CHAPTER III

BALLOONS--NOTABLE ASCENTS AND RESULTS OBTAINED--CAPTIVE BALLOONS

In the first chapter the invention of the hot-air and the hydrogen balloon was chronicled, and it was stated that on December 1, 1783, Charles rose from Paris to a height of 9000 feet. Public interest in France was greatly excited by this wonderful extension of the realm of man, and numerous ascensions with _MontgolfiËres_ and _CharliËres_, as the hot-air and hydrogen balloons were respectively called, took place in Paris and the provinces. The uses of the balloon seemed innumerable, and Lavoisier was instructed by the Academy of Sciences to draw up a report on the value of the new discovery. After having described in detail the ascensions which he had witnessed, the great chemist stopped, appalled at the multitude of problems which the balloon could solve. History has shown, however, that no commercial application of the balloon was possible, and that aside from its spectacular attractions, its chief use has been for scientific observations.

The first persons in England who devoted themselves to aÎrial navigation were foreigners. Two of them were Italians, the philosopher Tiberius Cavallo, who already in 1782 had showed to a London assembly that soap-bubbles filled with hydrogen will rise, and therefore had almost anticipated the invention of the hydrogen balloon, and the diplomatist Vincent Lunardi, who made some daring balloon ascents in 1784. But the honour of making the first scientific balloon voyage is due to a Bostonian, Dr. John Jeffries. Dr. Jeffries graduated at Harvard College in 1763 and then practised medicine in England, where he became a loyalist, and during the Revolution was with the British troops. In London he interested himself in aerostation, and, aided by the Royal Society, ascended in a balloon because, he said, "I wished to see the following points more clearly determined: first, the power of ascending or descending at pleasure, while suspended and floating in the air; secondly, the effect which oars or wings might be made to produce towards the purpose and in directing the course of the balloon; thirdly, the state and temperature of the atmosphere at different heights from the earth; and fourthly, by observing the varying course of the currents of air, or winds, at certain elevations, to throw some new light on the theory of winds in general." A French professional aeronaut named Blanchard had made three ascents in France and one in England, and Dr. Jeffries paid one hundred guineas to accompany Blanchard on his fifth ascent, which was made from London November 30, 1784. He took with him a thermometer, a barometer, a hygrometer, an electrometer, and a mariner's compass, also several numbered bottles, filled with water and provided with glass stoppers, which were to be emptied and corked up at different heights in the atmosphere. It was arranged to record the observations on ruled paper with a silver pen, because the doctor would not trust a common pen or pencil as liable to accident. He also had a map of England to determine the direction which the balloon took. Jeffries' English sentiments are shown by this quotation from his narrative: "I had provided a handsome British flag, invidiously represented the next day in one of the public papers to have been the flag of the American States." The barometer and thermometer were observed every few minutes, and the hygrometer occasionally. The electrometer did not change its indications. Samples of air were obtained and sent to the Royal Society, but it does not appear that they were ever analyzed. The balloon rose nearly two miles, and descended safely in Kent after an hour and a half. Jeffries' observations compare favourably with those made until recently; indeed, for nearly a century there was little improvement in the apparatus. The decrease of temperature which Jeffries found, viz. 1∞ for 360 feet rise, and the decreasing humidity with height agree very well with later observations.

Jeffries and Blanchard undertook a more perilous voyage on January 7, 1785, from Dover across the Channel, landing in the province of Artois, after, so runs the announcement, "we were suspended and floating in the atmosphere two hours over the sea and forty-seven minutes over the land of France." The voyagers were cordially welcomed, and were entertained lavishly in Paris as being, Jeffries says, "the first who passed across the sea from England into France by the route of the air." No instruments but a barometer and a compass were carried, and the only scientific result worthy of notice was that the balloon seemed to lose buoyancy over the sea, due to what Jeffries thought might be "the power of attraction over the water." The height of the balloon was measured trigonometrically by French officers in Calais, who found by angular measures, when the balloon was midway across the Channel, that its height was 4500 feet. Jeffries' voyages have been described somewhat at length because the first scientific balloon voyage is generally attributed to the Belgian physicist, Robertson, who ascended from Hamburg in 1803 to the improbable height of 24,000 feet. Robertson made his third ascent the next year from St. Petersburg, accompanied by the Academician Sacharoff. This was a scientific voyage, instituted at the request of the Russian Academy, to ascertain the physical state of the atmosphere and the component parts of it at different heights, also the difference between the results of vertical ascents and the observations of Deluc, De Saussure, von Humboldt and others on mountains, which it was rightly concluded could not be so free from terrestrial influences as those made in the open air. Among the experiments which the Academy proposed were the following: change of rate of evaporation of fluids, decrease or increase in the magnetic force, inclination of the magnetic needle, increase of heat of the solar rays, fainter colours in the spectrum, influence of rarefaction of the air on the human body, as well as some other chemical and philosophical experiments. A height of about two miles was reached, and many interesting observations were made, but since the instruments were not easily used in the basket of the balloon, the results were unsatisfactory and required repetition to be conclusive.

