1902 Encyclopedia > Aeronautics > Results of Experiments Conducted During Mr James Glaisher's Balloon Ascents. Ascents of Flammarion, 1867-68.

Aeronautics
(Part 36)




Results of Experiments Conducted During Mr James Glaisher's Balloon Ascents. Ascents of Flammarion, 1867-68.

It has been found necessary in the present notice to allude merely to the more striking points noticed in Mr. Glaisher's twenty-eight ascents. The number of observations made by him was of course great, and it is only necessary here to repeat that they are to be found in the Report of the British Association for the Advancement of Science 1862-66. It appeared as one of the results of the experiments that the rate of the decline of temperature with elevation near the earth was very different when the sky was clear from what was the case when it was cloudy; and the equality of temperature at sunset and increase with height after sunset were very remarkable facts which were not anticipated, and which have an important bearing on the theory of refraction, as astronomical observations are usually made at night. Even at the height of 5 miles, circus clouds were seen high in the air, apparently as far above as they seem when viewed from the earth, and the air must there be so exceedingly dry that it is hard to believe that their presence can be due to moisture at all. The results of the observations differed very much, and no doubt the atmospheric conditions depended not only on the time of day, but also on the season of the year, and were such that a vast number of ascents would be requisite to determine the true laws with anything approaching to certainty and completeness. It is also clear that England is a most unfit country for the pursuit of such investigations, as, from whatever place the balloon started, it was never safe to be more than an hour above the clouds for fear of reaching the sea. It appeared from the observations that an aneroid barometer could be trusted to read as accurately as a mercurial barometer to the heights reached. The time of vibration of a horizontal magnet was taken in very many of the ascents, and the results of ten different sets of observations proved undoubtedly that the time of vibration was longer than on the earth. In almost all the ascents the balloon was under the influence of currents of air in different directions. The thickness of these currents was found to vary greatly. The direction of the wind on the earth was sometimes that of the whole mass of air up to 20,000 feet, whilst at other times the direction changed within 500 feet of the earth. Sometimes directly opposite current were met with at different heights in the same ascent and three or four streams of air were encountered moving in different directions. Ignoring the different currents of air which caused the balloon to change its direction, and at times to move in entirely opposite directions, and simply taking into account the places of ascent and descent, the distances so measured were always very much greater than the horizontal movement of the air as measured by anemometers. For example, on January 12, 1862, the balloon left Woolwich at 2h. 8m. P.M. and descended at Lakenheath, 70 miles distant from the place of ascent, at 4h. 19m. P.M. At the Greenwich Observatory, by Robinson's anemometer, during this time the motion of the air was 6 miles only. With regard to physiological observations, Mr. Galisher found that the number of pulsations increased with elevation, as also the number of inspirations. The number of his pulsations was generally 76 per minute before starting, about 90 at 10,000 feet 100 at 20,000 feet, and 110 at higher elevations. But a good deal depended on the temperament of the individual. This was also the case in respect to colour; at 10,000 feet the faces of some would be a glowing purple, whilst others would be scarcely affected; at 4 miles high Mr. Glaisher found the pulsations of his heart distinctly audible, and his breathing was very much affected, so that panting was produced by the very slightest exertion; at 29,000 feet he became insensible. In reference to the propagation of sound, it was at all times found that sounds from the earth were more or less audible according to be amount of moisture in the air. When in clouds at 4 miles high, a railway train was heard; but when clouds were far below, no sound ever reached the ear at this elevation. The discharge of a gun was heard at 10,000 feet. The barking of a dog was heard at the height of 2 miles, while the shouting of a multitude of people was not audible at heights exceeding 4000 feet.

The majority of Mr. Glaisher's experiments were made in the summer, partly because ascents took place at this time of the year, and partly because the weather was more settled. But some special ascents were made in the winter; these were found to be very troublecome and costly, owing to the time that was wasted before a suitable day occurred, and to the boisterous weather, which damaged the balloon. Altogether the number of ascents bore but a small ratio to the number of days spent over them. Sometimes it was necessary to wait at Wolverhampton a whole week after the day fixed for the ascent, owing to the unfavourable state of the weather and the necessity of keeping the light has required for the balloon in a separate gasometer (as the lightest gas is the worst in illuminating power), added to the cost and difficulty. When balloons ascend as public exhibitions from places of entertainment it is very rarely that a height of a mile is reached, a although, in the absence of instruments, it is not unusual for the aeronaut to exaggerate the elevation, as the passengers have no reason for disputing what is told them. This must be borne in mind when physiological or other phenomena are described by voyagers unprovided with instruments. We have noticed the observations made in Mr. Glaisher's ascents at greater length, because they are almost the only ones that have been made in which the height and other matters are determined with certainly. A quantity of air was collected in two large bags at the height of 12,000 feet in the ascent on January 12, 1864, and submitted to Professor Tyndall, but he has never made public the analysis of it.

In the years 1867 and 1868 M. Flammarion made eight or nine ascents from Paris for scientific purposes. The heights reached were not great, but the general result of the observations was to confirm those made by Mr. Glaisher. See M. Flammarion in Voyages Aériens, Paris, 1870, or Travels in the Air, London, 1871. Observations were also made in some balloon ascents by M. de Fonvielle, which are noticed in the works just referred to.





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