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bited。 First； the balloon being weighted so as to remain poised in the still air of the building； the mechanism was started； and the machine rose steadily to the ceiling。 The fans were then reversed； when the model； equally gracefully； descended to the floor。 Lastly； the balloon； with a weighted trail rope； being once more balanced in mid…air； the fans were applied laterally； when the machine would take a horizontal flight； pulling the trail rope after it； with an attached weight dragging along the floor until the mechanism had run down； when it again remained stationary。 The correspondent of the Times continues； 〃Mr。 Green states that by these simple means a voyage across the Atlantic may be performed in three or four days； as easily as from Vauxhall Gardens to Nassau。〃
We can hardly attribute this statement seriously to one who knew as well as did Green how fickle are the winds； and how utterly different are the conditions between the still air of a room and those of the open sky。 His insight into the difficulties of the problem cannot have been less than that of his successor； Coxwell； who； as the result of his own equally wide experience； states positively； 〃I could never imagine a motive power of sufficient force to direct and guide a balloon； much less to enable a man or a machine to fly。〃 Even when modern invention had produced a motive power undreamed of in the days we are now considering； Coxwell declares his conviction that inherent difficulties would not be overcome 〃unless the air should invariably remain in a calm state。〃
It would be tedious and scarcely instructive to inquire into the various forms of flying machines that were elaborated at this period； but one that was designed in America by Mr。 Henson； and with which it was seriously contemplated to attempt to cross the Atlantic； may be briefly described。 In theory it was supposed to be capable of being sustained in the air by virtue of the speed mechanically imparted to it； and of the angle at which its advancing under surface would meet the air。 The inventor claimed to have produced a steam engine of extreme lightness as well as efficiency； and for the rest his machine consisted of a huge aero…plane propelled by fans with oblique vanes； while a tail somewhat resembling that of a bird was added； as also a rudder； the functions of which were to direct the craft vertically and horizontally respectively。 Be it here recorded that the machine did not cross the Atlantic。
One word as to the instruments used up to this time for determining altitudes。 These were； in general； ordinary mercurial barometers； protected in various ways。 Green encased his instrument in a simple metal tube； which admitted of the column of mercury being easily read。 This instrument； which is generally to be seen held in his hand in Green's old portraits； might be mistaken for a mariner's telescope。 It is now in the possession of the family of Spencers； the grandchildren of his old aeronautical friend and colleague； and it is stated that with all his care the glass was not infrequently broken in a descent。
Wise； with characteristic ingenuity； devised a rough…and…ready height instrument； which he claims to have answered well。 It consisted simply of a common porter bottle； to the neck of which was joined a bladder of the same capacity。 The bottle being filled with air of the density of that on the ground； and the bladder tied on in a collapsed state； the expansion of the air in the bottle would gradually fill the bladder as it rose into the rarer regions of the atmosphere。 Experience would then be trusted to enable the aeronaut to judge his height from the amount of inflation noticeable in the bladder。
CHAPTER XII。 HENRY COXWELL AND HIS CONTEMPORARIES。
Mention should be made in these pages of a night sail of a hundred miles； boldly carried out in 1849 by M。 Arban； which took the voyager from Marseilles to Turin fairly over the Alps。 The main summit was reached at 11 p。m。； when the 〃snow； cascades； and rivers were all sparkling under the moon； and the ravines and rocks produced masses of darkness which served as shadows to the gigantic picture。〃 Arban was at one time on a level with the highest point of Mont Blanc； the top of which； standing out well above the clouds； resembled 〃an immense block of crystal sparkling with a thousand fires。〃
In London； in the year of the Great Exhibition； and while the building was still standing in Hyde Park； there occurred a balloon incident small in itself； but sufficient to cause much sensation at the crowded spot where it took place。 The ascent was made from the Hippodrome by Mr。 and Mrs。 Graham in very boisterous weather； and； on being liberated； the balloon seems to have fouled a mast； suffering a considerable rent。 After this the aeronauts succeeded in clearing the trees in Kensington Gardens； and in descending fairly in the Park； but； still at the mercy of the winds； they were carried on to the roof of a house in Arlington Street； and thence on to another in Park Place； where； becoming lodged against a stack of chimneys； they were eventually rescued by the police without any material damage having been done。
But this same summer saw the return to England of Henry Coxwell； and for some years the story of the conquest of the air is best told by following his stirring career； and his own comments on aeronautical events of this date。 We find him shortly setting about carrying out some reconnoitring and signalling experiments； designed to be of use in time of war。 This was an old idea of his； and one which had； of course； been long entertained by others； having； indeed； been put to some practical test in time of warfare。 It will be well to make note of what attention the matter had already received； and of what progress had been made both in theory and practice。
We have already made some mention in Chapter IV。 of the use which the French had made of balloons in their military operations at the end of the eighteenth and beginning of nineteenth the century。 It was； indeed； within the first ten years after the first invention of the balloon that； under the superintendence of the savants of the French Academy； a practical school of aeronautics was established at Meudon。 The names of Guyton； De Morveau （a distinguished French chemist）； and Colonel Coutelle are chiefly associated with the movement； and under them some fifty students received necessary training。 The practising balloon had a capacity of 17；000 cubic feet； and was inflated with pure hydrogen； made by what was then a new process as applied to ballooning； and which will be described in a future chapter。 It appears that the balloon was kept always full； so that any opportunity of calm weather would be taken advantage of for practice。 And it is further stated that a balloon was constructed so sound and impervious that after the lapse of two months it was still capable； without being replenished； of raising into the air two men； with necessary ballast and equipment。 The practical trial for the balloon in real service came off in June； 1794； when Coutelle in person； accompanied by two staff officers； in one of the four balloons which the French Army h