every moment ready to burst. To prevent this, they
introduced a stick through the tube, in order to push
away the inner balloon from its aperture; but the ex-
pansion of the inflammable air pushed it so close, that
all attempts of this kind proved ineffectual.
It was
now, however, become absolutely necessary to give vent
to a very considerable quantity of the inflammable air;
for which purpose the duke de Chartres himself bored
two holes in the balloon, which tore open for the length
of seven or eight feet. On this they descended with
great rapidity; and would have fallen into a lake, had
they not hastily thrown out 60 pounds of ballast, which
enabled them just to reach the water's edge.

The success of the scheme for raising or lowering aerostatic machines by means of bags filled with common air being thus rendered dubious, another method was thought of. This was to put a small aerostatic machine with rarefied air under an inflammable air balloon, but at such a distance that the inflammable air of the latter might be perfectly out of the reach of the fire used for inflating the former; and thus, by increasing or diminishing the fire in the small machine, the absolute weight of the whole would be considerably diUnfortu- minished or augmented. The scheme was unhappily nate voy put in execution by the celebrated M. Pilatre de Rozier, and another gentleman named M. Romaine. Their Messrs Ro-inflammable air balloon was about 37 feet in diameter, zier and and the power of the rarefied air one was equivalent to Romaine. about 60 pounds. They ascended without any appear

age and death of

ance of danger or sinister accident: but had not been long in the atmosphere when the inflammable air balloon was seen to swell very considerably, at the same time that the aeronauts were observed, by means of telescopes, very anxious to get down, and busied in pulling the valve and opening the appendages to the balloon, in order to facilitate the escape of as much inflammable air as possible. A short time after this the whole machine was on fire, when they had then attained the height of about three quarters of a mile from the ground. No explosion was heard; and the silk which composed the air balloon continued expanded, and seemed to resist the atmosphere for about a minute; after which it collapsed, and the remains of the appa-: ratus descended along with the two unfortunate travellers so rapidly, that both of them were killed. M. Pilatre seemed to have been dead before he came to the ground; but M. Romaine was alive when some persons came up to the place where he lay, though he expiredimmediately after.

These are the most remarkable attempts that have been made to improve the science of aerostation; though a great number of other expeditions through the atVoyage of mosphere have taken place. But of all the voyages Messrs Blanchard which had been hitherto projected or put in execution, and Jeffries the most daring was that of M. Blanchard and Dr across the Jeffries across the straits of Dover, which separate straits of Britain from France. This took place on the 7th of January 1785, being a clear frosty morning with a wind, barely perceptible, at N. N. W. The operation of filling the balloon began at 10 o'clock, and, at three quarters after 12, every thing was ready for their departure. At one o'clock M. Blanchard desired the boat to be pushed off, which now stood only two feet distant from that precipice so finely described by Shakespeare in his tragedy of King Lear, As the balloon

Dover.

was scarcely sufficient to carry two, they were obliged to throw out all their ballast except three bags of 10 pounds each; when they at last rose gently; though making very little way on account of there being so little wind. At a quarter after one o'clock, the barometer, which on the cliff stood at 29.7 inches, was now fallen. to 27.3, and the weather proved fine and warm. They had now a most beautiful prospect of the south coast of England, and were able to count 37 villages upon it. After passing over several vessels, they found that the balloon, at 50 minutes after one, was descending, on which they threw out a sack and a half of ballast; but as they saw that it still descended, and with much greater velocity than before, they now threw out all the ballast. This still. proving ineffectual, they next threw out a parcel of books they carried along with them, which made the balloon ascend, when they were about midway between France and England. At a quarter past two, finding themselves again descending, they threw away the remainder of their books, and, ten minutes after, they had a most enchanting view of the French coast. Still, however, the machine descended; and as they had now no more ballast, they were obliged to throw away their provisions, the wings of their boat, and e-. very thing they could possibly spare. "We threw away (says Dr Jeffries) our only bottle, which, in its descent cast out a steam like smoke, with a rushing noise; and when it struck the water, we heard and felt the shock very perceptibly on our car and balloon." All this proving insufficient to stop the descent of the balloon, they next threw out their anchors and cords, and at last stripped off their clothes, fastening themselves to certain slings, and intending to cut away the boat as their last resource. They had now the satisfaction, however, to find that they were rising; and as they passed over the high lands between Cape Blanc and Calais the machine rose very fast, and carried them to a greater height than they had been at any former part of their voyage. They descended safely among some trees in the forest of Guiennes, where there was just opening enough to admit them.

