the dominion of the air-第37节
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At the end of November； when over thirty escape voyages had been made； two fatal disasters occurred。 A sailor of the name of Prince ascended alone on a moonless night； and at dawn； away on the north coast of Scotland； some fishermen sighted a balloon in the sky dropping to the westward in the ocean。 The only subsequent trace of this balloon was a bag of despatches picked up in the Channel。 Curiously enough； two days later almost the same story was repeated。 Two aeronauts； this time in charge of despatches and pigeons； were carried out to sea and never traced。
Undeterred by these disasters； a notable escape was now attempted。 An important total eclipse of the sun was to occur in a track crossing southern Spain and Algeria on December 22nd。 An enthusiastic astronomer； Janssen； was commissioned by the Academy of Sciences to attend and make observations of this eclipse。 But M。 Janssen was in Paris； as were also his instruments； and the eclipse track lay nearly a thousand miles away。 The one and only possible mode of fulfilling his commission was to try the off…chance afforded by balloon； and this chance he resorted to only twenty days before the eclipse was due。
Taking with him the essential parts of a reflecting telescope； and an active young sailor as assistant； he left Paris at 6 a。m。 and rose at once to 3；600 feet； dipping again somewhat at sunrise （owing； as he supposed； to loss of heat through radiation）； but subsequently ascending again rapidly under the increased altitude of the sun till his balloon attained its highest level of 7；200 feet。 From this elevation； shortly after 11 a。m。； he sighted the sea； when he commenced a descent which brought him to earth at the mouth of the Loire。 It had been fast travellingsome 300 miles in little more than three hoursand the ground wind was strong。 Nevertheless； neither passengers nor instruments were injured； and M。 Janssen was fully established by the day of eclipse on his observing ground at Oran； on the Algerian coast。 It is distressing to add that the phenomenon was hidden by cloud。 In the month that followed this splendid venture no fewer than fifteen balloons escaped from Paris； of which four fell into the hands of the enemy； although for greater security all ascents were now being made by night。
On January 13th； 1871； a new device for the return post was tried； and； in addition to pigeons； sheep dogs were taken up； with the idea of their being returned to the city with messages concealed within their collars。 There is apparently no record of any message having been returned to the town by this ingenious method。 On January 24th a balloon； piloted by a sailor； and containing a large freight of letters； fell within the Prussian lines； but the patriotism of the country was strong enough to secure the despatches being saved and entrusted to the safe conveyance of the Post Office。 Then followed the total loss of a balloon at sea； but this was destined to be the last； save one； that was to attempt the dangerous mission。 The next day； January 28th； the last official balloon left the town； manned by a single sailor； carrying but a small weight of despatches； but ordering the ships to proceed to Dieppe for the revictualling of Paris。
Five additional balloons at that time in readiness were never required for the risky service for which they were designed。
There can be little doubt that had the siege continued a more elaborate use of balloons would have been developed。 Schemes were being mooted to attempt the vastly more difficult task of conveying balloons into Paris from outside。 When hostilities terminated there were actually six balloons in readiness for this venture at Lisle； and waiting only for a northerly wind。 M。 de Fonvielle； possessed of both courage and experience； was prepared to put in practice a method of guiding by a small propelling force a balloon that was being carried by sufficiently favouring winds within a few degrees of its desired goaland in the case of Paris the goal was an area of some twenty miles in diameter。 Within the invested area several attempts were actually made to control balloons by methods of steering。 The names of Vert and Dupuy de Lome must here be specially mentioned。 The former had elaborated an invention which received much assistance； and was subsequently exhibited at the Crystal Palace。 The latter received a grant of L1；600 to perfect a complex machine； having within its gas envelope an air chamber； suggested by the swimming bladder of a fish； having also a sail helm and a propelling screw； to be operated by manual labour。
The relation of this invention to others of similar purpose will be further discussed later on。 But an actual trial of a dirigible craft； the design of Admiral Labrousse； was made from the Orleans railway station on January 9th。 This machine consisted of a balloon of about the standard capacity of the siege balloons； namely some 70；000 cubic feet； fitted with two screws of about 12 feet diameter； but capable of being readily worked at moderate speed。 It was not a success。 M。 Richard； with three sailors； made a tentative ascent； and used their best endeavours to control their vessel； but practically without avail； and the machine presently coming to earth clumsily； a portion of the gear caught in the ground and the travellers were thrown over and roughly dragged for a long distance。
Fairly looked at； the aerial post of the siege of Paris must be regarded as an ambitious and； on the whole； successful enterprise。 Some two million and a half of letters； amounting in weight to some ten tons； were conveyed through the four months； in addition to which at least an equal weight of other freight was taken up； exclusive of actual passengers； of whom no fewer than two hundred were transported from the beleaguered city。 Of these only one returned； seven or eight were drowned； twice this number were taken prisoners； and as many again more or less injured in descents。 From a purely financial point of view the undertaking was no failure； as the cost； great as it necessarily became； was； it is said； fairly covered by the postage； which it was possible and by no means unreasonable to levy。 The recognised tariff seems to have been 20 centimes for 4 grammes； or at the rate of not greatly more than a shilling per English ounce。 Surely hardly on a par with famein prices in a time of siege。
It has already been stated that the defenders of Paris did not derive substantial assistance from the services of such a reconnoitring balloon as is generally used in warfare at every available opportunity。 It is possible that the peculiar circumstances of the investment of the town rendered such reconnaissance of comparatively small value。 But； at any rate； it seems clear that due opportunity was not given to this strategic method。 M。 Giffard； who at the commencement of the siege was in Paris； and whose experience with a captive balloon was second to none； made early overtures to the Government； offering to build for L40；000 a suitable balloon； capable of raising forty persons to a heightm of 3；000 feet。 Forty aerial scouts； it may be said； are hardly needed for purposes of outlook at one time； but it appears that this was not the consideration which stood in the way of M。 Giffard's offer being accepted。 According to M。 de Fonvielle； the Government refused the experienced aeronaut's proposal on the ground that he required a place in the Champs Elysees； 〃which it would be necessary to clear of a few shrubs〃！
CHAPTER XIX。 THE TRAGEDY OF THE ZENITH。〃THE NAVIGABLE BALLOON
The mechanical air ship had； by this time； as may be inferred； begun seriously to occupy the attention of both theoretical and practical aeronauts。 One of the earliest machines deserving of special mention was designed by M。 Giffard； and consisted of an elongated balloon； 104 feet in length and 39 feet in greatest diameter； furnished with a triangular rudder； and a steam engine operating a screw。 The fire of the engine； which burned coke； was skilfully protected； and the fuel and water required were taken into calculation as so much ballast to be gradually expended。 In this vessel； inflated only with coal gas； and somewhat unmanageable and difficult to balance； the enthusiastic inventor ascended alone from the Hippodrome and executed sundry desired movements； not unsuccessfully。 But the trial was not of long duration； and the descent proved both rapid and perilous。 Had the trial been made in such a perfect calm as that which prevailed when certain subsequent inventions were tested； it was considered that M。 Giffard's vessel would have been as navigable as a boat in the water。 This unrivalled mechanician； after having made great advances in the direction of high speed engines of sufficient lightness； proceeded to design a vastly improved dirigible balloon； when his endeavours were frustrated by blindness。
As has been already stated； M。 Dupuy de Lome； at the end of the siege of Paris； was engaged in building a navigable balloon； which； owing to the unsettled state of affairs in France； did not receive its trial till two years later。 This balloon； which was inflated with pure hydrogen； was of greater capacity than that of M。 Gif
