a

Fig. 10.

screw.

directs the adze through the space between his two | used to illustrate the cause and generation of the feet; he thus surprises us by the quantity of wood wind, although it is simply an instrument for converting water into steam. It consists of a hollow ball of metal sometimes made in the form of a human face in the act of blowing, with a slender pipe with a narrow orifice issuing from the mouth of the figure, or inserted into the ball by means of a shouldered The ball being filled with water and the pipe screwed in, the flame of a spirit lamp or the heat of burning charcoal is applied to it, and the water being heated, high pressure steam is formed, which escapes with a great noise from the jet, and with sufficient force to turn round a small vaned wheel opposed to it. Of course the stronger the heat the more elastic and violent will be the steam. Care must be taken that the jet is not stopped up, or the ball may burst and lead to danger. The æolipile is now regarded as only a scientific toy of no practical use, and of very little use to the scientific lecturer, who has better means at his disposal for illustrating the generation and force of steam.

removed. In fine works he frequently places his toes over the spot to be wrought, and the adze penetrates 2 or 3 inches beneath the sole of the shoe, and he thus surprises us by the apparent danger, yet perfect working of the instrument, which in the hands of the shipwright in particular, almost rivals the joiner's plane. It is with him the nearly universal paring instrument, and is used upon works in all positions." The small Indian adze or Bassoolah d, instead of being circular like the European adze, is formed at a direct angle of 45° or 50°. Its handle is only 12 or 13 inches long, and the tool is used with great precision by the motion of the elbow joint. It is grasped so near the head that the forefinger rests on the metal, the thumb nearly on the back of the handle, the other fingers grasp the front of it, the nails approaching e ball of the thumb. The wrist is held firmly, the stroke being made principally from the elbow, the inclination of the cutting face being nearly a tangent to the circle described by the instrument round the elbow joint as a centre, the exact adjustment being made by the grasp and the inclination of the wrist, which is soon acquired by a little practice. In this way very hard woods may be dressed for the lathe, with a degree of ease and accuracy not attainable with the small axe used in this country.

In order to grind any one of the adzes just noticed the handle must be removed, and this is easily done, as the eye of the tool is larger externally than internally, as in the common pickaxe, so that the tool cannot fly off when in use, but a blow on the end of the handle easily removes it.

EOLIPILE, (from pila Eoli, the ball of Eolus, or of the god of the winds,) an instrument formerly

(1) Holtzapffel on Turning and Mechanical Manipulation, vol. ii. London, 1847.

AERATED WATERS. [See CARBONIC ACIDSODA WATER.]

AEROSTATION and AEROSTATICS, standing in the air, from anp, the air, and orŋμ, to stand, or Oráois, standing. AERONAUTICS, sailing in the air, from anp, the air, and vaûs, a ship. This subject ought scarcely to find a place in a work devoted to the useful arts, because aërostation has rarely been applied to any useful purpose. The art of flying in the air had been a favourite problem with learned and scientific men from the times of antiquity; but there is no authentic account of the problem having been solved until towards the close of the last century, when the brothers Montgolfier invented a machine which they called a ballon or little ball, from which we derive the word balloon. About the same period Cavendish, in England, discovered hydrogen gas, and proved it to be the lightest of all ponderable substances; it therefore occurred to Dr. Black, in 1767 or 1768, that a light envelope filled with this gas would ascend. The experiment was tried by Cavallo, in 1782, but he did not succeed in causing anything heavier than a soap-bubble to ascend. The first balloon that was actually launched into the air, was constructed by Stephen and Joseph de Montgolfier, paper-makers at Annonay, near Lyons. It occurred to them that a thin paper envelope might be employed to confine hydrogen gas in such a way as to cause it to ascend, but they found that the gas escaped so rapidly through the pores of the paper that it could not be depended on. They then conceived the idea that heat might be employed to rarefy the air enclosed in their balloon. The experiment was tried, and a balloon of coarse linen, lined with paper, of the capacity of 23,000 cubic feet, (French,) was found to have a power of lifting about 500lbs. including its own weight. This trial was so successful that the Montgolfiers thought they had completely. solved the celebrated problem of flying or sailing in the air. They even suggested that "large balloons might be employed for victualling a besieged town,