It would be tedious as well as unnecessary to recount all the other aerial voyages that have been performed in our own or other countries: It appeared sufficient for the purpose of this article to notice those which were most remarkable and interesting; and therefore an account of the ingenious Mr Baldwin's excursion from Chester, alluded to above, must not be omitted in our enumeration.

On the 8th of September 1785, at forty minutes past Baldwin's one P. M. Mr Baldwin ascended from Chester in Mr voyage. Lunardi's balloon. After traversing in a variety of different directions, he first alighted, at 28 minutes after three, about twelve miles from Chester, in the neighbourhood of Frodsham, then reascending and pursuing his excursion, he finally landed at Rixton moss, five miles N. N. E. of Wavington, and 25 miles from Chester. Mr Baldwin has published his Observations and remarks made during his voyage, and taken from minutes. Our limits will not admit of relating many of his observations; but the few following are some of the most important and curious. "The sensasation of ascending is compared to that of a strong pressure from the bottom of the car upwards against

E e 2

the

clouds,

the soles of his feet. At the distance of what appeared to him seven miles from the earth, though by the barometer scarcely a mile and a half, he had a grand and most enchanting view of the city of Chester and its View from adjacent places below. The river Dee appeared of a the balloon. red colour; the city very diminutive; and the town entirely blue. The whole appeared a perfect plain, the highest building having no apparent height, but reduced all to the same level; and the whole terrestrial prospect appeared like a coloured map. Just after his first ascent, being in a well watered and maritime part of the country, he observed a remarkable and regular tendency of the balloon towards the sea; but shortly after rising into another current of air, he escaped the danger this upper current, he says, was visible to him at the time of his ascent, by a lofty sound stratum of clouds flying in a safe direction. The perspective appearance of things to him was very remarkable. The Appear- lowest bed of vapour that first appeared as cloud was ance of the pure white, in detached fleeces, increasing as they rose they presently coalesced, and formed, as he expresses it, a sea of cotton, tufting here and there by the action of the air. In the undisturbed part of the clouds, the whole became an extended white floor of cloud, the upper surface being smooth and even.. Above this white floor he observed, at great and unequal distances, a vast assemblage of thunder clouds, each parcel consisting of whole acres in the densest form he compares their form and appearance to the smoke of pieces of ordnance, which had consolidated as it were into masses of snow, and penetrated through the upper surface or white floor of common clouds, there remaining visible and at rest. Some clouds had motions in slow and various directions, forming an appearance truly stupendous and majestic." He endeavours to convey some idea of the scene by a figure; (and from this fig. 1. Plate II. is copied). A represents a circular view he had from the car of the balloon, himself being over the centre of the view, looking down on the white floor of clouds, and seeing the city of Chester through an opening, which discovered the landscape below, limited by surrounding vapour to less than two miles in diameter. The breadth of the outer margin defines his apparent height in the balloon (viz. 4 miles) above the white floor of clouds. Mr Baldwin also gives a curious description of his tracing the shadow of the balloon over tops of volumes of clouds. At first it was small, in size and shape like an egg; but soon inereased to the magnitude of the sun's disc, still grow ing larger, and attended with a most captivating appearance of an iris encircling the whole shadow at some distance round it, the colours of which were remarkably brilliant. The regions did not feel colder, but rather warmer than below. The sun was hottest to him when the balloon was stationary. The discharge of a cannon, when the balloon was at a considerable height, was distinctly heard by the aeronaut; and a discharge from the same piece, when at the height of thirty yards, so disturbed him as to oblige him for safety to lay hold firmly of the cords of the balloon. At a considerable height he poured down a pint bottle full of water; and as the air did not oppose a resistance sufficient to break the steam into small particles, it mostly fell down in large drops. In the course of the balloon's track it was found much affected by the water (a circumstance ob

served in former aerial voyages). At one time the direction of the balloon kept continually over the wa ter, going directly towards the sea, so much as to endanger the aeronaut; the mouth of the balloon was opened, and in two minutes he descended into an under current blowing from the sea: he kept descending, and landed at Bellair farm in Rinsley, 12 miles from Chester.. Here he lightened his car by 31 pounds, and instantly reascending, was carried into the interior part of the country, performing a number of different manoeuvres. At his greatest altitude he found his respiration free and easy. Several bladders which he had along with him crackled and expanded very considerably. Clouds and land, as before, appeared on the same level. By way of experiment, he tried the upper valve two or three times, the neck of the balloon being close: and remarked, that the escape of the gas was attended with a growling noise like millstones, but not near so loud. Again, round the shadow of the balloon, on the clouds be observed the iris. A variety of other circumstances. and appearances he met with, is fancifully described; and at 53 minutes past three he finally landed.

