Sir,-More has been written in your valuable journal on the subject of aerostation, within the last few months, than during any equal period of time previous. The construction of Green's new and powerful machine, and the astonishing and unequalled trips which have been made with it, seem to have been the chief means of directing public attention more fully to the subject: and though it must be confessed, that little has yet been done towards improving the art, the time seems now come when the scientific world looks upon the subject with very different emotions from what it was wont to do-to endeavour, if possible, to turn to some useful account, what has till now been almost wholly employed to gratify public curiosity. To this end the papers which have appeared in your magazine have most materially assisted; every new fact or suggestion gives fresh interest to the subject; and therefore, every idea bearing upon the subject must be valuable. The subject may be barren, and the soil unfruitful, but by careful cultivation and management, some good fruit must be produced.

Notwithstanding the startling and sudden announcements of Mr. Baddeley and Signor Andervotti, I am inclined to believe that guiding, or propelling balloons, is neither so easy, nor of that simple accomplishment as one might infer from their statements. Nevertheless, from the general information and good sense, which is generally displayed in Mr. Baddeley's communications, I think may safely look forward to his invention with interest. We may be well assured he has not raised the public expectation for the mere purpose of disappointing it? While here, I cannot help pointing Mr. B. to one valuable circumstance in his invention, which he may have overlooked. That is "the upward or downward motion, which can be given without varying

we

the quantity of gas or ballast." Now the ultimate effect of this must be a diminu tion in the size of the balloon (a consummation greatly to be wished), for we shall only want just sufficient gas to raise us from the ground, and we can then, by new power, elevate ourselves to any height we please; we have only to cease in our exertions and we descend, again apply the power and we rise alternately.

I think it is very generally admitted, that nothing can be done, as long as the present shape of balloon is continued. Whilst that is the case the resistance would increase to such an enormous degree, as to set at defiance the power attainable by manual labour. Mr. Mackintosh in a recent Number, referred your readers generally, to a letter of his in No. 637 of your Magazine, and on that letter I wish to make a few observations.

Taking as correct the result of his calculation, that one cubic foot of hydrogen gas has a buoyant power of half an ounce, I will pass to the conclusion he has there jumped at, relative to the total resistance at 30 ft. per second. A cube, the side being 27ft., would present an area of surface equal to 729 square feet; and consequently, the resistance at two lbs. per foot, would be 1458 lbs. instead of 54 lbs. This difference, I imagine, would put a new feature on the subject. How Mr. M. could make so great a mistake in so simple a calculation, seems difficult to ima gine. This calculation, of itself, is suffi cient to show the difficulty attending any mode of propelling, and we must rest our hopes for improvement on a different construction of balloon. What could wings do against such a force? what oars? or what paddle-wheels? to say nothing of their clumsiness; and we may rest assured, that if ever a mode of steering or propelling is found out, it will be by no such unwieldy means.

We now come to the grand idea of em ploying birds to move balloons, by yolking together whole flights of eagles, and bringing them under control by curb and rein. This must be considered as one of those extravaganzas which are sometimes perpetrated by clever men. The subject, to me, appears at once so absurd, as not to merit one moment's consideration; and the following simple calculation may, perhaps, be the means of making a similar

impression on others of your readers. Taking the total resistance at 1458 lbs. as before stated, and assuming with Mr. M. that one eagle can draw 8 lbs., it ap pears that no less a number than 182 would be required! A trifling number, perhaps, in Mr. M.'s eye. This estimate is founded on the resistance encountered by a balloon in its present shape; but supposing we could reduce that resistance three-fourths, it does not appear to reduce the absurdity of the project in any proportion.

Mr. Mackintosh, by this letter, will see of how much importance it is to be correct in our calculations, when the result of those calculations is made the basis on which our after reasonings are built.

Mr. Ogle's suggestion for employing gas as ballast, could never be adopted till we have some more easy method by which the compression of gasses could be effected, as he ought to be aware that every additional atmosphere would give an increasing pressure of 15 lbs. per square inch; and, consequently, it would require vessels of enormous strength to contain sufficient gas to be of any avail.

Mr. Weekes, in the description of a universal eudiometer invented by him, and described in No. 565 of the Mechanics' Magazine, has some beautiful and striking observations on this subject:

"The condensation of gaseous matter, and its consequent conversion thereby to the liquid, and, in some instances, to the solid state, furnishes materials for the basis on which future genius and experience will erect à superstructure of unprecedented magnificence and importance to chemical science, and the mechanical arts of the world. A thousand projects which would now be ridiculed as the day-dreams of the visionary and enthusiast, will find in the successful production of liquid and solid matter from aeriform bodies, more than the ample means of realisation. What, for example, should we think of the adventurous aeronaut who now requires the production of many thousand feet of hydrogen to render buoyant his etherial car, and waft him to the vast altitudes he is capable of thus attaining in the regions of the atmosphere, when he should propose, instead of resorting to the manufac ture of coal-gas, or the slow decomposition of water, for the agency of his flight, to

avail himself of the simple expedient of ress moving compression from the contents of a strong vessel of some cubic inches capacity, preserved at a low temperature, and in the space of a few minutes dilate his splendid. balloon by the rapid transition of solid matter to the gaseous form, and in the next instant spring majestically to the skies!"

