AERATED WATERS.

into use in large cities. In ordinary bread-making, upper division. The powders, consisting of bicarwheat-flour is moistened with water and worked bonate of soda (NaO,HO,2CO,) and tartaric acid (T), into dough, to which common salt and yeast are are then placed in the upper globe by means of the added. The latter causes the flour to ferment or small funnel D, and care is taken, by plugging up decompose, when carbonic acid is given off at every the tube communicating with the lower part by the part; and when the fermented dough is placed in stopper F, that no powder passes into the larger an oven, the bubbles of carbonic acid gas expand, globe. The long tube, C, is then inserted into the and cause the formation of the spongy mass char- globes, and screwed well in. The apparatus is acteristic of good loaf-bread. The process of prepar- inclined till water from the lower globe enters and ing A. B. consists in placing the flour in a strong fills the upper globe about one-third; then it is enclosed iron box, and moistening it with carbonic placed erect, and allowed to be at rest for two hours, acid water, prepared as stated under A. WATERS. when, if the screw stop-cock at the upper part be The dough is then worked up by machinery for opened, the carbonated water will flow out readily ten minutes or so inside the box, from which it is into any vessel placed to receive it. The explanadropped into moulds, which form it into loaves. It tion of the action which goes on in the vessel is, is then placed in an oven, when the carbonic acid, that tartaric acid and bicarbonate of soda have previously introduced with the water within the no action on each other so long as they are dry; dough, expands, and forms a light palatable bread. but whenever water is admitted, the tartaric acid The advantages which this method of working combines with the soda and water to form tartrate bread possesses are-1. There is a saving of the of soda and water (NaO,HO,T), and at the same whole of the waste caused by fermentation, which time, carbonic acid (CO,) is given off, and descendadmits of more bread being made out of a sack of ing the tube into the lower globe, dissolves in the flour than by the old process. 2. The process, water contained therein. Occasionally, bisulphate instead of occupying eight or ten hours, is com- of potash is used instead of the tartaric acid, to save pleted in half an hour. 3. The cost of machinery the greater expense of the latter.-The gazogènes can and gas is less than that of yeast used in the old likewise be used in the preparation of true sodaprocess. 4. The dough requires no handling to water, or Eau de Vichy, by adding a little carknead it, and form it into loaves. 5. The bread bonate of soda to the water in the lower globe before is absolutely pure-it is simply flour, water, and charging with carbonic acid. A. wine may be salt. Finally, should the whole of the bread in obtained by placing white wine with a little sugarthe kingdom be thus made, a very considerable candy in the lower globe instead of water. Sparksaving would be effected in the consumption of ling lemonade is procured when the carbonic acid water is run into a tumbler containing a little sirup of sugar; and A. fruit-beverages, when the water charged with carbonic acid is received in a glass containing about a table-spoonful of either of the fruit-sirups.

flour.

AERATED WATERS are employed largely as refreshing, refrigerant beverages to allay thirst during warm weather, and during feverish conditions of the animal frame. The most common A. beverage is Carbonic acid water, generally spoken of as Soda- The less common A. W., prepared on the large water, though it seldom contains any soda. It is pre-scale, are 1. A. soda-water (true soda-water), obtained pared on the large scale by placing whiting, chalk, by adding 15 grains of crystallised carbonate of or carbonate of lime (CaO,CO,) in a lead vessel soda to each bottle before it is charged with the carbonic acid water; 2. A. potash-water, by employing in a similar way 20 grains of bicarbonate of potash; 3. A. Selters-water, when carbonate of soda and chloride of sodium (common salt) are dissolved in carbonic acid water; 4. A. Carrara-water, when finely divided Carrara marble is dissolved in the acid-charged water; 5. A. lime-water, when other forms of lime than the Carrara marble are used; 6. A. magnesian-water, when magnesia, or the carbonate of magnesia, is used; and A. chalybeate-water, when a compound of iron is dissolved in the carbonic acid water. The latter beverage has lately been employed in medicine, as an easy means of introducing iron into the blood, and with good effect. A. Carrara and lime waters are now administered in cases where the bony structure requires to be strengthened; and A. magnesia-water is a very agreeable mode of giving a patient a dose of magnesia. The well-known effervescing draughts called soda-powders, and seidlitz-powders, are two other kinds of A. drinks. In the former, bicarbonate of soda and tartaric acid are added to water in a tumbler, and a refreshing draught instantaneously prepared. Seidlitz-powders contain tartrate of soda and bicarbonate of soda in one paper, and tartaric acid in the other; and when both are added to water, effervescence ensues, and the liquid is then partaken of.

