the dominion of the air-第14部分
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In 1840； three years after the tragic adventure connected with Mr。 Cocking's parachute trial； we find Charles Green giving his views as to the practicability of carrying out a ballooning enterprise which should far excel all others that had hitherto been attempted。 This was nothing less than the crossing of the Atlantic from America to England。 There is no shadow of doubt that the adventurous aeronaut was wholly in earnest in the readiness he expressed to embark on the undertaking should adequate funds be forthcoming； and he discusses the possibilities with singular clearness and candour。 He maintains that the actual difficulties resolve themselves into two only： first； the maintenance of the balloon in the sky for the requisite period of time； and； secondly； the adequate control of its direction in space。 With respect to the first difficulty； he points out the fact to which we have already referred； namely； that it is impossible to avoid the fluctuations of level in a balloon's course； 〃by which it constantly becomes alternately subjected to escape of gas by expansion； and consequent loss of ballast； to furnish an equivalent diminution of weight。〃 Taking his own balloon of 80；000 cubic feet by way of example； he shows that this； fully inflated on the earth； would lose 8；000 cubic feet of gas by expansion in ascending only 3；000 feet。 Moreover； the approach of night or passage through cloud or falling rain would occasion chilling of the gas or accumulation of moisture on the silk； in either case necessitating the loss of ballast； the store of which is always the true measure of the balloon's life。
To combat the above difficulty Green sanguinely relies on his favourite device of a trail or guide rope； whose function； being that of relieving the balloon of a material weight as it approaches the earth； could； he supposed； be made to act yet more efficiently when over the sea in the following manner。 Its length； suspended from the ring； being not less than 2；000 feet； it should have attached at its lower end at certain intervals a number of small； stout waterproof canvas bags； the apertures of which should be contrived to admit water； but to oppose its return。 Between these bags were to be conical floats； to support any length of the rope that might descend on the sea。 Now； should the balloon commence descending； it would simply deposit a certain portion of rope on the water until it regained equilibrium at no great decrease of altitude； and would thus continue its course until alteration of conditions should cause it to recommence rising； when the weight of water now collected in the bags would play its part in preventing the balloon from soaring up into space。 With such a contrivance Green allowed himself to imagine that he could keep a properly made balloon at practically the same altitude for a period of three months if required。
The difficulty of maintaining a due course was next discussed； and somewhat speedily disposed of。 Here Green relied on the results of his own observation； gathered during 275 ascents； and stated his conviction that there prevails a uniformity of upper wind currents that would enable him to carry out his bold projects successfully。 His contention is best given in his own words：？
〃Under whatever circumstances；〃 he says； 〃I made my ascent； however contrary the direction of the winds below； I uniformly found that at a certain elevation； varying occasionally； but always within 10；000 feet of the earth； a current from the west or rather from the north of west； invariably travailed； nor do I recollect a single instance in which a different result ensued。〃 Green's complete scheme is now sufficiently evident。 He was to cross the Atlantic practically by the sole assistance of upper currents and his guide rope； but on this latter expedient； should adverse conditions prevail； he yet further relied； for he conceived that the rope could have attached to its floating end a water drag； which would hold the balloon in check until favouring gales returned。
Funds； apparently； were not forthcoming to allow of Mr。 Green's putting his bold method to the test； but we find him still adhering with so much zeal to his project that； five years later； he made； though again unsuccessfully； a second proposal to cross the Atlantic by balloon。 He still continued to make many and most enterprising ascents； and one of a specially sensational nature must be briefly mentioned before we pass on to regard the exploits of other aeronauts。
It was in 1841 on the occasion of a fete at Cremorne House； when Mr。 Green； using his famous Nassau balloon； ascended with a Mr。 Macdonnell。 The wind was blowing with such extreme violence that Rainham； in Essex； about twenty miles distant； was reached in little more than a quarter of an hour； and here； on nearing the earth； the grapnel； finding good hold； gave a wrench to the balloon that broke the ring and jerked the car completely upside down； the aeronauts only escaping precipitation by holding hard to the ropes。 A terrific steeplechase ensued； in which the travellers were dragged through stout fencing and other obstacles till the balloon； fairly emptied of gas； finally came to rest； but not until some severe injuries had been received。