it

for raising wrecked vessels, perhaps even for making this gentleman, accompanied by the Marquis d'Arlandes "It rose voyages, and certainly in particular cases for observa- ascended in a montgolfière at 1.54, P. M. tions of different kinds, such as reconnoitring the in the most majestic manner, and when it was about position of an army,' or the course of vessels at 25 270 feet high, the intrepid voyagers took off their or even 30 leagues distance, &c." A public exhi-hats and saluted the spectators. No one could help bition was made of a montgolfière, (as this kind of feeling a mingled sentiment of fear and admiration. balloon was called, to distinguish it from the hydrogen- The voyagers were soon undistinguishable, but the gas balloon,) in the market-place of Annonay, on the machine, hovering in the air, and displaying the 5th June, 1783. The montgolfière was constructed of most beautiful figure, rose at least 3,000 feet high, It crossed the immense folds of linen buttoned together, and fixed and remained visible all the time. to a frame 110 feet in circumference, the whole Seine below the barrier of La Conférence; and weighing about 500lbs., and containing 22,000 cubic passing thence between the Ecole Militaire and the feet (French) of air. On applying fire to the Hôtel des Invalides, was in view of all Paris. The opening at the bottom of the balloon, the mass gra- voyagers, satisfied with their experiment, and not dually swelled out into a large globe, and was with wishing to travel further, agreed to descend; but difficulty prevented from rising. At length it was seeing that the wind was carrying them upon the liberated, and rose with great rapidity. In less than houses of the Rue de Sève, Faubourg St. Germain, 10 minutes it gained an elevation of 1,000 toises. It they preserved their presence of mind, increased the then moved in a horizontal line, and gradually de- fire, and continued their course through the air till scended. The success of this experiment excited the they had crossed Paris. They then descended quietly greatest interest all over Europe, especially in Paris, on the plain, beyond the new Boulevard, opposite the where it was immediately resolved to repeat the mill of Croulebarde, without having felt the slightest experiment with hydrogen gas instead of heated air. inconvenience, and having in the car two-thirds of A balloon was formed of lutestring, and varnished their fuel. They could then, if they had wished, have with India rubber, and on the 23d August it was gone three times as far as they did go, which was filled with hydrogen gas, procured by the action of 5,000 toises, done in from 20 to 25 minutes. The dilute sulphuric acid and iron filings. Considerable machine was 70 feet high, 46 feet in diameter; difficulty was experienced in filling it; but the gas contained 60,000 cubic feet, and carried a weight of not having been washed by passing it through cold from 1,600 to 1,700lbs." water, entered the balloon hot, and charged with acid fumes, so that it injured the envelope, and loaded it with moisture. As much as 500lbs. of sulphuric acid, and twice that weight of iron filings were expended before the balloon was completely filled. At length it rose, and was kept suspended at the height of 100 feet above the ground. In this state it was conveyed with acclamations to the Place des Victoires, and about midnight it was transported in silent procession to the Champ de Mars, proceeded by torches, and guarded by horse and foot soldiers; the people were filled with astonishment, and many of them saluted it respectfully as it passed. On the 27th, it was again filled, and allowed to ascend. It remained threequarters of an hour in the air, and fell five leagues from Paris. On the 19th September, one of the Montgolfiers being in Paris, sent up one of his balloons with an attached car containing a sheep, a cock and a duck. These were therefore the first aërial voyagers. M. Pilatre de Rozier was their immediate successor, but he deemed it prudent to have a rope attached to the balloon and held by persons below, so that he might not be entirely launched into the air. At length, on the 21st November, 1783,

(1) This idea was actually practised at the battle of Fleurus in 1794, in which the French, under General Jourdan, gained a decisive victory over the Austrian forces, which has been ascribed principally to the accurate information of the enemy's movements before and during the battle, communicated by telegraphic signals from a balloon sent up to a moderate height. The aeronauts, at the head of whom was the celebrated chemist Guyton-Morveau, mounted twice in the course of the day, and continued about 4 hours each time hovering in the rear of the army. In the second ascent the enemy opened a battery against the balloon, but the aëronauts soon rose to a height above the reach of cannon.

