At this point we must, for a brief while, drop the history of the famous aeronaut whose early career we have been briefly sketching in the last chapter, and turn our attention to a new feature of English ballooning. We have, at last, to record some genuinely scientific ascents, which our country now, all too tardily, instituted. It was the British Association that took the initiative, and the two men they chose for their purpose were both exceptionally qualified for the task they had in hand. The practical balloonist was none other than the veteran Charles Green, now in his sixty-seventh year, but destined yet to enjoy nearly twenty years more of life. The scientific expert was Mr. John Welsh, well fitted for the projected work by long training at Kew Observatory. The balloon which they used is itself worthy of mention, being the great Nassau Balloon of olden fame.

Welsh was quick to realise more clearly than any former experimentalist that on account of the absence of breeze in a free balloon, as also on account of great solar radiation, the indications of thermometers would, without special precautions, be falsified. He therefore invented a form of aspirating thermometer, the earliest to be met with, and far in advance of any that were subsequently used by other scientists. It consisted of a polished tube, in which thermometers were enclosed, and through which a stream of air was forced by bellows.

The difficulty of obtaining really accurate readings where thermometers are being quickly transported through varying temperatures is generally not duly appreciated. In the case of instruments carried m a balloon it should be remembered that the balloon itself conveys, clinging about it, no inconsiderable quantity of air, brought from other levels, while the temperature of its own mass will be liable to affect any thermometer in close neighbourhood. Moreover, any ordinary form of thermometer is necessarily sluggish in action, as may be readily noticed. If, for example, one be carried from a warm room to a cold passage, or vice versa it will be seen that the column moves very deliberately, and quite a long interval will elapse before it reaches its final position, the cause being that the entire instrument, with any stand or mounting that it may have, will have to adapt itself to the change of temperature before a true record will be obtained. This difficulty applies unavoidably to all thermometers in some degree, and the skill of instrument makers has been taxed to reduce the errors to a minimum. It is necessary, in any case, that a constant stream of surrounding air should play upon the instrument, and though this is most readily effected when instruments are carried aloft by kites, yet even thus it is thought that an interval of some minutes has to elapse before any form of thermometer will faithfully record any definite change of temperature. It is on this account that some allowance must be made for observations which will, in due place, be recorded of scientific explorers; the point to be borne in mind being that, as was mentioned in a former chapter, such observations will have to be regarded as giving readings which are somewhat too high in ascents and too low in descents. Two forms of thermometers at extremely simple construction, yet possessed of great sensibility, will be discussed in later chapters.

The thermometers that Welsh used were undoubtedIy far superior to any that were devised before his time and it is much to be regretted that they were allowed to fall into disuse. Perhaps the most important stricture on the observations that will have to be recorded is that the observers were not provided with a base station, on which account the value of results was impaired. It was not realised that it was necessary to make observations on the ground to compare with those that were being made at high altitudes.

Welsh made, in all, four ascents in the summer and autumn of 1852 and in his report he is careful to give the highest praise to his colleague, Green, whose control over his balloon he describes as "so complete that none who accompanied him can be otherwise than relieved from all apprehension, and free to devote attention calmly to the work before him."

The first ascent was made at 3.49 p.m. on August the 17th, under a south wind and with clouds covering some three-quarters of the sky. Welsh's first remark significant, and will be appreciated by anyone who has attempted observational work in a balloon. He states naively that "a short time was lost at first in an attempt to put the instruments into more convenient order, and also from the novelty of the situation." Then he mentions an observation which, in the experience of the writer, is a common one. The lowest clouds, which were about 2,500 feet high and not near the balloon, were passed without being noticed; other clouds were passed at different heights; and, finally, a few star-shaped crystals of snow; but the sun shone almost constantly. Little variation occurred in the direction of travel, which averaged thirty-eight miles an hour, and the descent took place at 5.20 p.m. at Swavesey, near Cambridge.

The second ascent took place at 4.43 p.m. on August 26th, under a gentle east wind and a partially obscured sky. The clouds were again passed without being perceived. This was at the height of 3,000 feet, beyond which was very clear sky of deep blue. The air currents up to the limits of 12,000 feet set from varying directions. The descent occurred near Chesham at 7.45 p.m.

The third ascent, at 2.35 p.m. on October the 21st was made into a sky covered with dense cloud masses lying within 3,000 and 3,700 feet. The sun was then seen shining through cirrus far up. The shadow of the balloon was also seen on the cloud, fringed with a glory, and about this time there was seen "stretching for a considerable length in a serpentine course, over the surface of the cloud, a well-defined belt, having the appearance of a broad road."

Being now at 12,000 feet, Green thought it prudent to reconnoitre his position, and, finding they were near the sea, descended at 4.20 p.m. at Rayleigh, in Essex. Some important notes on the polarisation of the clouds were made.

The fourth and final voyage was made in a fast wind averaging fifty knots from the north-east. Thin scud was met at 1,900 feet, and an upper stratum at 4,500 feet, beyond which was bright sun. The main shift of wind took place just as the upper surface of the first stratum was reached. In this ascent Welsh reached his greatest elevation, 22,930 feet, when both Green and himself experienced considerable difficulty in respiration and much fatigue. The sea being now perceived rapidly approaching, a hasty descent was made, and many of the instruments were broken.

In summarising his results Welsh states that "the temperature of the air decreases uniformly with height above the earth's surface until at a certain elevation, varying on different days, decrease is arrested, and for the space of 2,000 or 3,000 feet the temperature remains nearly constant, or even increases, the regular diminution being again resumed and generally maintained at a rate slightly less rapid than in the lower part of the atmosphere, and commencing from a higher temperature than would have existed but for the interruption noticed." The analysis of the upper air showed the proportion of oxygen and nitrogen to vary scarcely more than at different spots on the earth.

