the mastery of the air(操纵空气)-第2节
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atmosphere which makes the smoke from chimneys and elsewhere rise in
opposition to the force of gravity？ If so； cannot we discover this power；
and apply it to the service of mankind？〃
We may imagine that such questions were in the minds of those two
French paper…makers； just as similar questions were in the mind of James
Watt when he was discovering the power of steam。 But one of the most
important attributes of an inventor is an infinite capacity for taking pains；
together with great patience。
And so we find the two brothers employing their leisure in what to us
would； be a childish pastime； the making of paper balloons。 The story tells
us that their room was filled with smoke； which issued from the windows
as though the house were on fire。 A neighbour； thinking such was the case；
rushed in； but； on being assured that nothing serious was wrong； stayed to
watch the tiny balloons rise a little way from the thin tray which contained
the fire that made the smoke with which the bags were filled。 The
experiments were not altogether successful； however； for the bags rarely
rose more than a foot or so from the tray。 The neighbour suggested that
they should fasten the thin tray on to the bottom of the bag； for it was
thought that the bags would not ascend higher because the smoke became
cool； and if the smoke were imprisoned within the bag much better results
would be obtained。 This was done； and； to the great joy of the brothers and
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their visitor； the bag at once rose quickly to the ceiling。
But though they could make the bags rise their great trouble was that
they did not know the cause of this ascent。 They thought； however； that
they were on the eve of some great discovery； and； as events proved； they
were not far wrong。 For a time they imagined that the fire they had used
generated some special gas； and if they could find out the nature of this
gas； and the means of making it in large quantities； they would be able to
add to their success。
Of course； in the light of modern knowledge； it seems strange that the
brothers did not know that the reason the bags rose； was not because of
any special gas being used； but owing to the expansion of air under the
influence of heat； whereby hot air tends to rise。 Every schoolboy above the
age of twelve knows that hot air rises upwards in the atmosphere； and that
it continues to rise until its temperature has become the same as that of the
surrounding air。
The next experiment was to try their bags in the open air。 Choosing a
calm； fine day； they made a fire similar to that used in their first
experiments； and succeeded in making the bag rise nearly 100 feet。 Later
on； a much larger craft was built； which was equally successful。
And now we must leave the experiments of the Montgolfiers for a
moment； and turn to the discovery of hydrogen gas by Henry Cavendish； a
well…known London chemist。 In 1766 Cavendish proved conclusively that
hydrogen gas was not more than one…seventh the weight of ordinary air。 It
at once occurred to Dr。 Black； of Glasgow； that if a thin bag could be filled
with this light gas it would rise in the air； but for various reasons his
experiments did not yield results of a practical nature for several years。
Some time afterwards； about a year before the Montgolfiers
commenced their experiments which we have already described； Tiberius
Cavallo； an Italian chemist； succeeded in making； with hydrogen gas；
soap…bubbles which rose in the air。 Previous to this he had experimented
with bladders and paper bags； but the bladders he found too heavy； and the
paper too porous。
It must not be thought that the Montgolfiers experimented solely with
hot air in the inflation of their balloons。 At one time they used steam； and；
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later on； the newly…discovered hydrogen gas； but with both these agents
they were unsuccessful。 It can easily be seen why steam was of no use；
when we consider that paper was employed； hydrogen； too； owed its lack
of success to the same cause for the porosity of the paper allowed the gas
to escape quickly。
It is said that the name 〃balloon〃 was given to these paper craft
because they resembled in shape a large spherical vessel used in chemistry；
which was known by that name。 To the brothers Montgolfier belongs the
honour of having given the name to this type of aircraft； which； in the two
succeeding centuries； became so popular。
After numerous experiments the public were invited to witness the
inflation of a particularly huge balloon； over 30 feet in diameter。 This was
accomplished over a fire made of wool and straw。 The ascent was
successful； and the balloon； after rising to a height of some 7000 feet； fell
to earth about two miles away。
It may be imagined that this experiment aroused enormous interest in
Paris； whence the news rapidly spread over all France and to Britain。 A
Parisian scientific society invited Stephen Montgolfier to Paris in order
that the citizens of the metropolis should have their imaginations excited
by seeing the hero of these remarkable experiments。 Montgolfier was not a
rich man； and to enable him to continue his experiments the society
granted him a considerable sum of money。 He was then enabled to
construct a very fine balloon； elaborately decorated and painted； which
ascended at Versailles in the presence of the Court。
To add to the value of this experiment three animals were sent up in a
basket attached to the balloon。 These were a sheep； a cock； and a duck。 All
sorts of guesses were made as to what would be the fate of the 〃poor
creatures〃。 Some people imagined that there was little or no air in those
higher regions and that the animals would choke； others said they would
be frozen to death。 But when the balloon descended the cock was seen to
be strutting about in his usual dignified way； the sheep was chewing the
cud； and the duck was quacking for water and worms。
At this point we will leave the work of the brothers Montgolfier。 They
had succeeded in firing the imagination of nearly every Frenchman； from
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King Louis down to his humblest subject。 Strange； was it not； though
scores of millions of people had seen smoke rise； and clouds float； for
untold centuries； yet no one； until the close of the eighteenth century；
thought of making a balloon？
The learned Franciscan friar； Roger Bacon； who lived in the thirteenth
century； seems to have thought of the possibility of producing a
contrivance that would float in air。 His idea was that the earth's
atmosphere was a 〃true fluid〃； and that it had an upper surface as the
ocean has。 He quite believed that on this upper surfacesubject； in his
belief； to waves similar to those of the seaan air…ship might float if it
once succeeded in rising to the required height。 But the difficulty was to
reach the surface of this aerial sea。 To do this he proposed to make a large
hollow globe of metal； wrought as thin as the skill of man could make it；
so that it might be as light as possible； and this vast globe was to be filled
with 〃liquid fire〃。 Just what 〃liquid fire〃 was； one cannot attempt to
explain； and it is doubtful if Bacon himself had any clear idea。 But he
doubtless thought of some gaseous substance lighter than air； and so he
would seem to have； at least； hit upon the principle underlying the
construction of the modern balloon。 Roger Bacon had ideas far in advance
of his time； and his experiments made such an impression of wonder on
the popular mind that they were believed to be wrought by black magic；
and the worthy monk was classed among those who were supposed to be
in league with Satan。
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