to suppose that wireless telegraphy will be put in practice to maintain communication with the base。 The writer's personal experience of the possibilities afforded by this mode of communication； yet in its infancy； will be given。
CHAPTER XXV。 THE MODERN AIRSHIPIN SEARCH OF THE LEONIDS。
In the autumn of 1898 the aeronautical world was interested to hear that a young Brazilian； M。 Santos Dumont； had completed a somewhat novel dirigible balloon； cylindrical in shape； with conical ends； 83 feet long by 12 feet in diameter； holding 6；500 cubic feet of gas； and having a small compensating balloon of 880 cubic feet capacity。 For a net was substituted a simple contrivance； consisting of two side pockets； running the length of the balloon； and containing battens of wood； to which were affixed the suspension cords； bands being also sewn over the upper part of the balloon connecting the two pockets。 The most important novelty； however； was the introduction of a small petroleum motor similar to those used for motor tricycles。
The inventor ascended in this balloon； inflated with pure hydrogen； from the Jardin d'Acclimatation； Paris； and circled several times round the large captive balloon in the Gardens； after which； moving towards the Bois de Boulogne； he made several sweeps of 100 yards radius。 Then the pump of the compensator caused the engine to stop； and the machine； partially collapsing； fell to the ground。 Santos Dumont was somewhat shaken； but announced his intention of making other trials。 In this bold and successful attempt there was clear indication of a fresh phase in the construction of the airship； consisting in the happy adoption of the modern type of petroleum motor。 Two other hying machines were heard of about this date； one by Professor Giampietre； of Pavia； cigar…shaped； driven by screws； and rigged with masts and sails。 The other； which had been constructed and tested in strict privacy； was the invention of a French engineer； M。 Ader； and was imagined to imitate the essential structure of a bird。 Two steam motors of 20…horse power supplied the power。 It was started by being run on the ground on small wheels attached to it； and it was claimed that before a breakdown occurred the machine had actually raised itself into the air。
Of Santos Dumont the world was presently to know more； and the same must be said of another inventor； Dr。 Barton； of Beckenham； who shortly completed an airship model carrying aeroplanes and operated by clockwork。 In an early experiment this model travelled four miles in twenty…three minutes。
But another airship； a true leviathan； had been growing into stately and graceful proportions on the shores of the Bodenzee in Wurtemberg； and was already on the eve of completion。 Count Zeppelin； a lieut。…general in the German Army； who had seen service in the Franco…German War； had for some years devoted his fortune and energy to the practical study of aerial navigation； and had prosecuted experiments on a large scale。 Eventually； having formed a company with a large capital； he was enabled to construct an airship which in size has been compared to a British man…of…war。 Cigar…shaped； its length was no less than 420 feet； and diameter 40 feet； while its weight amounted to no more than 7；250 lbs。 The framework； which for lightness had been made of aluminium； was； with the object of preventing all the gas collecting at one end of its elongated form； subdivided into seventeen compartments； each of these compartments containing a completely fitted gas balloon； made of oiled cotton and marvellously gas tight。 A steering apparatus was placed both fore and aft； and at a safe distance below the main structure were fixed； also forward and aft； on aluminium platforms； two Daimler motor engines of 16…horse power； working aluminium propellers of four blades at the rate of 1；000 revolutions a minute。 Finally； firmly attached to the inner framework by rods of aluminium； were two cars of the same metal； furnished with buffer springs to break the force of a fall。 The trial trip was not made till the summer followingJune； 1900and； in the meanwhile； experiments had gone forward with another mode of flight； terminating； unhappily； in the death of one of the most expert and ingenious of mechanical aeronauts。
Mr。 Percy S。 Pilcher； now thirty…three years of age； having received his early training in the Navy； retired from the Service to become a civil engineer； and had been for some time a partner in the firm of Wilson and Pilcher。 For four or five years he had been experimenting in soaring flight； using a Lilienthal machine； which he improved to suit his own methods。 Among these was the device of rising off the ground by being rapidly towed by a line against the wind。
At the end of September he gave an exhibition at Stamford Park before Lord Bray and a select party of friendsthis in spite of an unsuitable afternoon of unsteady wind and occasional showers。 A long towing line was provided； which； being passed round pulley blocks and dragged by a couple of horses； was capable of being hauled in at high speed。 The first trial； though ending in an accident； was eminently satisfactory。 The apparatus； running against the wind； had risen some distance； when the line broke； yet the inventor descended slowly and safely with outstretched wings。 The next trial also commenced well； with an easy rise to a height of some thirty feet。 At that point； however； the tail broke with a snap； and the machine； pitching over； fell a complete wreck。 Mr。 Pilcher was found insensible； with his thigh broken； and though no other serious injury was apparent； he succumbed two days afterwards without recovering consciousness。 It was surmised that shrinkage of the canvas of the tail； through getting wet； had strained and broken its bamboo stretcher。
This autumn died Gaston Tissandier； at the age of fifty…six； and in the month of December； at a ripe old age； while still in full possession of intellectual vigour； Mr。 Coxwell somewhat suddenly passed away。 Always keenly interested in the progress of aeronautics； he had but recently； in a letter to the Standard； proposed a well…considered and practical method of employing Montgolfier reconnoitring balloons； portable； readily inflated；