Gazogène.

B

with water and sulphuric acid (SO), when the sulphuric acid combines with the lime to form stucco or sulphate of lime (CaO,SO,), and carbonic acid (CO) is evolved as gas. The latter is received in a reservoir, and is thereafter forced into water, so that the latter dissolves about five times its own volume of the gas. The water then constitutes a brisk sparkling liquid, with a pungent, but pleasant acidulous taste. On the small scale, and for family use, carbonic acid water may be conveniently prepared in the apparatus known as the gazogène or seltzogène. The complete apparatus is seen at A, and dissected at B and C. In proceeding to use the vessel, the lower globe at B is filled with water by means of the long funnel E, taking care that no water runs into the smaller and

A. W. likewise occur naturally. Water, as it is drawn from a spring, tastes differently from the same water after being boiled and cooled; and this is due to the unboiled water containing the gases oxygen, nitrogen, and carbonic acid-especially the latter-dissolved in it. Spring-water is therefore a natural A. beverage. Rain-water has a mawkish,

AERIAL POISONS-AEROLITES.

insipid taste, mainly because of the minute quantity phers as instances of popular credulity and super-
of gas therein dissolved; but when that rain-water
trickles down the mountain-side, and is dashed
from ledge to ledge of rock, it absorbs and dis-
solves the gases from the air, and is thus naturally
aërated. Many waters are aërated in a natural but
peculiar way, which confers upon them important
medicinal properties; and these will come before us
under their more popular title of Mineral Springs.
AË'RIAL POISONS. See MIASMA.

stition. It was not till the beginning of the 19th c.
that the fact was established beyond a doubt.--
According to Livy, a shower of stones fell on the
Alban Mount, not far from Rome, about 654 B. C.
The fall of a great stone at Egospotami, on the
Hellespont, about 467 B. C., is recorded in the Parian
Chronicle (q. v.), and mentioned by Plutarch and
Pliny. It was still shewn in the days of Pliny
(d. 79 a. D.), who describes it as of the size of a
A. D., a ponderous stone, weighing 260 lbs., fell from
wagon, and of a burned colour. In the year 1492
the sky near the village of Ensisheim, in Alsace;
part of it is still to be seen in the village church.
An extraordinary shower of stones fell near L'Aigle,
in Normandy, on the 26th April 1803. The cele-
brated French philosopher, M. Biot, was deputed by
government to repair to the spot and collect the
authentic facts; and since the date of his report, the
reality of such occurrences has no longer been ques-
tioned. Nearly all the inhabitants of a large district
had seen the cloud, heard the noises, and observed
the stones fall. Within an elliptical area of seven
miles by three, the number of stones that had fallen
could not be less than two or three thousand; the
largest were 17 lbs. in weight. These are only a few
out of hundreds of instances on record.

AERODYNAMICS is that branch of science which treats of air and other gases in motion. It examines first the phenomena of air issuing from a vessel, which correspond in many respects with those of water. See HYDRODYNAMICS. Much depends, as in the case of water, upon the nature of the orifice, whether a mere hole in the side of the vessel, or a tube or adjutage. Another subject of A. is the motion of air in long tubes, where the resistance of friction, &c., has to be ascertained. That resistance is found to be nearly in proportion to the square of the velocity, to the length of the tube, and inversely to its width. A. examines also the velocity of air rushing into a vacuum, of wind, &c. The instrument used for the latter purpose is called an anemometer. See WINDS. Air is found to rush into a void space at the rate of from 1300 to 1400 feet per second. One As was natural with objects of such mysterious of the most important inquiries in A. is the resist-origin, meteoric stones have always been regarded ance offered to a body moving in air, or which is with religious veneration. At Emesa, in Syria, the the same thing the pressure exerted by air in sun was worshipped under the form of a black stone, motion upon a body at rest. The law may be stated, reported to have fallen from heaven. The holy with sufficient accuracy for practical purposes, as Kaaba of Mecca, and the great stone of the pyramid follows: The resistance or pressure is proportional of Cholula, in Mexico, have all the same history. to the square of the velocity. We might conclude from reason, without experiment, that such would be the case; for if one body is moving through the air four times faster than another of the same size, not only will it encounter four times as many particles of air, but it will give each of them four times as great an impulse or shock, and thus encounter 4 x 4, or sixteen times as much resistance.