The following is an account of an establishment formed in France during the late war for the improvement of aerial navigation:

France.

"The aerostatic institute, founded by the commit- Aerostatic tee of public safety, and enveloped in the most pro-institute in found secrecy at Meudon, to which also was added a camp for the exercise of the artillery, is even yet looked upon as a secret arrangement of the republic, respecting which the greatest precautions are taken; the doors being shut against the public and all foreigners.

It was impossible to have selected a more convenient spot for the establishment of the aeronautic institute than the royal lodge of Meudon. From its elevated site on a mountain, it commands a beautiful and extensive prospect over a plain covered with villages and cultivated fields, intersected by the Seine, and terminated. by the city of Paris.

The perfection and the rational application of aero- Objects of nautics are the objects of the labours of this establish-it. ment, to which the celebrated natural philosopher Guy-. ton Morveau has in particular rendered the most important services. But the institution stood in need of such a director as Conté, for whom Guyton Morveau has procured the appointment. With a love of the science Conté unites a penetrating genius for research and invention, accompanied by indefatigable assiduity.

The corps of aeronauts, intended to serve in the ar-Employmies of the republic, and consisting of fifty courageous ment of the youths, is trained at the school of Meudon: it is there pupils. the balloons are prepared which are sent off to the armies; and every day in summer the pupils are employed, at one time in performing their exercises, at another in making researches, in natural philosophy, with a balloon which is kept constantly filled for the purpose.

The improvement in the preparation of the balloon, the discovery of a new mode of filling it with inflammable air from the substance of water (hydrogen gas), discovered by Lavoisier, the invention of a new telegraph, connected with the balloon, are the principal advances which have been made in aerostatics at Meudon under the direction of Conté.

The

The old lodge of Meudon serves as a manufactory for the preparation of the balloons, and of all the apparatus necessary to accompany them to the armies. The new lodge is appropriated to the institute, and to the accommodation of the pupils, and of the director and his family. There were prepared the Entreprenant for the army of the north, by means of which the hostile' army was reconnoitered at the battle of Fleurus ; the Céleste for the army of the Sambre and Maese; the Hercule and the Intrepide for the army of the Rhine and Moselle.

very

:

The silk for the balloons is manufactured at Lyons. and is thick and strong and Conté has rendered them much more durable by the precaution of only var nishing the outer surface. The varnish is of an excellent quality; it sufficiently hardens the outside, and does not make the silk stick together when the balloon is folded. Moreover, experience has proved that the inner coat of varnish cannot resist the operation of filling the balloon, that it is corroded by the gas, and that this friction renders the silk flabby.

cylinder is furnished with a pyrometer, and a scale, which, by means of an iron rod, indicates the degrees of rarefaction of the air. A particular point on the scale announces the moment when the cylinders are heated in the degree nearest to fusion: when such is the case, the fire is immediately diminished. The operation of filling a balloon of thirty feet diameter employs one-third of a day.

result of the discoveries made by the great Lavoisier, and has for its basis his important experiment of the decomposition of water. The gas is prepared by the following simple and unexpensive process.

Six or more hollow iron cylinders are set in brick work, beside and over each other, in a furnace which may be constructed in twelve hours; and both ends of each cylinder are made to project from the furnace. The openings of these cylinders are stopped with strong iron covers, through which metal tubes are let in. The tube at one end serves for pouring water, previously heated, into the cylinders when red hot; that on the opposite side is destined to conduct the air which first presents itself, through a reservoir filled with a caustic lixivium, and to convey it into the balloon. The cylinders are partly filled with coarse iron filings, which the excessive heat of the furnace, kept up with pit coal during the whole time of the operation, reduces to a state of excandescence. At this stage of the process, the valve of one of the tubes of each cylinder is opened, and a small quantity of boiling water is gently poured into the heated cylinder. As soon as the vapour of the water touches the heated iron, the two substances which compose the water are separated: the one (the oxygen) attaches itself to the iron, which it calcines, and which after the operation, is found partly crystallized, after the manner of volcanic productions: the other of the component substances of the water (the hydrogen) combines with a quantity of the igneous substance termed calorique, and becomes inflammable air (hydrogen gas), which continues in a permanent state of elastic fluidity, and weighs seven or eight times less than the atmospheric air.