The second ascent was by Messrs. Charles and Robert, on the 1st December, 1783, in a balloon filled with hydrogen.' They ascended from the Tuileries at Paris, and in an hour and three-quarters alighted on the meadow of Nesle, 25 miles from Paris. Finding that the balloon was still buoyant, M. Charles ventured alone upon a second ascent. The sun had set, and it was getting dark, but he ascended with great velocity, and reached a height of 2 miles in about ten minutes. The sun rose again to him in full orb, and as he says, "I was the only illuminated object, all the rest of nature being plunged in shadow." A screen of vapour concealed the earth from view, while the moon scattered gleams of various hues over the fantastic and changing forms of the clouds beneath. The air was very cold; the balloon appeared to be fully distended, and upon opening the valve, the gas rushed out like a misty vapour. He descended slowly, and alighted in safety near the forest of Tour du Lay, having travelled 9 miles in 35 minutes. The barometer at the greatest elevation fell to 20.05 inches, giving an elevation of about 9,700 feet. The thermometer sank to 21° Fahr. A short time before this ascent, a small pilot or messenger fire-balloon was launched by Montgolfier; this was found to have proceeded in an opposite direction, which first gave rise to the suspicion of the existence of different currents of air at different heights. On the 2d March, 1784, M. Blanchard ascended

(1) Some idea may be formed of the expense of ballooning at this early period in the history of the art, from the fact that this apparatus cost 4007. sterling, one half of which was expended in the production of the gas alone.

balloons for the purpose of military reconnaissance. | sophers, in presence of a few friends, embarked In the early part of the French revolution a balloon, in the car at ten o'clock in the morning of the 23d prepared under the direction of the Aërostatic Institute in the Polytechnic School, and entrusted to the command of two or three experienced officers, was distributed to each of the republican armies. These balloons were of a more solid and perfect construction than the toy machines hitherto exhibited. They were filled by a far more economical method than that before adopted, namely, by passing steam of water through six iron cylinders charged with iron turnings, and heated to redness in a simple kind of furnace; the oxygen of the steam uniting with the iron, while the hydrogen gas being disengaged was first passed through a reservoir of caustic lye before it entered the balloon. By this contrivance a balloon 30 feet in diameter could be filled in about 4 hours at a very moderate expense.

As the aeronautic voyages hitherto undertaken had contributed almost no results to science, the French philosophers were anxious to employ one of the balloons of the Aërostatic Institute, for the purpose of making a set of observations in the higher regions of the air. In July, 1803, Messrs. Robertson and Lhoest had ascended from Hamburg to a height of nearly 3 miles, and had given out a statement of results, the accuracy of which had been called in question. To verify these, and also to settle other interesting points, Messrs. Biot and Gay-Lussac proposed to the French government to make an ascent. Their offer was seconded by Berthollet and Laplace, and Chaptal, then minister of the interior, gave it his warm support.' The balloon which had once visited Egypt was delivered to the custody of Biot and GayLussac; and the same artist who constructed it was ordered to refit and prepare it under their direction at the public expense. Besides the usual provision of barometers, thermometers, hygrometers, and electrometers, they had two compasses, and a dipping needle, with another fine needle, carefully magnetized, and suspended by a very delicate silk thread, for ascertaining by its vibrations the force of magnetic attraction. To examine the electricity of the different strata of the atmosphere, they carried several metallic wires, from 60 to 300 feet in length, and a small electrophorus freely charged. For galvanic experiments they had procured a few discs of zinc and copper, with some frogs, to which they added insects and birds. It was also intended to bring down a portion of air from the higher regions, to be subjected to a chemical analysis; and for this purpose a flask, carefully exhausted, and fitted with a stopcock, had been prepared.