This resistance is greatly increased by another circumstance, especially with great velocities. The air in front of the moving body becomes accumulated or condensed, and a partial or even entire vacuum is formed behind it. With a velocity of 1700 feet per second, for instance, the resistance is found to be about three times as great as the simple law of the square of the velocity would give. By the operation of these laws of resistance, a heavy body let fall with a parachute attached to it, comes, after a certain time, to move with a velocity approaching more and more nearly to a uniform motion.

A'ËROLITES (Gr. aer, air, and lithos, stone), or METEORIC STONES, FIREBALLS, and SHOOTING-STARS, are now classed together as being merely varieties of the same phenomenon. Aerolites that fall during the day, are observed to be projected from a small dark cloud, accompanied by a noise like thunder, or the firing of cannon; at night, they proceed from a fireball, which splits into fragments with a similar sound. It is believed that the dark cloud that accompanies the fall of aerolites by day, would be luminous at night; and smoking, exploding fireballs have sometimes been seen luminous even in the brightness of tropical daylight. The connection between aërolites and fireballs is thus established. Fireballs, again, cannot be separated from shootingstars, the two phenomena being sometimes blended, and also being found to merge into one another, both with respect to the size of their disks, the emanation of sparks, and the velocities of their motion.

There are numerous records and stories in all ages and countries of the fall of stones from the sky; but until recent times, they were treated by philoso

The existence of such bodies once admitted, led to assigning a meteoric character to strange ferruginous masses found in different countries, and which had no history, or were only adverted to in vague tradition. Of this kind is the immense mass seen by Pallas in Siberia, now in the Imperial Museum at St Petersburg. The largest known is one in Brazil, estimated at 14,000 lbs.

One constant characteristic of meteoric stones is the fused black crust, like varnish, with which the surface is coated. From the circumstance of this coat being very thin, and separated from the inner mass by a sharply defined line, it is thought to indicate some rapid action of heat, which has not had time to penetrate into the substance of the stone. This view is favoured by the fact that the stones are found in a strongly heated, but not incandescent state, when they fall. Their specific gravity ranges from two to seven or even eight times that of water.As to their chemical composition, the predominating element is iron, in a native or metallic state, generally combined with a small proportion of nickel. According to Humboldt, the aerolites that fell in the neighbourhood of Agram, in Croatia, in 1751, the Siberian stone, and specimens brought by that philosopher from Mexico, contain 96 per cent. of iron; while in those of Sienna the iron scarcely amounts to 2 per cent., and, in some rare instances, metallic iron is altogether wanting. A writer in the Quarterly Review, No. CLXXXIII., thus sums up the result of all the chemical analyses hitherto made: We find the actual number of recognised elements discovered in aërolites to be nineteen or twentythat is, about one-third of the whole number of elementary substances (or what we are yet forced to regard as such) discovered on the earth. Further, all these aerolitic elements actually exist in the earth, though never similarly combined there. No new substance has hitherto come to us from without; and the most abundant of our terrestrial metals, iron, is that which is largely predominant in aerolites, forming frequently, as in some of the instances just

AEROLITES.

mentioned, upwards of 90 parts in 100 of the mass. Seven other metals-copper, tin, nickel, cobalt, chrome, manganese, and molybdena-enter variously into the composition of these stones. Cobalt and nickel are the most invariably present; but the proportion of all is trifling compared with that of iron. Further, there have been found in different aerolites, six alkalies and earths-namely, soda, potash, magnesia, lime, silica, and alumina; and, in addition to these, carbon, sulphur, phosphorus, and hydrogen. Finally, oxygen must also be named as a constituent of many aerolites, entering into the composition of several of the substances just mentioned As respects the manner of conjunction of these elements, it is exceedingly various in different

aërolites. A few there are, especially examined by Berzelius and Rose, containing olivine, augite, hornblende, and other earthy minerals; and closely resembling certain crystalline compounds which we find on the surface of the earth.'

Besides those solid masses of considerable size, numerous instances are on record of showers of dust over large tracts of land; and it is remarkable that such dust has generally been found to contain small hard angular grains resembling augite. Stories of the fall of gelatinous masses from the sky are ranked by Humboldt among the mythical fables of meteorology. It has been supposed that such fables may have originated in the very rapid growth of gelatinous algæ, as Nostoc (q. v.).