As the water contains a small portion of the substance of carbone (carbonique) which would render the air in the balloon heavy, the air, as it first rushes out of the cylinders, is made to pass through a reservoir of water impregnated with a caustic alkali. This fluid attracts to itself all the carbonique, and nothing rises into the balloon but very pure and inflammable air.

During the operation, it has sometimes happened that the cylinders, heated to excandesence, melted. To guard against this accident, the projecting end of the

car is made fast to the cords which hang down from pupils.
the net the whole of this is done in five minutes. A
colonel then mounts the car with one of the pupils,
and the balloon rises to the height, generally, of from
a hundred and sixty to two hundred and forty yards.
The pupils separate into divisions, for the purpose of
holding the balloon in the air, suffering it to mount,
and drawing it down, by means of three principal
ropes fastened to the net, and ramified with several
others in these manoeuvres they employ the aid of a
capstern. When the balloon has been newly filled,
has yet suffered no evaporation, and still retains all its
force, it requires the strength of twenty persons to
hold it; and in that state it will bear eight hundred
weight. After a space of two months, though much
evaporated, it is still capable of bearing two persons
with their instruments, and even a considerable ballast,
at the same height in the air: but then ten persons are
sufficient to hold it.

The car is constructed of a light lattice work of Form of the wood, lined with prepared leather, and hangs about car. sixteen feet beneath the balloon: it affords convenient room for two persons seated opposite each other, with the necessary instruments for making observations.

The balloon ascends as often in the day as is requi site for the succession of observations which are to be made; but these ascents take place only in calm and serene weather. Whenever any unforeseen accident occurs, the aerial machine is hauled down in five minutes. In strong gusts of wind which suddenly arise, the aeronauts are always exposed to some danger: the balloon, held by the ropes, cannot rise freely; and its vibrations and fluctuations resemble those of a paper kite which has not yet reached a certain degree of altitude. This spectacle, nevertheless, is more terrific to the spectator than to the aeronaut, who, seated in his car, which its own weight preserves in a perpendi cular position under the balloon, is but slightly affected by its desultory motion. No instance of any unfortunate accident has yet occurred at Meudon.

All fear, all idea of danger, vanishes on examining the solidity of the whole apparatus, the precautionary measures adopted with the most prudent foresight and the utmost security, and especially when we are more

particularly

ments.

particularly acquainted with the cool unassuming steadiness of Conté, the director of the whole.

When the return of peace shall allow more leisure, and shall favour the employment of this apparatus in other experiments than those immediately connected with the military service, we may expect to derive from it the most important and diversified advantages to natural science. The experiments will then be conducted under the direction of a committee of naturalists from the national institute, with a view of making discoveries in natural philosophy, meteorology, and Utility of other branches. When the labours of the aerostatic aerostatic institute shall have accomplished ends so important to experithe arts, and of so great general utility, there will be printed a particular account of the establishment, and of the course of experiments pursued: at present, these present, these matters are kept from the knowledge of the public. The most recent invention of Conté, admirable for telegraph. its simplicity and precision, is the aerostatic telegraph. It consists of eight cylinders of varnished black silk, stretched on hoops, and resembling those little pocket lanterns of crimped paper, which draw out and fold down again on themselves. These eight moveable cylinders, each three feet in diameter, and of a proportionate length, are suspended from the bottom of the car, connected together with cords, and hanging one above another, at the distance of four feet. By means of cords passing through the bottom of the car, the aeronautic observers direct those cylinders, give them different positions at will, and thus carry on their telegraphic correspondence from the regions of the air.

Aerostatic

Ascent of a

Fleurus.

Conté has further applied his thoughts to the invention of a similar aerostatic telegraph, which, without the assistance of a great balloon, or an aërial correspondent, should be managed by a person standing on the ground, by means of cords; the apparatus being suspended to a small balloon, of only twelve feet di

ameter.

Coutel, captain of the aeronautic corps, was the man balloon at who ascended with the Entreprenant balloon on the the battle of 26th of June, 1794, and who conducted the wonderful and important service of reconnoitring the hostile armies at the battle of Fleurus, accompanied by an adjutant and a general. He ascended twice on that day, to observe, from an elevation of four hundred and forty yards, the position and manoeuvres of the enemy. On each occasion he remained four hours in the air, and, by means of preconcerted signals with flags, carried on a correspondence with General Jourdan, the commander of the French army.