CHAPTER VIII。 JOHN WISETHE AMERICAN AERONAUT。
By this period the domination of the air was being pursued in a fresh part of the world。 England and her Continental neighbours had vied with each in adding to the roll of conquests； and it could hardly other be supposed that America would stand by without taking part in the campaign which was now being revived with so much fresh energy in the skies。
The American champion who stepped forward was Mr。 John Wise； of Lancaster； Pa。； whose career； commencing in the year 1835； we must now for a while follow。 Few attempts at ballooning of any kind had up to that time been made in all America。 There is a record that in December； 1783； Messrs。 Rittenhouse and Hopkins； Members of the Philosophical Academy of Philadelphia； instituted experiments with an aerial machine consisting of a cage to which forty…seven small balloons were harnessed。 In this strange craft a carpenter； by name Wilcox； was induced to ascend； which； it is said； he did successfully； remaining in the air for ten minutes； when； finding himself near a river； he sought to come to earth again by opening several of his balloons。 This brought about an awkward descent； attended； however； by no more serious accident than a dislocated wrist。 Mr。 Wise； on the other hand； states that Blanchard had won the distinction of making the first ascent in the New World in 1793 in Philadelphia on which occasion Washington was a spectator； and a few years afterwards other Frenchmen gave ex hibitions； which； however； led to no real development of the new art on this； the further side of the Atlantic。 Thus the endeavours we are about to describe were those of an independent and； at the same time； highly； practical experimentalist； and on this account have a special value of their own。
The records that Wise has left of his investigations begin at the earliest stage； and possess the charm of an obvious and somewhat quaint reality。 They commence with certain crude calculations which would seem to place no limit to the capabilities of a balloon。 Thus； he points out that one of 〃the very moderate size of 400 feet diameter〃 would convey 13；000 men。 〃No wonder； then；〃 he continues； 〃the citizens of London became alarmed during the French War； when they mistook the appearance of a vast flock of birds coming towards the Metropolis for Napoleon's army apparently coming down upon them with this new contrivance。〃
Proceeding to practical measures； Wise's first care was to procure some proper material of which to build an experimental balloon of sufficient size to lift and convey himself alone。 For this he chose ordinary long…cloth； rendered gas…tight by coats of suitable varnish； the preparation of which became with him； as； indeed； it remains to this day； a problem of chief importance and difficulty。 Perhaps it hardly needs pointing out that the varnish of a balloon must not only be sufficiently elastic not to crack or scale off with folding or unavoidable rough usage； but it must also be of a nature to resist the common tendency of such substances to become adherent or 〃tacky。〃 Wise determined on bird lime thinned with linseed oil and ordinary driers。 With this preparation he coated his material several times both before and after the making up； and having procured a net； of which he speaks with pride； and a primitive sort of car； of which he bitterly complains； he thought himself sufficiently equipped to embark on an actual ascent； which he found a task of much greater practical difficulty than the mere manufacture of his air ship。 For the inflation by hydrogen of so small a balloon as his was he made more than ample provision in procuring no less than fifteen casks of 130 gallons capacity each。 He also duly secured a suitable filling ground at the corner of Ninth and Green Streets； Philadelphia； but he made a miscalculation as to the time the inflation would demand； and this led to unforeseen complications； for as yet he knew not the way of a crowd which comes to witness a balloon ascent。
Having all things in readiness； and prudently waiting for fair weather； he embarked on his grand experiment on the 2nd of May； 1835； announcing 4 p。m。 as the hour of departure。 But by that time the inflation； having only proceeded for three hours； the balloon was but half full； and then the populace began to behave as in such circumstances they always will。 They were incredulous； and presently grew troublesome。 In vain the harnessing of the car was proceeded with as though all were well。 For all was not well； and when the aeronaut stepped into his car with only fifteen pounds of sand and a few instruments he must have done so with much misgiving。 Still； he had friends around who might have been useful had they been less eager to help。 But these simply crowded round him； giving him no elbow room； nor opportunity for trying the 〃lift〃 of his all…too…empty globe。 Moreover； some would endeavour to throw the machine upward； while others as strenuously str