As it is necessary at this point to take leave of the veteran Green as a practical aeronaut, we may here refer to one or two noteworthy facts and incidents relating to his eventful career. In 1850 M. Poitevin is said to have attracted 140,000 people to Paris to look at an exhibition of himself ascending in a balloon seated on horseback, after which Madame Poitevin ascended from Cremorne Gardens in the same manner, the exhibition being intended as a representation of "Europa on a Bull." This, however, was discountenanced by the authorities and withdrawn. The feats were, in reality, merely the repetitions of one that had been conceived and extremely well carried out by Green many years before - as long ago, in fact, as 1828, when he arranged to make an ascent from the Eagle Tavern, City Road, seated on a pony. To carry out his intention, he discarded the ordinary car, replacing it with a small platform, which was provided with places to receive the pony's feet; while straps attached to the hoop were passed under the animal's body, preventing it from lying down or from making any violent movement. This the creature seemed in no way disposed to attempt, and when all had been successfully carried out and an easy descent effected at Beckenham, the pony was discovered eating a meal of beans with which it had been supplied.

Several interesting observations have been recorded by Green on different occasions, some of which are highly instructive from a practical or scientific point of view. On an ascent from Vauxhall, in which he was accompanied by his friend Spencer and Mr. Rush, he recorded how, as he constantly and somewhat rapidly rose, the wind changed its direction from N.W. through N. to N.E., while he remained over the metropolis, the balloon all the while rotating on its axis. This continual swinging or revolving of the balloon Green considers an accompaniment of either a rapid ascent or descent, but it may be questioned whether it is not merely a consequence of changing currents, or, sometimes, of an initial spin given inadvertently to the balloon at the moment of its being liberated. The phenomenon of marked change which he describes in the upper currents is highly interesting, and tallies with what the writer has frequently experienced over London proper. Such higher currents may be due to natural environment, and to conditions necessarily prevailing over so vast and varied a city, and they may be able to play an all-important part in the dispersal of London smoke or fog. This point will be touched on later. In this particular voyage Green records that as he was rising at the moment when his barometer reached 19 inches, the thermometer he carried registered 46 degrees, while on coming down, when the barometer again marked 19 inches, the same thermometer recorded only 22 degrees. It will not fail to be recognised that there is doubtless here an example of the errors alluded to above, inseparable from readings taken in ascent and descent.

A calculation made by Green in his earlier years has a certain value. By the time he had accomplished 200 ascents he was at pains to compute that he had travelled across country some 6,000 miles, which had been traversed in 240 hours. From this it would follow that the mean rate of travel in aerial voyages will be about twenty-five miles per hour. Towards the end of his career we find it stated by Lieutenant G. Grover, R.E., that "the Messrs. Green, Father and Son, have made between them some 930 ascents, in none of which have they met with any material accident or failure." This is wonderful testimony, indeed, and we may here add the fact that the father took up his own father, then at the age of eighty-three, in a balloon ascent of 1845, without any serious consequences. But it is time that some account should be given of a particular occasion which at least provided the famous aeronaut with an adventure spiced with no small amount of risk. It was on the 5th of July, 1850, that Green ascended, with Rush as his companion, from Vauxhall, at the somewhat late hour of 7.50 p.m., using, as always, the great Nassau balloon. The rate of rise must have been very considerable, and they presently record an altitude of no less than 20,000 feet, and a temperature of 12 degrees below freezing. They were now above the clouds, where all view of earth was lost, and, not venturing to remain long in this situation, they commenced a rapid descent, and on emerging below found themselves sailing down Sea Reach in the direction of Nore Sands, when they observed a vessel. Their chance of making land was, to say the least, uncertain, and Green, considering that his safety lay in bespeaking the vessel's assistance, opened the valve and brought the car down in the water some two miles north of Sheerness, the hour being 8.45, and only fifty-five minutes since the start. The wind was blowing stiffly, and, catching the hollow of the half-inflated balloon, carried the voyagers rapidly down the river, too fast, indeed, to allow of the vessel's overtaking them. This being soon apparent, Green cast out his anchor, and not without result, for it shortly became entangled in a sunken wreck, and the balloon was promptly "brought up," though struggling and tossing in the broken water. A neighbouring barge at once put off a boat to the rescue, and other boats were despatched by H.M. cutter Fly, under Commander Gurling. Green and Rush were speedily rescued, but the balloon itself was too restive and dangerous an object to approach with safety. At Green's suggestion, therefore, a volley of musketry was fired into the silk' after which it became possible to pass a rope around it and expel the gas. Green subsequently relates how it took a fortnight to restore the damage, consisting of sixty-two bullet rents and nineteen torn gores.

Green's name will always be famous, if only for the fact that it was he who first adopted the use of coal gas in his calling. This, it will be remembered, was in 1821, and it should be borne in mind that at that time household gas had only recently been introduced. In point of fact, it first lighted Pall Mall in 1805, and it was not used for the general lighting of London till 1814.

We are not surprised to find that the great aeronaut at one time turned his attention to the construction of models, and this with no inconsiderable success. A model of his was exhibited in 1840 at the Polytechnic Institution, and is described in the Times as consisting of a miniature balloon of three feet diameter, inflated with coal gas. It was acted on by fans, which were operated by mechanism placed in the car. A series of three experiments was exhibited. 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.