His intended ascent had been made known to the enemy, who, at the moment when the balloon began to take its flight, opened the fire of a battery against the aeronauts. The first volley was directed too low : one ball, nevertheless, passed between the balloon and the car, and so near to the former, that Coutel imagined it had struck it. When the subsequent discharges were made, the balloon had already reached such a degree of altitude, as to be beyond the reach of cannon shot, and the aeronauts saw the balls flying beneath the car. Arrived at their intended height, the observers, remote from danger, and undisturbed, viewed all the evolutions of their enemies, and, from the peaceful regions of the air, commanded a distinct and com

prehensive prospect of two formidable armies engaged in the work of death." (Month. Mag. vol. vi. p. 337-).

remarkable

On the 28th of June 1802, M. Garnerin, a French Garnerin's aeronaut, in company with an English gentleman, as- voyage in cended in a balloon of 20 feet diameter from Ranelagh England gardens. They passed over London, rose to the height for its rapiof 10,000 feet, and landed in three quarters of an hour dity. from the time of their ascent on a common near Colchester, a distance of near 60 miles from London. The temperature of the air when they ascended to the clouds. was 15 degrees lower than on the surface of the earth; but when they rose above the clouds, it became sensibly milder. The rapidity of M. Garnerin's voyage is unequalled in the history of aerostation.

The frequency of aërial voyages, accompanied with Uses of ac particular details of trifling and uninteresting circum-rostation. stances, and apparently made with a view to promote the interests of particular persons, regardless of any advancement in knowledge, had sunk the science of aerostation so low in the opinion of most people, that before we give an account of the most proper methods of constructing these machines, it is necessary to premise something concerning the uses to which they may possibly be applied. These, according to Mr Cavallo, are the following:

"The small balloons, especially those made of paper, and raised by means of spirit of wine, may serve to explore the direction of the winds in the upper regions of the atmosphere, particularly when there is a calm below; they may serve for signals in various circumstances, in which no other means can be used; and letters or other small things may be easily sent by them, as for instance from ships that cannot safely land on account of storms, from besieged places, islands, or the like. The larger aerostatic machines may answer all the above mentioned purposes in a better manner; and they may, besides, be used as a help to a person who wants to ascend a mountain, a precipice, or to cross a river; and perhaps one of these machines tied to a boat by a long rope, may be, in some cases, a better sort of sail than any that is used at present. The largest sort of machines, which can take up one or more men, may evidently be subservient to various economical and philosophical purposes. Their conveying people from place to place with great swiftness, and without trouble, may be of essential use, even if the art of guiding them in a direction different from that of the wind should never be discovered. By means of those machines the shape of certain seas and lands may be better ascertained; men may ascend to the tops of mountains they never visited before; they may be carried over marshy and dangerous grounds; they may by that means come out of a besieged place, or an island; and they may, in hot climates, ascend to a cold region of the atmosphere, either to refresh themselves, or to observe the ice, which is never seen below; and, in short, they may thus taken to several places, to which human art hitherto knew of no conveyance.

be

"The philosophical uses, to which these machines may be subservient, are numerous indeed and it may be sufficient to say, that hardly any thing which passes in the atmosphere is known with precision, and that principally for want of a method of ascending into it. The formation of rain, of thunder storms, of vapours;

sion.

Experi

ments

bail, snow, and meteors in general, require to be attentively examined and ascertained. The action of the barometer, the refraction and temperature of the air in various regions, the descent of bodies, the propagation of sound, &c. are subjects which all require a series of observations and experiments, the performance of which could never have been properly expected before the discovery of aerostatic machines."