The Academy of Sciences of Paris now took up the investigation with the special object of proving whether the magnetic force decreased as Robertson in a balloon and De Saussure in the Alps had supposed. Two young physicists, Biot and Gay-Lussac, were chosen to carry out the investigations. They ascended from Paris on August 24, 1804, provided with all necessary instruments, but the balloon was too small to rise higher than 13,000 feet. Gay-Lussac ascended alone to a height of 23,000 feet on September 16, 1804, in a balloon filled with hydrogen. His observations confirmed those which he had made with Biot, that there was no change in the magnetic force, and from samples of air collected he proved that the chemical constitution of the air is invariable. His observations of temperature seemed to confirm the theory of a decline of temperature of 1∞ in 300 feet of elevation. The air was found to be very dry, and Gay-Lussac noticed that at the highest altitude the clouds were still far above him.

Passing over several notable ascents in other countries, it was not until 1850 that scientific ballooning was begun again in the land where the balloon originated. Then MM. Barral and Bixio made two ascents from Paris in rainy weather to the heights of 19,000 and 23,000 feet respectively, although they had expected to attain twice these altitudes. Their most interesting observations were the great thickness of the cloud mass, which in one case amounted to 15,000 feet, and the sudden fall of temperature in it from +15∞ to -39∞. Some curious optical phenomena were connected with the floating ice crystals, and although the light of the sky was found to be strongly polarized, the light reflected from the clouds was not polarized.

The field of operations was now transferred to England, where, under the auspices of the British Association, four ascents were made by John Welsh of the Kew Observatory in the great _Nassau_ balloon managed by Green, the veteran aeronaut. The special object of these investigations, like those in France, was the determination of the temperature and hygrometric condition of the air at different elevations. Besides this, samples of air at different heights were collected for analysis and the light reflected from clouds was examined for polarization. Recognizing that on account of the calm prevailing in the car of the balloon and the great solar radiation, the readings of the thermometer would be affected, Welsh enclosed the thermometers in polished tubes through which air was forced by bellows. This was the first aspirated thermometer, which alone gives the true temperature of the air with the conditions prevailing in a balloon. The instrument fell into oblivion until a few years ago, and to this fact is due the fictitious temperatures generally obtained by aeronauts. Welsh reached heights of from 12,500 to 23,000 feet, and his observations showed that the temperature of the air decreased uniformly with height until at a certain elevation, varying on different days, the decrease is arrested, and for a space of 2000 or 3000 feet the temperature remains nearly constant, or even increases slightly; the regular diminution being afterwards resumed and generally maintained at a less rapid rate than in the lower air, and commencing from a higher temperature than would have existed but for the interruption. The variation of the decrease with the seasons was also demonstrated. The humidity did not change much with height, and it was nowhere very dry. Finally, the light of the clouds was proved not to be polarized, and the permanent composition of the atmosphere was confirmed.