The balloon was placed in the garden of the Conservatoire des Arts, and no pains were spared in providing whatever might contribute to the greater safety and convenience of the voyagers. Everything being ready for their ascent, these adventurous philo

(1) Our account of this scientific aërial voyage is condensed from Sir John Leslie's excellent notice contained in the article "Aeronautics" in the Encyclopædia Britannica.

of August, 1804. The barometer was then at 30.13 inches, the thermometer at 61.7° Fahr., and Saussure's hygrometer pointed at 80.8°, or very near the limit of absolute humidity. They rose with a slow and imposing motion. Their feelings were at first absorbed in the novelty and magnificence of the spectacle which opened before them; and their ears were saluted with the buzz of distant gratulations, sent up from the admiring spectators. In a few minutes they entered the region of the clouds, which seemed like a thin fog, and gave them a slight sensation of humidity. The balloon had become quite inflated, and they were obliged to let part of the gas escape, by opening the upper valve; at the same time, they threw out some ballast, to gain a greater elevation. They now shot through the range of clouds, and reached an altitude of about 6,500 English feet. These clouds viewed from above had the ordinary whitish appearance; they all occupied the same height, only their upper surface seemed marked with gentle swells and undulations, exactly resembling the aspect of a wide plain covered with snow.

Our voyagers now began their experimental operations. The magnetic needle was attracted as usual by iron; but they found it impossible at this time to determine with accuracy its rate of oscillation, owing to a slow rotatory motion with which the balloon was affected. In the meanwhile, therefore, they made other observations. A Voltaic pile, consisting of twenty pairs of plates, exhibited all its ordinary effects, gave the pungent taste, excited the nervous commotion, and occasioned the decomposition of water. By rejecting some more ballast, they had attained the altitude of 8,940 feet, but afterwards settled to that of 8,600 feet. At this great elevation, the animals which they carried with them appeared to suffer from the rarity of the air. They let off a violet bee, which flew away very swiftly, making a humming noise. The thermometer had fallen to 56.4° Fahr., yet they felt no cold, and were, on the contrary, scorched by the sun's rays, and obliged to lay aside their gloves. Both of them had their pulses much accelerated. That of Biot, which generally beat 79 times in a minute, was raised to 111; while the pulse of his friend, Gay-Lussac, a man of a less robust frame, was heightened from 60 to 80 beats in the minute. Notwithstanding their quickened pulsation, however, they experienced no sort of uneasiness nor any difficulty in breathing.

What perplexed them the most was the difficulty of observing the oscillations of a delicately suspended magnetic needle. But they soon remarked, on looking attentively down upon the surface of the conglomerated clouds, that the balloon slowly revolved, first in one direction, and then returned the contrary way. Between these opposite motions there intervened short pauses of rest, which it was necessary for them to seize. Watching, therefore, the moments of quiescence, they set the needle to vibrate, but were unable to count more than five, or very rarely ten

The hygrometer, or rather hygroscope, of Saussure, advanced regularly towards dryness in proportion to the altitude which they attained. At the elevation of 13,000 feet it had changed from 80.8° to 30°. But still the conclusion that the air of the higher strata is drier than that of the lower, we are inclined to consider as fallacious. In fact the indications of the hygroscope depend on the relative attraction for humidity possessed by the substance employed, and the medium in which it is immersed. But air has its disposition to retain moisture always augmented by rarefaction, and consequently such alteration alone must materially affect the hygroscope. The only accurate instrument for ascertaining the condition of the air, with respect to dryness, is founded on a property of evaporation.

