Page:The American Cyclopædia (1879) Volume I.djvu/165

AEROLITE AERONAUTICS 145 and very often one or more exceedingly violent explosions. It is therefore not surprising that they all present the appearance of having been subjected to great heat. Chemioal analysis has shown that there are two principal kinds, the stony and the metallic aerolites, which by further investigation have been divided into several groups, in accordance with the elements contained and the character of their combina- tions. Stony aerolites resemble the peridot, a universal scoria from the earth's deep interior, underlying the aluminous basic rocks, the granite and gneiss; the latter, being stratified rocks, are never found among aerolites. The specific gravity of stony aerolites is 3'5 to 3 '8, while that of stratified formations, gneiss and granite, and of lava, is only 2-6 to 2 -9. Metal- lic aerolites have a specific gravity of from 6'5 to 8, and consist chiefly of iron, always com- bined with nickel, usually containing 60 per cent, or more of iron and 5 to 25 of nickel, a compound never found on earth ; the other ele- ments are chiefly phosphorus, silicon, alumi- num, cobalt, and manganese. Other substances which have been found in different specimens are: magnesium, titanium, tin, copper, chro- mium, arsenic, calcium, potassium, sodium, sul- phur, carbon, chlorine, nitrogen, and hydrogen in occlusion (see ABSORPTION OF GASES BY SoLr IDS), making 22 elements, one third of those of which the earth is composed. Some aerolites are of a mixed stony and metallic character, but they are never homogeneous; even the metallic ones, which appear to be an alloy, are very heterogeneous. This is manifested by grinding and polishing a face and then acting on it with nitric acid, when some portions will dissolve, and more resistant small crystals will become prominent, showing a decided crystal- line structure. The figures thus formed are called, after their discoverer, Widmanstaett's figures, and they may be made so prominent as to allow the surface to be used as an engraved plate and printed. Our figure represents an aerolite found- in Wisconsin, preserved in the Widmannstaett's Figures. cabinet of I. A. Lapham of Milwaukee, and engraved after the photograph of a section prepared by Dr. J. Lawrence Smith, show- ing the Widmannstaettian figures. The idea suggested by Sir William Thomson before the British association for the advancement of science in 1871, that the existence of vege- 11 VOL. i. 11 table and animal life on our planet may be accounted for by aerolites having brought the first organiaed germs hither, substitutes for the difficult question as to the terrestrial origin of organisms, the still more perplexing one of how they originated on the aerolites. See further Phipson's "Treatise on Meteors, Aerolites, ami Falling Stars " (London, 1866) ; Daubr6e, Rap- port sur les progres de la geologic experimental (Paris, 1867). The latter is very exhaustive, arid contains accounts of experiments in imitating the ^different kinds of aerolites. AEROMETER (Gr. typ, air, and fitrpov, meas- ure), an instrument invented by Dr. Marcus Hunt for ascertaining the mean bulk of gases and the density or rarity of air. It is now little used, and the whole doctrine of air, considered as a fluid, its pressure, elasticity, rarefaction, and condensation, belongs in that department of natural philosophy termed pneumatics. AERONAUTICS (Gr. difc, air, and vavTirig, of or belonging to ships), or Aerostation (Gr. afjp, and oramg, standing), the art of sailing in and navigating the air, and of raising and sustaining substances by means of gases specifically lighter than the atmosphere, contained in a spheroidal bag called a balloon. The former term is the more comprehensive of the two, and includes the whole science of aerial navigation, while the latter is generally confined to ballooning. The myths of Dredalus and Icarus show that the attempts of man to soar above the earth commenced in prehistoric times. Flying ma- chines were expected to effect this object. Archytas of Tarentum is said to have manufac- tured, 400 years B. C., a wooden pigeon which sustained itself in the air a few minutes. Simon Magus, according to Suetonius, met his death in. Rome in the reign of the emperor Nero in an attempt to fly from one house to another. Roger Bacon had some notion of a flying ma- chine to be propelled by a system of wings; and in the latter part of the 15th century Dante, a mathematician of Perugia, rose above Lake Thrasimene by means of artificial wings attached to his body. Many similar attempts have been made since then by persons imper- fectly acquainted with the principles of me- chanical philosophy, which have invariably re- sulted in failure, and the problem is as far from solution as ever. The discovery of the proper- ties of hydrogen gas by Cavendish in 1766 gave the first hint of a practical method of aerial navigation. This is the lightest of the gases, being a little more than 14 times rarer than at- mospheric air; and as early as 1767 Professor Black of Edinburgh announced to his class that a vessel filled with it would naturally rise into the air.. A few years later (1782) Cavallo made a series of experiments on the subject, but did not succeed in raising anything heavier than a soap bubble. The honor of preparing and sending up the first balloon belongs to tho brothers Stephen and Joseph Montgolfier, pa- per manufacturers at Annonay, near Lyons, who, however, at the outset of their experi-