In 1861 another grant of money was made by the British Association for balloon experiments to be performed, under the direction of a Committee, by Mr. James Glaisher, then engaged in geodetic and meteorological work in England. Between 1862 and 1868 Glaisher, accompanied by the aeronaut Coxwell, made thirty ascents. They attained three times a height exceeding 23,000 feet, and once more than 29,000 feet, when they believed that the balloon rose to 37,000 feet. The primary objects of Glaisher's experiments were as follows: determination of the temperature of the air and its hygrometrical conditions up to five miles, comparisons of an aneroid barometer with a mercurial one, determination of the electrical state of the air and of its oxygenic state by means of ozone papers, time of vibration of a magnet at different distances from the earth. Secondary objects of study were the composition of the air, the form and thickness of clouds, the atmospheric currents, acoustical phenomena, etc. In order to obtain many observations frequent ascents were necessary, as the insular position of England precluded long voyages. During 1869 ascents in a captive balloon up to 1700 feet supplemented the employment of the free balloon, which from its rapid rise and fall made observations in it near the earth impossible. Glaisher was a good observer; his instruments were excellent, and had been previously tested, but their exposure in the basket of the balloon was bad, and although the thermometer was provided with an aspirator similar to Welsh's, Glaisher, noticing that the readings agreed with those of a freely exposed thermometer, hastily concluded that the use of the aspirator was unnecessary, and so discarded it.

Until quite recently Glaisher's results were accepted as representing the conditions of the free air up to the greatest height which it was possible to reach. These results showed that the temperature did not fall uniformly with height, but that it fell most rapidly near the earth and much less rapidly at great heights. In cloudy weather up to the height of a mile the mean decrease of temperature in the day-time differed little from the theory of 1∞ per 300 feet, but in clear or partly clear weather the decrease was more rapid, commencing with 1∞ for 160 feet near the ground and diminishing to 1∞ for 1000 feet at an elevation exceeding six miles. The observations in the captive balloon up to a third of a mile indicated a daily range in the vertical decrease of temperature. The observations of relative humidity agreed with Welsh's in showing a slight increase up to about half-a-mile, then a decrease up to above five miles, where there seemed to be an almost entire absence of water. The other observations were inconclusive, except that the time of vibration of a magnet was found to be somewhat longer than on the earth, which was contrary to Gay-Lussac's experience. The most remarkable of Glaisher's ascents was made from Wolverhampton on September 5, 1862, when in less than one hour he had passed the altitude of five miles, exceeding the greatest height hitherto reached. To quote from Glaisher's narrative: "Up to this time I had taken observations with comfort and experienced no difficulty in breathing, whilst Mr. Coxwell, in consequence of the exertion he had to make, had breathed with difficulty for some time. Having discharged sand, we ascended still higher; the aspirator became troublesome to work, and I also found a difficulty in seeing clearly.... About 1 hour 52 min., or later, I read the dry-bulb thermometer as minus 5∞; after this I could not see the column of mercury in the wet-bulb thermometer, nor the hands of the watch, nor the fine divisions of any instrument. I asked Mr. Coxwell to help me to read the instruments. In consequence, however, of the rotatory motion of the balloon, which had continued without ceasing since leaving the earth, the valve-line had become entangled, and he had to leave the car and mount into the ring to readjust it. I then looked at the barometer, and found its reading to be 9-3/4 inches, still decreasing fast, and implying a height exceeding 29,000 feet. Shortly after, I laid my arm upon the table, possessed of its full vigour, but on being desirous of using it, I found it powerless.... Trying to move the other arm, I found it powerless also. Then I tried to shake myself and succeeded, but I seemed to have no limbs.... I dimly saw Mr. Coxwell, and endeavoured to speak, but could not. In an instant intense darkness overcame me, so that the optic nerve lost power suddenly, but I was still conscious, with as active a brain as at the present moment whilst writing this. I thought I had been seized with asphyxia, and believed I should experience nothing more, as death would come unless we speedily descended; other thoughts were entering my mind, when I suddenly became unconscious.... I cannot tell anything of the sense of hearing, as no sound reaches the air to break the perfect stillness and silence of the regions between six and seven miles above the earth. My last observation was made at 1 hour 54 min., above 29,000 feet.... Whilst powerless I heard the words, 'temperature' and 'observation,' and I knew Mr. Coxwell was in the car speaking to and endeavouring to rouse me.... I then heard him speak more emphatically, but could not see, speak, or move. I heard him again say, 'Do try; now do!' Then the instruments became dimly visible, then Mr. Coxwell, and very shortly I saw clearly.... Mr. Coxwell told me that while in the ring he felt it piercingly cold, that hoarfrost was all round the neck of the balloon, and that on attempting to leave the ring he found his hands frozen. He had, therefore, to place his arms on the ring and drop down.... He wished to approach me, but could not; and when he felt insensibility coming over him too, he became anxious to open the valve. But in consequence of having lost the use of his hands he could not do this; ultimately he succeeded, by seizing the cord with his teeth, and dipping his head two or three times, until the balloon took a decided turn downwards. No inconvenience followed my insensibility; and when we dropped, it was in a country where no conveyance of any kind could be obtained, so I had to walk between seven and eight miles.... I have already said that my last observation was made at a height of 29,000 feet; at this time (1 hour 54 min.) we were ascending at the rate of 1000 feet per minute; and when I resumed observations we were descending at the rate of 2000 feet per minute. These two positions must be connected, taking into account the interval of time between, viz. 13 minutes, and on these considerations the balloon must have attained the altitude of 36,000 or 37,000 feet. Again, a very delicate minimum thermometer read minus 11∞.9, and this would give a height of 37,000 feet. Mr. Coxwell, on coming from the ring, noticed that the centre of the aneroid barometer, its blue hand, and a rope attached to the car were all in the same straight line, and this gave a reading of seven inches and leads to the same result. Therefore, these independent means all lead to about the same elevation, viz. fully seven miles."