When we look back through a long lapse of years, since the discovery of balloons to the present time, and see the little progresss that has been made, we may almost feel ashamed. Man, spurning the ground on which he treads, has found means by which he can elevate himself to heights, emulating the soaring of the eagle, He can descend at will, and re-ascend as pleasure or convenience dictate. But though possessed with such power, yet he has not found equal means whereby the vast machine can be brought properly under his control; but remains suspended in mid-air, between heaven and earth, wafted hither and thither by the caprice of the gentlest wind, unable to steer his course, and unable to alter his horizontal position. Humiliating thought! We see the eagle possesseed of power, not merely sufficient to raise its ponderous body from the earth, but also to give it a velocity outstripping the wings of the wind. And is not man on an equal footing? If nature has forbid him the use of wings to support his body in the air, that defect is amply remedied by mechanical aid. He can command a power sufficient for his easy support, and thus leave him his whole physical force to direct his course; whereas a bird has not only to direct his course, but to support its whole b dy with its wings.

I will now sugg simple mode of propelling balloons, which appears at once so effective, when compared with previous attempts, so simple, and so unexpensive, as to entitle it to serious consideration; and though its power cannot be sufficient to force a balloon against a wind of thirty feet per second, yet I shall be satisfied if it will produce a lower velocity. At all events, I shall be quite content if I can point out a path, which may, perhaps, be easily and successfully trodden by others.

The following sketch will make the description better understood. It is longitudinal section through the balloon and car.

Suppose a to represent the balloon; b, the car; c, a light but powerful air compressor, as large as a man can conveniently work (perhaps a fan would be preferable); d, a flexible pipe proceeding. from the compressor; e, a small air-cham. ber; f, a flexible pipe, with a metal termination at g; h, a slight rod of wood. The modus operandi will now be easily perceived. Air being powerfully forced into e by the compressor c, will escape by the pipe f, and a motion in the opposite direction must be the immediate consequence, varying in velocity as the force exerted at the pump c.

The

effect would be so certain, and the means of applying it so simple and easy, as to leave comparison with any method already known out of the question. It would want no complication of rudder, as a small lateral pipe would effect a revolv-. ing motion, and thus keep the main jet in the proper direction, and the whole of the apparatus would take up the least possible room; whilst by having the compressor to act during the up-and

down stroke, a continued stream of air would be produced. The truth of this statement may be proved in the most easy manner, by simply mounting a small pasteboard air-chamber, on four small wheels, and blowing into it by a very flexible tube. It will be found that with such imperfect means an astonishing velocity will be obtained.

I must now close this letter, which has extended to an unpardonable length, by, leaving the suggestion in the hands of your intelligent readers. I am sure they must acknowledge its simplicity, its com pactness, its little cost, and its effectiveness, when compared with any of the existing methods, which have uniformly been characterised as clumsy and ineffec tive. I am persuaded that it deserves a trial, and that in calm weather it would do that which no other means! has yet. accomplished.

I am, Sir, truly yours,
JOHN LAKE

Gayton, Jan. 19, 1837,

THE NATIONAL GALLERY.

How well acquainted the officers of Government are with the history of their own proceedings-how carefully the House of Commons consults the documents which it orders to be printed, at the public expense, for its use and benefit-may be estimated from the singular history of the erection of the National Gallery, which manifes's an inattention and ignorance on the part of all connected with it which really border on the incredible.

For some time Mr. Wilkins, the architect of the National Gallery, has been in the habit of claiming the merit of having originally suggested the idea of erecting it on its present site-the northern side of Trafalgar-square. He made a positive statement to that effect before the late Committee of the House of Commons respecting the Arts of Design. “Four plans," he said, were laid before a Committee appointed by the Lords of the Treasury-two by Mr. Nash, one by Mr. Cockerell, and my own." This led to an inquiry from Dr. Bowring (Question 1392). "And the number of architects. who were competitors were (sic) confined to those three ?"-"Yes," is the reply;

they were hardly competitors, I do not know whether I ought to call them competitors; plans had been presented by Mr. Nash and Mr. Cockerell, but the fact is, that the suggestion of erecting a building for this purpose originated with me; whether that was a ground of preference or not, I do not know, but I wish to state that. The site was about to be converted into shops, and seeing a very magnificent site, I took the liberty of calling at Lord Dover's and Lord Aberdeen's, and suggesting there would be the site for a National Gallery if one was to be erected."

