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 9¾ 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 Crocé-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 Crocé-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. Crocé pants. We breathe oxygen. Sivel shuts his eyes, Crocé 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. Crocé and Sivel unconscious in bottom of basket. We fall rapidly." Again he fell into a stupor, from which he was roused by Crocé 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.
