Page:The American Cyclopædia (1879) Volume I.djvu/168

 148 AERONAUTICS moving in opposite directions, to which they are obliged to trust themselves, if desirous of travelling in a horizontal direction. M. Flam- marion made the curious discovery that the traces of his various voyages are all represented by lines tending to curve in one and the same general direction; whence he concluded that above the soil of France the currents of the atmosphere are constantly deviated circularly, and in a south-west-north-east-south direction. Still more curious was the discovery by Mr. Glai- sher of what may be called an aerial gulf stream. In his ascent of Jan. 12, 1864, he reached a warm current at a height of 1,300 feet. At 3,000 feet the temperature was 45, being 3 warmer than at the surface, and for the next 3,000 feet it was higher than on the earth. It then gradually fell to 11 at 11,500 feet. This warm stratum of atmosphere was a current moving from the S. W. in the direction of the gulf stream. Fine granular snow was falling into it. The existence of this warm S. W. current goes far, Mr. Glaisher thinks, to ex- plain why England possesses a winter temper- ature so much higher than her latitude would indicate. The same observer found that the time of the vibration of a magnet was greater than on the earth ; that the number of pulsa- tions and inspirations increased considerably at the higher elevations, although the same indi- viduals were differently affected at different times ; that the velocity of the wind was much preater at a high elevation than near the sur- face; and that sounds from the earth were more or less audible according to the amount of moisture in the air. When in the clouds at 4 m. high he heard a railway train ; but when clouds were below, no sound ever reach- ed the ear at this elevation. The barking of a little dog was heard at the height of 2 m., while a multitude of people shouting was not heard at 4,000 feet. At the greatest heights to which Mr. Glaisher ascended he found that the color of the unclouded sky deepened to an intense prussian blue when the air was free from moisture. He rejects the theory which ascribes this to reflection from vesicles of water, and concludes that it must be caused by reflection from the air, whose polar- izing angle is 45. Soon after the invention of balloons the idea was entertained that they might be used to advantage in war for pur- poses of observation and reconnoissance. An aerostatic school was established at Meudon in France, and a number of balloons were dis- tributed among the French army. At the sieges of Maubeuge, Charleroi, Mannheim, and Ehrenbreitstein they proved to be of some value. It is said that the battle of Fleurus was gained by Gen. Jourdan in 1794 mainly through information of the Austrian positions and movements communicated by French officers stationed in a balloon. The machine was held by a cable, but its tether was easily extended by means of a windlass, so that the observers could soar above the enemy's fire. This is the last we hear for many years of the use of balloons in warfare. In the Italian cam- paign of 1859 they were again employed by the French, and one is reported to have aided them effectually at the battle of Solferino. Early in the American civil war (1861-'5) a balloon corps was organized by the United States war department, in the management of which Messrs. La Mountain, Lowe, and other experienced aeronauts were associated. Mr. Lowe first performed the feat of telegraphing from an aerial station 600 feet above the earth. In the summer and autumn of 1861 many bal- loon reconnoissances were made along the Po- tomac and in the neighborhood of Fortress Monroe. The balloon corps formed a part of Gen. McClellan's expedition to the peninsula in the spring of 1862, and when his army in May and June occupied the lines in front of Richmond, the balloons were brought into daily use for purposes of observation. On one occasion, while Gen. Fitz-John Porter was watching the movements of the enemy from a captive balloon, the cable broke, and he waa carried over the confederate lines. By pulling the valve string he caused the machine to de- scend, when it struck a current of air going in the opposite direction, and he landed safely within the Union lines. During the two days of the battle of Fair Oaks Mr. Lowe watched the conflict from an elevation of 2,000 feet, and was the first to announce the enemy's retreat to Richmond. After the retreat of McClellan to Harrison's Landing the balloon corps seems to have been disbanded, and no subsequent employment of the balloon for military purposes is recorded during the war. At the commencement of the Franco-Prussian war of 1870-'7l a proposal was made to Marshal Lebceuf that the French army should be supplied with balloons, but he rejected it. A similar proposal was made to the German war department, which was accepted, but failed because the balloons were placed in un- skilful hands. The siege of Paris by the Ger- mans in 1870-'71 gave a new and unexpected impulse to the science of aerostatics. Toward the close of September, 1870, the city was com- pletely invested, and the balloon, rejected by the French government as of no practical use a few months previous, was gladly employed by the besieged as a means of communicating with those parts of the country not under the con- trol of the enemy. As no machine in the city was at that time considered sufficiently trust- worthy to pass over the besieging lines in safe- ty, balloon factories were established in two of the principal railway stations, which pre- vious to the capitulation turned out nearly 70 machines. The material of the envelope was calico varnished on the exterior with a mix- ture of linseed oil and oxide of lead, and the network, car, and other appurtenances were of the customary pattern. The balloons were of an average capacity of 70,000 cubic feet. The first left Paris Sept. 23 with 227 pounds