be had recourse to, or even entered, except in the extreme | necessity of the state. Under the emperors the senate continued to have at least the nominal management of the cerarium, while the emperor had a separate exchequer, called the fiscus. But after a time, as the power of the emperors increased and their jurisdiction extended till the senate existed but in form and name, this distinction virtually ceased. Besides creating the fiscus, Augustus also established a military treasury (ærarium militare), containing all moneys raised for and appropriated to the maintenance of the army. The later emperors had a separate ærarium privatum, containing the monies allotted for their own use, distinct from the fiscus, which they administered in the interests of the empire.

AERATED WATERS. Waters impregnated with an unusually large proportion of carbonic acid, or other gaseous substances, occur abundantly in springs throughout the world; and, in addition to their gaseous constituents, generally hold in solution a large percentage of different salts. The manufacture of aerated waters arose out of the attempt to imitate these by artificial means, but till about the beginning of the present century such efforts did not meet with great success. The earliest method of producing acidulated water was that which still obtains in the preparation of effervescing draughts, such as are made from "Seidlitz" powders. These powders consist of separate portions of sodium bicarbonate and tartaric acid, which, on being dissolved together in water, form sodium tartrate and liberate carbonic acid, which bubbles up through the water. In recent years "granular" effervescent preparations have been introduced, in which the acid and salt are mixed in a dry state, and produce their reaction on being dissolved. The popular preparation termed effervescent citrate of magnesia, and several others under a variety of names, consist essentially of sodium bicarbonate and tartaric acid, to which a little citric acid is sometimes added. A limit, however, is set to the use of waters so aerated on account of the purgative action of the alkaline earths they necessarily contain.

In the manufacture of common aerated waters the carbonic acid is prepared apart from the pure water in which it is to be dissolved. There are essentially only two methods on which the manufacture is conducted, although there is an endless variety in the apparatus used. In the first process, which may be distinguished as the method of chemical pressure, the carbonic acid gas saturates the water by its own pressure, passing directly from the chamber in which it is produced and purified into the cylinder or cylinders containing the water to be aerated. The small apparatus frequently used in private houses and hospitals may be taken as an illustration of this method. The most common form consists of two strong glass globes A and B, protected by netting in case of breakage. Into the globe A are placed the materials for generating carbonic acid, usually in this case tartaric acid and sodium bicarbonate. When charged with these materials, a metal tube C, accurately fitted to the aperture in the globe, is inserted. The globe B is inverted and filled with water, and in this position the globe A is screwed tightly up by the joint D, the metal tube reaching to near the top of globe B. On placing the apparatus upright, a proportion of water escapes through the metal tube into globe A, acts on the charge it con

D

B

tains, and evolves carbonic acid, which passes up the tube and saturates the water in B. As the pressure of the gas

augments, the quantity absorbed increases, and when fu.ly saturated the aerated water may be drawn off by the cock E. In manufacturing on a large scale, a combination of globes or cylinders is used for producing continuous action, and less expensive sources of carbonic acid than sodium bicarbonate and tartaric acid are employed. The second or mechanical pressure process is that generally followed in the manufacture in this country. In this process the gas is prepared in a lead chamber by the action of sulphuric acid on chalk, and is washed by passing through water into the gas-holder in which it is collected. By the action of a force-pump, water, filtered when necessary, and carbonic acid, are pressed, in due proportions, into a very strong copper cylinder, tinned internally, termed a receiver or saturator, in which an agitator is kept revolving. A pressure gauge is attached to the receiver, and when the index indicates from 120 to 140 b pressure per square inch, what is termed aerated water, and very frequently does duty for sodawater, is ready for drawing off at the bottling apparatus. Real soda-water is best prepared by adding to the water before aeration a proportion of sodium bicarbonate equal to about 30 or 36 grains per pint of water. Potash-water, Seltzer, lithia, Carrara, bromide of potassium, and a host of other waters, are similarly prepared, the various salts being used in different proportions, according to the taste and experience of manufacturers. Lemonade, and other aerated drinks flavoured with fruit syrups, have the proportion of syrup placed in the bottle to which simple aerated water taken from a receiver, indicating a pressure of 80 to 100 b per square inch, is added. From a syrup composed of 14 lb of sugar, 2 oz. of tartaric acid, 3 oz. of citric acid, and 4 drachms of essence of lemon, dissolved in 2 gallons of water, 30 dozen bottles of an excellent quality of lemonade can be prepared. On account of the rapidity with which the gas escapes on the removal of pressure, special arrangements are required for the bottling and corking processes, and the frequent explosion of bottles necessitates guards to protect the bottler. A dexterous bottler will fill and cork 5000 bottles in ten hours. The consumption of aerated waters, especially in hot climates, is very great.

