Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/217

Rh ASCENTS.] AERONAUTICS 199 1862-66. It appeared as one of th results of the ex periments 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 vhich 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, cirrus 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 investiga tions, 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 accu rately 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 lunger 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 currents 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 cur rents 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. &quot;With regard to physiological ob servations, Mr Glaisher 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, abcut 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 in sensible. 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 the 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 public 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 troublesome 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 gas re quired 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, although, in the absence of instruments, it is not unusual for the aeronaut to ex aggerate 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 certainty. A quc.ntity 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 Ascents or nine ascents from Paris for scientific purposes. The w - f lai1 heights reached were not great, but the general result of ? a _^ t the observations was to confirm those made by Mr Glaisher. See M. Flammarion in Voyages Aeriens, 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. The balloon had not been discovered very long before it Use of 1 received a military status, and soon after the commence- lo p^ s f ment of the French revolutionary war an aeronautic school mi was founded at Meudon ; Guyton de Morveau, the chemist, &quot; and Colonel Coutelle being the persons in charge. Four balloons were constructed for the armies of the north, of the Sambre and Meuse, of the Rhine and Moselle, and of Egypt. In June 1794 Coutelle ascended with the .adju tant and general to reconnoitre the hostile army just before Reconnr the battle of Fleurus, and two reconnaissances were made, sauces I each occupying four hours. It is generally stated that it f re the was to the information so gained that the French victory was due. The balloon corps was in constant requisition during the campaign, but it does not appear that, with the exception of the reconnaissances just mentioned, any great advantages resulted, except in a moral point of view. But even this was of importance, as the enemy were much dis concerted at having their movements so completely watched, while the French were correspondingly elated at the supe rior information it was believed they were gaining. An attempt was made to revive the use of balloons in the African campaign of 1830, but no opportunity occurred in which they could be employed. It is said that in 1849 a reconnoitring balloon was sent up from before Venice, and that the Russians used one at Sebastopol. In the French campaign against Italy in 1859 the French had recourse to the use of balloons, but this time there was not any aerostatic corps, and their management was entrusted to the brothers Godard. Several reconnaissances were made, and one of especial interest the day before the battle At Sol- of Solferino. Xo information of much importance seems, ferill - however, to have been gained thereby. The Fleurus re-