Fireballs and Shooting-stars. From the height and apparent diameter, the actual diameter of the largest fireballs is estimated by Humboldt to vary from 500 to 2800 feet; others allow a diameter of about a mile. Shooting-stars are thought to have diameters varying from 80 to 120 feet. In most cases of luminous meteors, a train of light many miles in length is left behind. One or two instances are on record where the train of the fireball continued shining for an hour after the body disappeared. The heights of shooting-stars are found to range from 15 to 150 miles, at the points at which they begin and cease to be visible. Their velocities vary from 18 to 36 miles in a second. When it is remembered that the velocity of Mercury in its orbit is 264 miles in a second, of Venus 19-2, and of the Earth 164, we have in this fact a strong confirmation of the planetary nature of meteorites.

swarms are periodic, or recur on the same days of the year. Attention was first directed to this fact on occasion of the prodigious swarm which appeared in North America between the 12th and 13th of November 1833, described by Professor Olmsted of Newhaven. The stars fell on this occasion like flakes of snow, to the number, as was estimated, of 240,000 in the space of nine hours, and varying in size from a moving point or phosphorescent line to globes of the moon's diameter. The most important observation made was, that they all appeared to proceed from the same quarter of the heavens-the vicinity, namely, of the star y, in the constellation Leo; and although that star had changed greatly its height and azimuth during the time that the phenomenon lasted, they continued to issue from the same point. It was afterwards computed by Encke, that this point was the very direction in which the One of the most remarkable facts connected with earth was moving in her orbit at the time. Attenshooting-stars is, that certain appearances of them tion being directed to recorded appearances of the are periodic. On most occasions they are sporadic-same kind, it was observed with surprise that several that is, they appear singly, and traverse the sky in of the most remarkable had occurred on the same all directions. At other times, they appear in day of November, especially that seen by Humboldt swarms of thousands, moving parallel; and these at Cumana in 1799, and by other observers over a

1

AERONAUTICS-AEROSTATIC PRESS.

great extent of the earth. The November stream was again observed in the United States in 1834, between the 13th and 14th, though less intense. Though often vague, and in some years altogether absent, this phenomenon has recurred with such regularity, both in America and Europe, as to establish its periodic character.

Another periodic swarm of considerable regularity is that appearing between the 9th and the 14th of August, and noticed in ancient legends as the 'fiery tears' of St Lawrence, whose festival is on the 10th of that month. There are other periodic appearances; and Humboldt gives the following epochs as especially worthy of remark: 22d to 25th of April; 17th of July; 10th of August; 12th to 14th of November; 27th to 29th of November; 6th to 12th of December.

It remains to notice briefly the various opinions that have been advanced as to the origin of aerolites, and the theory of meteors in general. The hypotheses that have been formed in answer to the question-Whence come those solid masses that fall upon the earth?-are of two kinds; some ascribing to them a telluric origin, and others making them alien to the earth. Of the first kind, is the conjecture that they may be stones ejected from terrestrial volcanoes, revolving for a time along with the earth, and at last returning to it. Another theory, which at one time found considerable favour, supposed that the matter of which aerolites are composed existed in the atmosphere in the form of vapour, and was by some unknown cause suddenly aggregated and precipitated to the earth. These conjectures are untenable in the face of the facts of the phenomena stated above, and are now completely given up.

suppose the asteroids composing it to be irregularly
grouped, we see a reason why the same stream
should not be always of equal intensity. There may
even be periodicity in this respect too. Between
1799 and 1833-two of the most brilliant manifesta-
tions of the November stream on record-there
elapsed 34 years; and the next brilliant appearances
were in 1866 and 1867, as Olbers had predicted.

We have not space to enter upon such questions
as: What causes the luminous and ignited condition
of aërolites? The height at which many meteors
are seen, puts the action of the atmosphere in causing
ignition out of the question, and the terrestrial
magnetism has been suggested as the exciting cause.
As to those meteors that are unattended by aerolites,
we may suppose that they are merely deflected from
their path by the proximity of the earth, are rendered
luminous through a short arc, and continue their
course with altered orbit. But we are not to assume,
that where no precipitation of matter is visible,
none takes place; it may escape observation, or be
dissipated in powder. See METEORS in SUPP.

AERONAUTICS, the art of navigating the air.
See BALLOON.