"Did you make a written representation on the subject?" continues the questioner. "Yes," replies Mr. Wilkins, "and Lord Dover communicated with Lord Grey, in consequence of which I had to wait on Lord Grey." From this statement we observe, that the suggestion was made when Lord Grey was in power-therefore not before 1830and at a time when the site appeared magnificent-therefore after the clearance had been made for Trafalgar-square. As it happens, however, that clearance was made, and Trafalgar-square was formed,

for the express purpose of building the National Gallery where the National Gallery now stands, the originator of the plan was Mr. Nash-it met with the patronage of George IV.-it was proposed by the Commissioners of Woods and Forests-it was sanctioned by the House of Commons-and (it might be added, were it not for the Cimmerian darkness in which parties subsequently appear to have become involved) it became matter of public notoriety in the year 1826, or four years at least before Mr. Wilkins started the bran-new idea, as he imagined, to that trio of very well-informed individuals, Lord Dover, Lord Aberdeen, and Lord Grey. The reader, perhaps, may be disposed to be incredulous about this, if he do not happen to have paid attention to the subject himself, especially as when Mr. Wilkins made his statement there was no one found among the Committee to hint a suspicion of his perfect right to the honour he laid claim to. But by referring to the 14th volume of the House of Commons' Reports for 1826, which contains the Fifth Triennial Report of the Commissioners of Woods, Forests, and Land Revenues, he will find in Appendix, No. 23, plate 3, a "Plan of the Proposed Improvements at Charing-cross, St. Martin's-lane, and Entrance to the Strand," in which an edifice standing on the north side of the then projected square, since made and named Trafalgar, is very legibly labelled, "NATIONAL GALLERY OF PAINTING AND SCULPTURE." In front of it facing towards Whitehall appears another building, intended to be an exact copy of the Parthenon at Athens, and appropriated to the Royal Academy, who have since, to the dissatisfaction of the Committee before which Mr. Wilkins gave evidence, been billeted in the National Gallery itself.

The claim of Mr. Wilkins is, therefore, "baseless as a dream," and his story only. adds another to the numerous instances of the singular ignorance of our artists. and amateurs, respecting what is going on around them in the very sphere with which they ought to be best acquainted. For instance, from the evidence of Sir Francis Chantrey, of Mr. Hawkins, and others, respecting the mode of engraving medals by machinery, this, at least, appears evident, that till a Frenchman came from Paris to solicit support for the im

REMARKS ON MR. SIEVIER'S PATENTS FOR

INDIA-RUBBER MANUFACTURE.

Sir,-Your readers and the public are greatly indebted to you, for laying before them the patented inventions which are to form the basis of the London Caoutchouc Company. On glancing over the objects to which Mr. Sievier has directed his attention, I observe, that, in the first of his patents, cordage is by far the most prominent, as an article of extensive consumption. It does not appear that the presumed improvement, arising from the introduction of caoutchouc, extends beyond the mere giving to cables, ropes, and lines, the property of extending and contracting; which property, it seems, would for some purposes be desirable. Is Mr. Sievier aware that a patent was long since taken out for introducing caoutchouc into these very articles, and that they were not brought into use, and, in fact, could not be used, on account of the rigidity contracted by caoutchouc when exposed to cold? Every body knows that the most flexible piece of caoutchouc that can be produced will become as hard, and as unpliant, as a piece of ash timber of the same dimen. sions, in one cold night. If Mr. Sievier has a remedy against this decisive objection, he has not stated it in his patent, which he should have done if he knew of any. It is easy to see that a cable, for instance, containing a sufficient quantity of caoutchouc to make it elastic at a medium temperature, would in a single night of frost become so inflexibly stiff, that the united efforts of a whole ship's crew would not be able to uncoil it. Let us hope that Mr. Sievier has some clear and explicit explanation to give the public on this point; doubtless your pages will be open to him. The other part of this patent relative to the making elastic, carpet bags or purses, at the mouth, by the introduction of caoutchouc, is an old patented invention, and of little value.

The second patent is for introducing caoutchouc as an elastic into stockings and other articles of dress. A similar contrivance was patented sixteen or seventeen years ago, but it was found that fre quent washing in warm water and soap, soon impaired the elasticity of the caoutchouc; and the application of it at that time went out of use except for gloves, in which it has been used ever since.

The next object of this patent, is the formation of an elastic cloth, with or without a nap, and elastic in both directions, Where can we purchase this cloth? And to what uses has it been applied?

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The last patent was taken out about a year ago for dissolving caoutchouc in liquor ammonia: of what value it may be, I cannot tell. I put some caoutchouc, cut very thin, into “liquor ammonia some months" ago, and the only observable effect is, that the surfaces of the thin slices are softened, and not at all disposed again to become hard, or dry; but beyond this no perceptible effect has been produced. Perhaps Mr. Sievier will inform us, where this solution of caoutchouc, as well as some of the "solid masses of any form" of which he speaks of, are to be purchased, or seen; as until I see these specimens, I for one shall continue to think, that there is some mistake about this solution in liquor ammonia," and the producing any degree of consistency by increasing or diminishing the quantity of water, &c. Many modes of dissolving caoutchouc have been announced, which, when tried, have proved useless; either on account of its never drying, or returning to its original state by evaporation; or, if it did, soon becoming soft again. What prospects the company may have in relation to their mercantile operations, I leave to the examination of others. I look to the patents which you say "it appears the company are to purchase at a considerable expense," which is, I think, in the first instance, the most important part of the business.

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I am, Sir, Your obedient servant, MAINPOINTS.

VENTILATION OF ROOMS.

Sir, I resume my observations on the subject of ventilating rooms. It is a matter of so much interest to people in general, that I think it will induce you