Mr. Glaisher's circumstantial evidence of the height he reached has been assailed lately, partly from his assumption that the velocity of the balloon while rising and falling during the thirteen minutes was uniform, but principally from the supposition that men could have survived in that region of death, without at least artificial means of respiration. While it is certain that Berson's observations, which are described later, were made at a greater height than Glaisher's, yet all credit must be given to this Nestor of aeronautical and meteorological science in Great Britain, who is still living at the advanced age of ninety.

The example of Glaisher was not followed in England, but it stimulated interest in the balloon again in France, where MM. Flammarion, de Fonvielle, and Tissandier have made many ascents for scientific purposes, and have presented the results in a popular form to the public. Photography in a balloon is generally a failure on account of the intense reflection from the upper cloud surfaces and the haze which masks the earth. Consequently, for scenic effects we must rely upon sketches, of which those in that interesting, but now rather rare book, _Travels in the Air_, may be referred to. The high atmosphere is often filled with fine ice crystals which, though invisible from below, occasion curious optical phenomena, and some of these have been sketched by M. Albert Tissandier, who has the advantage of being an artist as well as an aeronaut.

Of the many narratives of balloon voyages, one of the most thrilling is the tragedy of the _Zenith_. In 1875, through the co-operation of the French Academy of Sciences and other scientific bodies, it was arranged to make two voyages, one of long duration, the other to a great height, in the balloon _Zenith_. The long voyage from Paris to Bordeaux was successfully accomplished in twenty-four hours, and on April 15 the _Zenith_ again rose from Paris, carrying MM. Gaston Tissandier and CrocÈ-Spinelli, with Sivel as aeronaut. By the advice of M. Paul Bert, the distinguished physiologist, three small balloons of oxygen were provided to assist respiration. The scientific apparatus was as follows: a pump was arranged to draw air through tubes filled with potash in which to store the carbonic acid at different heights in the atmosphere, in order that analysis might determine if its proportion diminished at great heights; a spectroscope was employed to examine the line of water-vapour in the atmosphere, and two aneroid barometers were provided, one giving the pressure corresponding to heights up to 13,000 feet, the other the pressure between 13,000 and 30,000 feet. There were also two barometric tubes registering the lowest pressure, as well as thermometers and other scientific instruments. At 15,000 feet the voyagers began to breathe oxygen, which had been used beneficially by Sivel and CrocÈ-Spinelli in a high ascent the previous year. At 24,000 feet Tissandier wrote in his notes: "My hands are freezing. I am well. We are all right. Haze on horizon with small rounded cirrus. We are rising. CrocÈ pants. We breathe oxygen. Sivel shuts his eyes, CrocÈ does the same." Five minutes later: "Sivel throws out ballast, temperature -11∞ Cent., barometer 300 millimeters." After this, Tissandier became so weak that he could not turn his head to look at his companions. He tried to seize the oxygen tube, but was unable to move his arms. His mind was clear, and he saw the barometer sink below 280 millimeters, indicating a height of 27,000 feet. Then he fainted. After a half-hour of unconsciousness he revived and wrote: "We are falling, temperature -8∞, barometer 315 millimeters. I discharge ballast. CrocÈ and Sivel unconscious in bottom of basket. We fall rapidly." Again he fell into a stupor, from which he was roused by CrocÈ shaking his arm, saying, "Throw out ballast!" which he did, together with the pump, wraps, etc. What happened after this is unknown, but probably the balloon, thus lightened and the gas in it being warm, rose again nearly as high as before. When Tissandier came to his senses the balloon was falling with frightful speed, and in the bottom of the basket, which was oscillating violently from side to side, were crouched his two companions with black faces and bloody mouths. The shock of striking the ground was terrific, but the anchor held, and the balloon soon emptied. From the barometric data it appears probable that the _Zenith_ attained twice a height of about 28,000 feet, and that asphyxiation from the long deprivation of sufficient oxygen killed the two companions of Tissandier and nearly proved fatal to him.