AEROSTATICS. This branch of science treats of the equilibrium and pressure of air and other gases, and of the methods of measuring it by the barometer and other instruments. The expansive force or pressure of atmospheric air varies with time and place. In a medium condition of the atmosphere, and the pressure or weight equal to that of a column of near the sea-level, barometrical observations give about 34 feet high. This makes the mean pressure mercury, 30 inches high, or of a column of water of the atmosphere nearly 15 lbs. on every square In seeking a source beyond the earth, the moon inch. This mean pressure of the atmosphere is readily presented itself. Olbers was the first to investigate, 1795, the initial velocity necessary to generally taken as the unit or measure of expansive or elastic forces generally; any particular pressure bring to the earth masses projected from the moon. is said to be equal to so many atmospheres. AeroThis ballistic problem,' as Humboldt calls it, occu- statics also investigates the phenomena of the pied during ten or twelve years the geometricians Laplace, Biot, Brandes, and Poisson. It was calcu- compression of gases; in other words, the relation between the elasticity and the density or volume lated that, setting aside the resistance of air, an of a gas. According to the law of Mariotte, the initial velocity of about 8000 feet in a second, which is about five or six times that of a cannon-ball, would expansive force of one and the same body of gas is suffice to bring the stones to the earth with a velo-Proportional to its density; or, which is the same city of 35,000 feet. But Olbers has shewn, that to different degrees of compression, varies inversely as thing, the expansive force of a body of gas under account for the actual measured velocity of meteoric the space which it occupies. If its elastic force, at stones, the original velocity of projection must be fourteen times greater than the above. It is against into half the space, that force will be 100 lbs. Conone stage, be measured by 50 lbs., when compressed this lunar theory, that we have no proof of active nected with this is the investigation of the variation volcanoes now existing in the moon; and with the of density and pressure in the several vertical strata improvement of the telescope, the probability of the of the atmosphere. It is obvious that the weight of contrary is increasing. It is, accordingly, giving the atmosphere must diminish as we ascend, as part place to the planetary theory, which we noticed at of it is left below; and it results from Mariotte's the outset a theory which harmonises better with the tendency of physical research and of speculation law, that, at different distances from the earth's surface, increasing in arithmetical progression, the generally. atmospheric pressure diminishes in geometrical measuring heights by the Barometer (q. v.). progression. This principle furnishes the means of

The discussion of hypotheses as to the genesis of the recognised planets out of portions of the gradually contracting vaporous mass of the sun; the continued discovery of hitherto unobserved planets between the orbits of Mars and Jupiter; the countless multitudes of comets that are observed traversing our system in all directions, and undergoing appreciable alteration both of consistency and orbit; -all prepare us for the idea, that matter may exist in the inter-planetary spaces, in every variety of form and condition. To account for the phenomena of meteors as above described, we must suppose that there are both detached masses, each revolving in an independent orbit, and giving rise to sporadic meteors; and also connected systems, forming rings or zones round the sun. The intersection of the earth's orbit by such zones or streams, would account for the periodic swarms of meteors; and if we

The elastic force of air and other gases is very
much increased by heat; and consequently, when
allowed, they expand. It is found that a rise of
temperature of 1° of Fahrenheit, causes any gas to
expand of its own bulk; and this expansion is
uniform. If adding 10° to the temperature of a
body of gas increases its bulk 3 cubic inches, an
addition of 20° will give an increase of 6 inches; of
50°, 15 inches, and so on.
by Gay-Lussac, and has been verified by subse-
quent investigators. Both it, however, and that of
Mariotte, can be looked upon as only nearly true,
and that within certain limits.

This law was discovered

AEROSTATIC PRESS. This is a machine used for extracting the colouring-matter from dye-woods

ASCHINESESOP.

ÆSCHYLUS, the father of Greek tragedy, was born at Eleusis, in Attica, 525 B. C. We have but scanty notices of his life. He fought in the battles of Marathon, Salamis, and Platea, witnessed the fall of Darius and Xerxes, and shared in the exulting sentiments which afterwards pervaded liberated Greece. Of the seventy or ninety tragedies ascribed to E., only seven have been preserved Prometheus Bound, the Seven against Thebes, the Persians, Agamemnon, the Choëphori, Eumenides, and the Suppliants. These are sufficient to prove that was the creator of the Greek drama in its higher form. He introduced action in place of the perpetual chorus, and dramatic dialogue to supersede the long narrations of his predecessors Thespis and Chorilus. Scenic effects, masks, and dresses, were other improvements introduced in the plays of E. The plots of his pieces are very simple, and display no ingenuity of construction or solution. His general tone is elevated and earnest, and shews a preference of strong to gentle emotions. Destiny is represented in its sternest aspect; gigantic heroes, Titans, and gods, rather than men, appear on the scene, and the lofty grandiloquence of the language is in accordance with the characters. In the choruses, the language is often turgid and obscure. For some reason, not well known, E. left his native city, and went to Sicily, where he was honourably received by King Hiero. Here he died at Gela, 456 B. C., and the inhabitants of the city raised a monument to his memory. In the poetical translation by Blackie,