oscillations. A number of trials made between the | general standard, owing to the copious descent of cold altitudes of 9,500 and 13,000 feet, gave 7" for the portions of air from the highest regions. mean length of an oscillation, while at the surface of the earth it required 7" to perform each oscillation. A difference so very minute as the 140th part could be imputed only to the imperfection of the experiment; and it was hence fairly concluded that the force of magnetic attraction had in no degree diminished at the greatest elevation they could reach. The direction of this force, too, seemed, from concurring circumstances, to have continued the same; though they could not depend on observations made in their vacillating car with so delicate an instrument as the dipping needle. At the altitude of 11,000 feet they liberated a green linnet, which flew away directly; but soon feeling itself abandoned in the midst of an unknown ocean, it returned and settled on the stays of the balloon. Then mustering fresh courage it took a second flight, and dashed downwards to the earth, describing a tortuous, yet almost perpendicular track. A pigeon which they let off under similar circumstances afforded a more curious spectacle. Placed on the edge of the car, it rested a while, measuring as it were the breadth of that unexplored sea which it designed to traverse; now launching into the abyss, it fluttered irregularly, and seemed at first to try its wings in the thin element; till, after a few strokes, it gained more confidence, and, whirling in large circles or spirals, like the birds of prey, it precipitated itself towards the mass of extended clouds, where it was lost from sight.

It was difficult in those lofty and rather humid regions, to make electrical observations; and the attention of the scientific navigators was, besides, occupied chiefly by their magnetical experiments. However, they let down from the car an insulated metallic wire of about 250 feet in length, and ascertained, by means of the electrophorus, that the upper end indicated resinous or negative electricity. This experiment was several times repeated; and it seemed to corroborate fully the previous observations of Saussure and Volta relative to the increase of electricity met with in ascending the atmosphere.

The diminution of temperature in the higher regions was found to be less than what is generally experienced at the same altitude on mountains. Thus, at the elevation of 12,800 feet, the thermometer was at 51° Fahr., while it stood as low as 631° at the Observatory; being only a decrement of one degree for each 1,000 feet of ascent. This fact corresponds with the observations made by former aëronauts, and was probably produced by the operation of two different causes. First, the rays from the sun, not being enfeebled by passing through the denser portion of the atmosphere, would act with greater energy on the balloon and its car, and consequently affect the thermometer placed in their vicinity. Next, the warm current of air, which during the day rises constantly from the heated surface of the ground, must augment the temperature of any body which is exposed to its influence. During the night, on the contrary, the upper strata of the atmosphere would probably be found colder than the

The ballast being now almost quite expended, it was resolved to descend. The aeronauts, therefore, pulled the upper valve and allowed part of the hydrogen to escape. They dropped gradually, and when they came to the height of 4,000 feet they met the stratum of clouds extending horizontally, but with a surface heaved into gentle swells. When they reached the ground, no people were near them to stop the balloon, which dragged the car to some distance along the fields. From this awkward and even dangerous situation they could not extricate themselves without discharging the whole of their gas, and therefore giving up the plan of sending M. Gay-Lussac alone to explore the highest regions. It has been reported that his companion, M. Biot, though a man of activity, and not deficient in personal courage, was so much overpowered by the alarms of their descent, as to lose for the time the entire possession of himself. The place where they alighted, at half-past one o'clock, after three hours and a half spent in the midst of the atmosphere, was near the village of Meriville, in the department of the Loiret, and about fifty miles from Paris.

It was the desire of several philosophers at Paris that M. Gay-Lussac should mount a second time, and repeat the different observations at the greatest elevation he could attain. Experience had instructed him to reduce his apparatus, and to adapt it better to the actual circumstances. As he could only count the vibrations of the magnetic needle during the very short intervals which occurred between the contrary rotations of the balloon, he preferred one of not more than six inches in length, which, therefore, oscillated quicker. The dipping needle had been magnetized and adjusted by M. Coulomb. To protect the thermometer from the direct action of the sun, it was enclosed within two concentric cylinders of pasteboard covered with gilt paper.

The hygrometers, which were made with four hairs, were sheltered nearly in the same way. The two glass flasks, intended to bring down air from the highest regions of the atmosphere, had been exhausted till the mercurial gauge stood at the 25th part of an inch, and their stopcocks were so perfectly fitted that after the lapse of eight days they still preserved their