This disaster discouraged further attempts to reach high altitudes, and with the exception of the ascent to 23,000 feet in France by MM. Jovis and Mallet, no more were made until the past decade. The results of the meteorological observations were seen to be strangely discordant; for example, the temperature of 40∞ below zero, observed by Barral and Bixio at a height of 23,000 feet, and 80∞ above zero, noted by the American aeronaut Wise, at 6000 feet. The prophecy "that the balloon-basket would be the cradle of the young science of meteorology" seemed unlikely to be realized, but, nevertheless, observations in balloons continued to be made in France, Italy, and Russia. In the United States a series of balloon ascents was conducted by the Signal Service, which then included the Weather Bureau, and the height of 15,500 feet reached by Professor Hazen in 1887 is probably the greatest at which observations in the free air have been made in America.

The difficulty of obtaining the true temperature of the air from a balloon is great, and without special precautions the observations give the conditions of the free air even less well than do observations on mountain summits. During a rapid ascent the air is carried up in the balloon basket like water in a well-bucket, and since the balloon drifts with the wind it is relatively in a calm, so that there is no circulation of air; the thermometers, even when screened from direct sunshine, are affected by radiation from the heated gas-bag above, and moreover they are not sufficiently sensitive to follow the changing temperature of the air strata so quickly traversed by the balloon. The aneroid barometer, from which the height of the balloon is calculated, cannot respond to rapid changes of pressure; consequently there is a double source of error in determining the height at which the temperature is measured. Ordinarily, the temperature of the air may be obtained quite accurately by slinging in a circle a thermometer attached to a cord, even though this is done in sunshine. During two balloon ascents by the writer, a sling thermometer was found in extreme cases to read 14∞ lower than was recorded by automatic instruments, hung in their usual position from the ring of the balloon. The sling thermometer, however, is influenced by intense insolation, and moreover cannot be swung far enough outside the basket of a balloon to insure good results. The standard instrument for obtaining the temperature of the air under all conditions, adopted for international use in 1898, is a modification of that used by Welsh forty-five years before. This instrument, which is the invention of Dr. Assmann of Berlin, is called the aspiration thermometer, and is designed to prevent the casing surrounding the thermometer from being heated by insolation or conduction, and to insure a flow of air past the thermometer bulbs.

