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deavours 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。 Giffard； being cigar shaped and measuring 118 feet by 48 feet。 It was also provided with an ingenious arrangement consisting of an internal air bag； capable of being either inflated or discharged； for the purpose of keeping the principal envelope always distended； and thus offering the least possible resistance to the wind。 The propelling power was the manual labour of eight men working the screw； and the steerage was provided for by a triangular rudder。 The trial； which was carried out without mishap； took place in February； 1872； in the Fort of Vincennes； under the personal direction of the inventor； when it was found that the vessel readily obeyed the helm； and was capable of a speed exceeding six miles an hour。
It was not till nine years after this that the next important trial with air ships was made。 The brothers Tissandier will then be found taking the lead； and an appalling incident in the aeronautical career of one of these has now to be recorded。
In the spring of 1875； and with the co…operation of French scientific societies； it was determined to make two experimental voyages in a balloon called the 〃Zenith；〃 one of these to be of long duration； the other of great height。 The first of these had been successfully accomplished in a flight of twenty…four hours' duration from Paris to Bordeaux。 It was now April the 15th； and the lofty flight was embarked upon by M。 Gaston Tissandier； accompanied by MM。 Croce…Spinelli and Sivel。 Under competent advice； provision for respiration on emergency was provided in three small balloons； filled with a mixture of air and oxygen； and fitted with indiarubber hose pipes； which would allow the mixture； when inhaled； to pass first through a wash bottle containing aromatic fluid。 The experiments determined on included an analysis of the proportion of carbonic acid gas at different heights by means of special apparatus； spectroscopic observations； and the readings registered by certain barometers and thermometers。 A novel and valuable experiment； also arranged； was that of testing the internal temperature of the balloon as compared with that of the external air。
Ascending at 11。30 a。m。 under a warm sun； the balloon had by 1 p。m。 reached an altitude of 16；000 feet； when the external air was at freezing point； the gas high in the balloon being 72 degrees； and at the centre 66 degrees。 Ere this height had been fully reached； however； the voyagers had begun to breathe oxygen。 At 11。57； an hour previously； Spinelli had written in his notebook； 〃Slight pain in the earssomewhat oppressedit is the gas。〃 At 23；000 feet Sivel wrote in his notebook； 〃I am inhaling oxygenthe effect is excellent；〃 after which he proceeded to urge the balloon higher by a discharge of ballast。 The rest of the terrible narrative has now to be taken from the notes of M。 Tissandier； and as these constitute one of the most thrilling narratives in aeronautical records we transcribe them nearly in full； as given by Mr。 Glaisher：
〃At 23；000 feet we were standing up in the car。 Sivel； who had given up for a moment； is re…invigorated。 Croce…Spinelli is motionless in f