AEROE, or ARROE, an island of Denmark, in the Little Belt, lying 7 miles S. of Funen, between Alsen and Langeland. It is of an irregular triangular shape, about 15 miles long and 8 broad at the widest points, with a hilly surface, but a fertile and well-cultivated soil. Population, 10,200; chief town, Aeroeskjobing, on the east coast."

AEROLITE (anp, air, and Xíos, a stone), a stony or metallic body, which, falling through the atmosphere, reaches the earth's surface. These meteoric stones generally contain a considerable proportion of iron; indeed, the iron in some of these substances exceeds the siliceous matter, and some have then given them the name of meteoric irons. A remarkable aerolite that fell at Ægospotami, in 467 B.C., was, according to Pliny, to be seen in his day, and was then as large as a waggon. In 1492 one fell at Ensisheim, in Alsace, that weighed 270 b.; and, not to mention others, one of 12 b weight is reported to have fallen in California in August 1873, which penetrated the earth to the depth of 8 feet, and when dug up was so hot that it could not be handled. Aerolites often reach the earth in groups or showers, as at L'Aigle, in Normandy, in 1803; at New Concord, Ohio, in May 1860; and at Dhurmsala, in the Punjaub, in July the same year. The area on which a shower of aerolites falls is usually elliptical, the largest stones being near one end of the ellipse, the major axis of which extends in some cases to a length of eighteen or twenty miles. See METEOR.

185

Gradual discovery of naviga

tion.

Analogy

between

and flying only very vague.

IN

AERONAUTICS

N every stage of society men have sought, by the combi- |
nation of superior skill and ingenuity, to attain those
distinct and obvious advantages which nature has conferred
on the different tribes of animals, by endowing them with a
peculiar structure and a peculiar force of organs. The
rudest savage learns from his very infancy to imitate the
swimming of a fish, and plays on the surface of the water
with agility and perseverance.
But an art so confined in
its exercise, and requiring such a degree of bodily exertion,
could not be considered of much avail. It must have been
soon perceived (even if the discoveries of the arts of nata-
tion and navigation were not absolutely simultaneous), that
the fatigue of impulsion through the water could be greatly
diminished by the support and floating of some light sub-
stance. The trunk of a tree would bear its rude proprietor
along the stream; or, hollowed out into a canoe and fur-
nished with paddles, it might enable him even to traverse
a river. From this simple fabric the step was not great
to the construction of a boat or barge, impelled by the
force of oars. But it was a great advance to fix masts and
apply sails to the vessel, and thus substitute the power of
wind for that of human labour. The adventurous sailor,
instead of plying on the narrow seas or creeping timidly
along the shore, could now launch with confidence into the
wide ocean. Navigation, in its most cultivated form, may
be fairly regarded as one of the sublimest triumphs of
human genius, industry, courage, and perseverance.

Having by his skill achieved the conquest of the waters that encompass the habitable globe, it was natural for man navigation to desire likewise the mastery of the air in which we breathe. In all ages, therefore, great ingenuity has been expended in efforts at flying, all of which have as yet resulted in failure. But the analogy between sailing on the water and sailing in the air is not so close as many enthusiasts have supposed it to be. There is a general resemblance, inasmuch as in both cases the propulsion must be made by means of a fluid. But in the one case the fluid is inelastic, in the other clastic; and the physicist or mathematician knows how vastly different are the properties of liquids, even in fundamental points, from those of aeriform or gaseous bodies. Again, in the one case the vessel floats on the surface of the water, in the other it must float totally immersed in the aerial fluid. A ship, while sailing, is acted on by two fluids-the water supports it and the air propels it; but a ship sailing in the air would be only under the action of the one fluid that surrounds it on all sides. These few considerations-and many more might be added-indicate the essential distinctions between the two cases; and a very little thought shows that it is not so remarkable as it at first sight appears, that the invention of the art of sailing on the water should be lost in prehistoric antiquity, while that of sailing in the air is not a century old; and that while navigation is one of the most perfect of the arts, the power of directing a body floating in the air still remains unattained. Many have argued, Many have argued, that because navigation is an accomplished fact, therefore the navigation of the air must be possible; and without denying the truth of the conclusion, it is worth while at the outset of this article to point out the fallacy of the reasoning. It is true that there is no reason to despair of the attainment of aerial navigation, as the history of invention and science records many victories as great and at one time apparently as far off; still, it is as well to notice how little assistance the old discovery affords towards the solution of the new: it may, indeed, even be that progress has been retarded by the false analogy, for we may feel pretty certain