To these uses we may add the gratification of curiosity and pleasure, as a very strong inducement to the practice of an art, in which, with any tolerable degree of caution, there appears not to be the smallest danger. Every one who has tried the experiment testifies, that the beauty of the prospect afforded by an ascent, or the pleasure of being conveyed through the atmosphere, cannot be exceeded. No one has felt the least of that giddiness consequent upon looking from the top of a very high building or of a precipice, nor have they any of the sickness arising from the motion of a vessel at sea. Many have been carried by balloons at the rate of 30, 40, or even 50 miles an hour, without feeling the least inconvenience, or even agitation of the wind; the reason of which is, that as the machine moves with nearly the velocity of the wind itself, they are always in a calm, and without uneasiness. Some have apprehended danger from the electricity of the atmosphere; and have thought, that a stroke of lightning, or the smallest electric spark, happening near a balloon, might set fire to the inflammable air, and destroy both the machine and the adventurers. Mr Cavallo has suggested several considerations for diminishing apprehensions of this kind. Balloons have been already raised in every season of the year, and even when thunder has been heard, without injury. In case of danger, the aeronauts may either descend to the earth, or ascend above the region of the clouds and thunder storms. Besides, as balloons are formed of materials that are not conductors of electricity, they are not like to receive strokes, especially as by being encompassed with air, they stand insulated. Moreover, inflammable air by itself, or unmixed with a certain quantity of common air, will not burn; so that if an electric spark should happen to pass through the balloon, it would not set fire to the inflammable air, unless a hole was made in the covering.

Principles The general principles of aerostation are so little of acrosta different from those of hydrostatics, that it may seem superfluous to insist much upon them. It is a fact universally known, that when a body is immersed in any fluid, if its weight be less than an equal bulk of that fluid, it will rise to the surface; but if heavier, it will sink; and if equal, it will remain in the place where it is left. For this reason smoke ascends into the atmosphere, and heated air in that which is colder. The ascent of the latter is shown in a very easy and satisfactory manner by bringing a red-hot iron under one of heated air. the scales of a balance, by which the latter is instantly made to ascend; for as soon as the red-hot iron is brought under the scale, the hot air being lighter than that which is colder, ascends, and strikes the bottom, which is thus impelled upwards, and the opposite scale descends, as if a weight had been put into it.

showing the impulse of

Upon this simple principle depends the whole theory of aerostation; for it is the same thing whether we render the air lighter by introducing a quantity of

By

heat into it, or enclosing a quantity of gas specifically lighter than the common atmosphere in a certain space; both will ascend, and for the same reason. A cubic foot of air, by the most accurate experiments, has been found to weigh about 554 grains, and to be expanded by every degree of heat, marked on Fahrenheit's thermometer, about 3th part of the whole. heating a quantity of air, therefore, to 500 degrees of Fahrenheit, we shall just double its bulk when the thermometer stands at 54 in the open air, and in the same proportion we shall diminish its weight; and if such a quantity of this hot air be enclosed in a bag, that the excess of the weight of an equal bulk of common air weighs more than the bag with the air contained in it, both the bag and air will rise into the atmosphere, and continue to do so until they arrive at a place where the external air is naturally so much rarefied that the weight becomes equal: and here the whole will float.

The power of hot air in raising weights, or rather that by which it is itself impelled upwards, may be shown in the following manner: Roll up a sheet of paper into a conical form, and, by thrusting a pin into it near the apex, prevent it from unrolling. Fasten it then, by its apex, under one of the scales of a balance by means of a thread, and, having properly counterpoised it by weights, put it into the opposite scale; apply the flame of a candle underneath, you will instantly perceive the cone to arise, and it will not be brought into equilibrium with the other but by a much greater weight than those who have never seen the experiment would believe. If we try this experiment with more accuracy, by getting proper receptacles made which contain determinate quantities of air, we shall find that the power of the heat depends much more on the capacity of the bag which contains it than could well be supposed. Thus, let a cubical receptacle be made of a small wooden frame covered with paper, capable of containing one foot of air, and let the power of a candle be tried with this as above directed for the paper cone. It will then be found that a certain weight may be raised; but a much greater one will be raised by having a receptacle of the same kind which contains two cubic feet; a still greater by one of three feet; a yet greater by one of four feet, &c. and this even though the very same candle be made use of; nor is it known to what extent even the power of this small flame might be carried.

to be made

From these experiments it appears, that in the aero- Rarefied static machines constructed on Montgolfier's plan, it air balmust be an advantage to have them as large as possible; loons ought because a smaller quantity of fire will then have a great- as large as er effect in raising them, and the danger from that ele- possible. ment, which in this kind of machine is chiefly to be dreaded, will be in a great measure avoided. On this How balsubject it may be remarked, that as the cubical conloons might tents of a globe, or any other figure of which balloons rise by the are made, increase much more rapidly than their sur-heat of faces, there must ultimately be a degree of magnitude the atmos at which the smallest imaginable heat would raise any phere. weight whatever. Thus, supposing any aerostatic machine capable of containing 500 cubic feet, and the air within it to be only one degree hotter than the external atmosphere; the tendency of this machine to rise, even without the application of artificial heat, would

ba

common