The reorganization of balloon observations was accomplished by the German Society for the Promotion of AÎrial Navigation, which has been assisted by the Prussian Meteorological Institute, and by officers of the German Army Balloon Corps. The German Emperor takes a personal interest in the work, and has aided it by the gift of a considerable sum of money. The first voyage under the direction of the Society was made in 1888, and many notable ones followed. In 1891, through the courtesy of the president, Dr. Assmann, the writer made an ascent from Berlin in a balloon equipped for accurate observations, with the special purpose of comparing the sling with the aspiration thermometer. The car of the balloon is shown in Fig. 3. A companion was the now famous Dr. Berson, who then made his second ascent, but who has now become an expert aeronaut by reason of more than fifty ascensions, some of them to great heights. On December 4, 1894, he ascended alone from Stassfurt, Prussia, in the _Phoenix_, to probably the greatest height ever reached by man, at least in a conscious state. By breathing oxygen he was able to keep his senses and to read the barometer at 9∑1 inches, indicating approximately an altitude of 30,000 feet, and the aspirated thermometer at 54∞ below zero. An ordinary thermometer read 11∞ below zero in the sun, showing its heat was much diminished in consequence of the haze that prevailed even at this enormous height. The cirriform clouds which surrounded the balloon were found to have the structure of snow-flakes rather than that of ice-crystals. The chief result of this record-breaking ascent was the extraordinarily low temperatures recorded at great heights, as compared with those observed by Glaisher, Tissandier, and others. An inversion of temperature--that is an increase of temperature with height--prevailed up to a mile, but above that the temperature fell at a rapid and accelerated rate which approached the adiabatic fall above 26,000 feet. The wind, which was almost calm at the earth's surface, increased to a gale in the high atmosphere, and carried the balloon along at an average speed of thirty-six miles an hour. Wishing to demonstrate conclusively whether the insular position of England influenced the temperature of the high atmosphere, as had been suggested, Dr. Berson determined to execute a high ascension in England during the prevalence of a barometric maximum in summer, when the air column would be abnormally warmed and the upper isothermal surfaces elevated. An opportunity was afforded Berson to follow in Glaisher's footsteps on September 14, 1898, when abnormal heat prevailed in Europe. Berson, with the aeronaut Spencer, in the balloon _Excelsior_, rose from the Crystal Palace in London to the height of 27,300 feet, where he observed a temperature of -29∞. The oxygen inhaled prevented harmful physiological effects except for the discomfort caused by the enormous reduction of temperature from 80∞ at the ground only thirty-five minutes before. The temperature decreased rapidly at first, then moderately up to three miles, and above that it fell almost at the adiabatic rate. Even in this hot summer maximum of pressure and notwithstanding the maritime climate and south-westerly currents, a temperature about 29∞ below zero reigned at 27,000 feet, being only a few degrees warmer than Berson had observed in winter at the same height above Germany. Yet Glaisher, in all his ascents, two of which exceeded 26,000 feet, never recorded a temperature of less than 5∞ below zero. These relatively high temperatures, obtained also by Welsh, Tissandier, and Gay-Lussac, must be attributed to the insufficient protection of the thermometers against insolation, to the proximity of the instruments to the heated basket and its occupants, and lastly, to the sluggishness of the thermometers themselves, from lack of ventilation, during the rapid passage through air-strata of different temperatures. Plate VI. indicates the change of temperature with height observed during the four highest balloon ascents in Europe and in the United States. Dots indicate the observations while ascending, and crosses the observations while descending; these are connected by full and broken lines respectively, an inclination upward to the left showing a decrease of temperature with height and _vice vers‚_. The adiabatic lines, representing a fall of temperature of 1∞ Fahrenheit per 183 feet of ascent, serve for comparison.

This account of notable balloon ascents should not be closed without mentioning the most daring and unique of all, the voyage of Mr. S. A. AndrÈe towards the north pole in 1897. Although his was a voyage of geographical discovery, and not one for the exploration of the air, yet meteorological and other observations were to be made, and AndrÈe had familiarized himself with the instruments and the management of a balloon during several voyages in Sweden. The success of the polar voyage depended primarily upon the prevalence of southerly winds, and the ability of the balloon to keep afloat long enough to profit by them, even should they be light and variable at times. Therefore the impermeability of the balloon to hydrogen gas was of vital importance, and it was the conviction that the _Eagle_, of 140,000 cubic feet, was neither sufficiently large nor staunch to sustain itself for thirty days, the time which might be required to reach Behring Straits, that led Dr. Nils Ekholm, the meteorologist and physicist, to withdraw from the expedition. Unfortunately, his fears seem to have been well founded, and it is probable that we must now abandon hope of the safety of the brave AndrÈe and his two companions.

A less perilous voyage northward across the Alps was attempted in 1898 by Professor Heim, the Swiss geologist, and two associates, conducted by the Italian aeronaut, Spelterini. With an automatic photographic camera, similar to one described in the next chapter, it was hoped to get views of the high Alps from above, which would be alike valuable for geologic and topographic study. Extensive meteorological observations were made in connection with the sixth international balloon ascent, but only the Jura was crossed, at an altitude of 13,000 feet, because the balloon travelled in a north-westerly direction, instead of north-east as was expected.