and

that if ever the air is navigated, it will be by ships pre-
senting little resemblance to those that traverse the ocean.
The subject of aerostation is scarcely ever alluded to by Aerostatic
the classical writers, and the fable of Daedalus and Icarus, attempts of
the Greeks
and the dove of Archytas, form almost all we have to re-
cord in relation to flying previous to the dark ages. Dæ- Romans.
dalus, an Athenian, killed his nephew Talus through Daedalus
jealousy of his talents, and fled with his son Icarus to Crete, and Icarus.
where he built the celebrated labyrinth for Minos, the
king. But having offended Minos, so that he was im-
prisoned by him, he made wings of feathers, cemented with
wax, for himself and his son, so that they might escape by
flight. He gave his son directions to fly neither too low
nor too high, but to follow him. Icarus, however, be-
coming excited, forgot his father's advice, and rose so high
that the heat of the sun melted the wax of his wings, and
he fell into the sea near Samos, the island of Icaria and
the Icarian sea being named after him. Dædalus accom-
plished his flight in safety. (Ovid, Met. lib. viii. Fab. iii.)
The explanation of the myth may be, as has been supposed,
that Daedalus used sails, which, till then, according to
Pausanius and Palæphatus, were unknown, and so was
enabled to escape from Minos' galleys, which were only
provided with oars; and that Icarus was drowned near the
island Icaria. But the whole story of Dædalus is so fan-
ciful a romance, that it is scarcely worth while even to
speculate upon what the infinitesimal fragment of truth that
lay at the bottom of it may have been.

Archytas of Tarentum was a well-known geometer and Archytas. astronomer, and he is apostrophised by Horace (Ode 28, lib. i.) The account of his flying pigeon or dove we owe to Aulus Gellius (Noctes Attica), who says "that it was the model of a dove or a pigeon formed in wood, and so contrived as by a certain mechanical art and power to fly: so nicely was it balanced by weights, and put in motion by hidden and enclosed air." Gellius gives as his authorities "many men of eminence among the Greeks," whom he does not mention by name, and Favorinus the philosopher.

Archytas thus has been regarded as holding to aeronautics much about the same position as Archimedes does to the mechanical sciences; but while the claim of the latter rests on real discoveries and great contributions to knowledge, the former owes his position merely to an unsupported and untrustworthy tradition. When the fire-balloon was invented, it was only natural that many should see in the "hidden and enclosed air" of Archytas' dove a previous discovery of the hot-air balloon. It is quite possible that Archytas may have rarefied the air in his dove by heat, and so made it ascend; but in this case it certainly could not have been made of wood. But if the dove ever was made to appear to fly, it is much the more probable that this effect was produced, as in the scenes at theatres, by means of fine strings or wires invisible to the spectators.

The ancients seem to have been convinced of the impossibility of men being able to fly, and they appear to have made no attempts in this direction at all. The power of flying was attributed only to the most powerful of the divinities; and it was regarded as only secondary to Jupiter's prerogative of flashing the lightning and hurling the thunderbolt.

The history of aerostatics in the Middle Ages, like that of Aerostatics every other subject relating even remotely to science or in the dark knowledge of any kind, is little better than a record of the ages. falsehoods or chimeras circulated by impostors or enthu siasts. Truth was completely obscured by ignorance and fanaticism, and every person of superior talents and acquire

Attempts at flying.

ments was believed to deal in magic, and to perform his | such narrations, in some of which the experimenter is
feats of skill chiefly through the secret aid granted him by
the prince of darkness; and in a later and comparatively
recent period, those wretched creatures whom the unfeeling
credulity of our ancestors, particularly during the prevalence
of religious fanaticism, stigmatised and murdered under
the denomination of witches, were supposed to work all
their enchantments, to change their shapes at will, and to
transport themselves through the air with the swiftness of
thought, by a power derived from their infernal master, to
whom was thus assigned the privilege of conferring the gift
of aerial navigation upon his servants.