Many years ago Wise and Donaldson, the American aeronauts, proposed to cross the Atlantic Ocean in a balloon. The difficulties which present themselves in such an undertaking are purely technical, and given a balloon which loses its gas so slowly that its buoyancy can be maintained for several days, there seems to be no reason why such a balloon, at a height of four or five miles, could not pass from San Francisco to New York, or from the United States to Europe, since the motion of the upper clouds proves that the high atmosphere moves almost constantly with great velocity from the west to the east. The dirigible balloon has not been realized except in nearly calm weather, but the aeronaut can often reverse his direction by ascending or descending into a contrary wind to that in which he has been travelling. Frequently no clouds separate these opposing currents, which become apparent only when a balloon enters them.

It has been mentioned that in 1869 Glaisher made observations in a captive balloon in England up to the height of 1700 feet in order to study the conditions of the air within this distance of the earth, which could not be done in a free and rapidly moving balloon. Although captive balloons are frequently used in the European cities to lift people who wish to enjoy the view from a height of 500 or 1000 feet, they appear to have been little used by scientific observers since the time of Glaisher. In 1890-91 the aeronautical society at Berlin employed a captive balloon in connection with the observations in free balloons which have been described. This captive balloon had a capacity of only 5000 cubic feet, but it sufficed to lift an apparatus weighing sixteen pounds, designed by Dr. Assmann to record atmospheric pressure, as well as the temperature and relative humidity of the air. The balloon, attached to a cable 2600 feet long, was drawn down by a steam engine. It was possible in this way to have simultaneous observations at three levels, viz. near the ground, in the free air at a height of about half-a-mile, and at the highest level attained by a free balloon. But the captive balloon is often at a disadvantage, for the wind drives it down, and although the meteorograph mentioned had ingenious devices to neutralize the violent shocks caused by this and by the rebound of the balloon after the gust of wind, yet these impaired the automatic record. The height to which the balloon rose was so much diminished by the wind that instead of 2600 feet, which the balloon attained in calm weather when the cable was vertical, the average height of the twenty-four ascents was but half this, and in very windy weather the balloon could not rise at all.

To obviate these difficulties, a few years ago there was invented by two officers of the German army, Lieutenants von Siegsfeld and von Parseval, a captive balloon capable of resisting strong winds, called, from its action as a kite, the _Drachen-Ballon_ or kite-balloon, and which at the present time is being successfully used in the German Army and Navy for reconnoitring in all kinds of weather. A smaller kite-balloon, of 7700 cubic feet capacity, filled either with hydrogen or with illuminating gas, was first used to lift meteorological instruments at Strassburg in 1898, where it remained at a height of several hundred feet during twenty-four hours. As is seen from Fig. 4, the balloon is cylindrical, with hemispherical ends, and is attached to its cable like a kite, so that the wind acts to lift and not to depress it. The cylinder is divided by a diaphragm near its lower end into two chambers, the upper and larger one being filled with gas, while the lower chamber, by means of a valve opening inwards, receives the pressure of the wind which presses against the diaphragm, and preserves the sausage-like form of the balloon in spite of leakage of gas. Another wind-bag encircling the bottom of the air-chamber serves as a rudder, and lateral fins or wings give stability to the balloon about its longer axis. The instruments are placed in a basket hung far below the balloon. In cases where there is little or no wind at the ground, captive balloons can render valuable service for meteorological observations, but in all other cases kites are preferable. The reasons for this assertion will be given when we consider kites.

From what has been said it will be perceived how much the Germans did to advance scientific ballooning, yet their constant rivals, the French, found a way to surpass them in the exploration of the atmosphere. For several years the struggle for supremacy in the attainment of the greatest heights was keen between the scientific men of both countries, but a truce was declared at Paris in 1896, and since then both nations have worked together harmoniously. The friendly meeting of French and German physicists at Strassburg in 1898 to agree upon the details of co-operation, typified the union of nations through science, and while it is true that the atmosphere has no boundaries and cannot be pre-empted, let us hope that the common aims of science will ultimately obliterate even political boundaries.