Lapas attēli
PDF
ePub

had frost when he told us to look for thaw, and vice versa; thus in a slight degree lessening the value of his labours, and pretty well justifying him in considering his first attempt at weather-wisdom any thing but a "lucky hit." But even this miserable shift will not serve his turn with regard to his general prophecy, that the "tendency of the month would be to drought,"-this January, as if on purpose to cut every inch of ground from under him, having been decidedly the wettest known for many years. He has, however, another starting-hole." "Only wait," he cries, till we have news from America, though all my predictions have gone wrong here, I feel confident they have been found quite correct in the Western hemisphere!" (Alas! for the Meteorological Society.)

American Electro-Magnetic Engine. A New York paper states, "We learn that Messrs. Davenport and Cook, of Saratoga, after three years' study and attention, had perfected an electro-magnetic engine, consisting of a stationary-magnetic circle, formed of disconnected segments. These segments are permanently charged magnets, the repelling poles of which are placed contiguous to each other. Within the circle stands the motivewheel, having projecting ga vanic magnets, which revolve as near the circle as they can be broughtwithout actual contact. The galvanic magnets are charged by a battery, and when so charged, mag netic attraction and repulsion are both brought into requisition in giving motion to the wheel-the poles of the galyan e magnets being changed more than 1000 times per minute."

China versus Lyons.-The silk-manufacturers of Lyons have lately begun to complain that they are losing the custom of the United States. For some time, it is said, the Americans have shown a preference for the manufactures of China, and of late they have conveyed thither specimens of the newest patterns from Lyons for the purpose of getting them imitated by the Chinese. The result has been such an abundant supply of Chinese silks in the American market, that the United States now export them to foreign countries. If this be really the case, it supplies or reason to admire the cunning than the fair play of brother Jonathan, and may tend to show that, until some general law of copyright is adopted by the nations of Christendom, a pre-eminence in any branch of art, however it may contribute to national glory, can by no means be reckoned on as a sure source of national wealth.

Alderman Wood's Metropolitan Improvements.The Report of the House of Commons' Committee on Alderman Wood's proposed metropolitan improvements has just appeared. It is by no means of alarming dimensions, as, including the appen dix, it comprises on y fifty-four pages folio. The lithographic plans which accompany it, fifteen in number, convey almost the whole information that is given respecting the proposed improvements. These we shall take an early opportunity of analyzing.

Action of Light on Dyed Colours.-M. Chevreuil, of the French Academy of Sciences, has recently laid before that Society an a count of a series of chemical investigations entered into by him with relation to the art of dyeing. One of the most curious of these relates to the action of light on artificial colours, which has hitherto been supposed to be most deleterious, but is proved by M. Cherreuil's experiments to be almost entirely innocent

unless in conjunction with the air, with hydrogen, &c. He enclosed some specimens of dyed stuffs in bottles, from which the air was exhausted; and at the end of two years, although constantly exposed to the light, the colours had hardly sustained any alteration. Some other specimens of the same kind of stuffs, dyed by the same materials, were carefully kept from the light, but exposed to the

air during the same space of time, and the result was that the colours had entirely disappeared. Might not this experiment supply a useful hint to the curators of the British and other Museums, in which valuab'e but easily destructible objects are kept in glass-cases?

Mr. Crosse's Experiments.-Mr. Von Humboldt recently presented to the French Academy of Sciences, some specimens of semi-transparent gun flint, in which, without any process of dissolving or beating small, a multitude of infusory animalcules might be discovered. Does not this circumstance tend to throw a light on the recent interesting experiments of Mr. Crosse, of Broomfield, described in page 384 of the Mechanics' Magazine? Although, as Mr. Crosse observes, neither acid, nor wood, nor flannel, nor iron ore, was one of the constituent parts of the compound from which in the second case insects were observed to emerge; yet both in that case, and in the preceding one, solution of silieute of potash was a principal ingredient, and gunflint is a species of silex. It would thus appear, that the Voltaic action had properly nothing to do with the production of these insects which may have previously existed in the silex.

"New Manchester."-The Austrians appear determined to throw off their old character of a quiet and prosperous agricultural nation, and enter with all their might into the lists of commerce and manufactures. To the project for rendering na. vigable and navigating the Danube, is now added that for canal, to be called the Lewes-canal, to connect the Danube with the Maine, and thus with the Rhine and German Ocean It is calculated, that when this new road for commerce is opened, the Austrian capital will become the grand centre for the traffic to be carried on between Holland, Asia Minor, and the intervening countries. Not content with this, however, the citizens of Vienna are, it is stated in soure of the foreign papers, about to establish a "new Manchester" all at once in the Brigitten-au (or Bridget's Meadow), near that city, in which, however, the motive force is not, as in its prototype, to be the power of steam, but the power of water. We would advise the projectors of this scheme not to be too sanguine in their anticipations. Neither Rome nor Manchester was built in a day.

The Remarks on the Birmingham Railway Report are unavoidably deferred till our next.

[merged small][ocr errors][merged small][merged small][merged small]

Mechanics' Magazine,

MUSEUM, REGISTER, JOURNAL, AND GAZETTE.

[merged small][merged small][merged small][merged small][graphic][ocr errors][ocr errors][ocr errors][ocr errors][subsumed][ocr errors][ocr errors][ocr errors][merged small][subsumed][subsumed][merged small][ocr errors][merged small][ocr errors][ocr errors][ocr errors][subsumed][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors]

PRACTICAL REMARKS ON AERIAL NAVI
GATION. BY SIR GEORGE CAYLEY,

BART.

Sir.-Permit me, through the pages of the Mechanics' Magazine, which widely circulates among the efficient mechanics of this engineering age, to call their áttention to a subject of great national interest, and one that offers perhaps the most difficult triumph of mechanical skill over the elements man has to deal with-I mean the application of aerial navigation to the purpose of voluntary conveyance. There seems to be, if we may judge by the scattered notices in the public journals, a revived attention to this subject, not only in this country, but also in France and America: the experiments that have been made, and the investigation which it has undergone, lie almost unconnected in the periodical publications of the last thirty years ; and hence every new speculator on the possibility of steering balloons, takes up the subject merely on his own view; and as it requires much complicated calculation, as well as the utmost exertion of engineering skill, it is not surprising that we do not make much progress, especially when we consider the enormous expense of making experiments upon it on an efficient scale of magnitude.

Among others, five-and-twenty years ago, I paid considerable attention to the subject of aerial havigation, and collected or ascertained several of the leading points and laws of action that must be complied with to render any attempt respecting it successful. These were pub lished in the Philosophical Magazine for 1816 and 1817, &c. I shail not, however, repeat much of what is there said, but proceed to state what I consider most conducive at present towards a final accomplishment of the aerial object in

view.

In the first place, the enormous bulk of balloons, as compared with the weight they will sustain, causes the difficulty of impelling them, with sufficient speed to be of any utility, either by manual or engine power; and this difficulty is by many

This letter was commenced about four months ago; I am extremely glad to see how much this subject has grown upon public attention since that time, and how many excellent notices of it are contained in the last three monthly numbers of

truly scientific persons considered as insurmountable, because they conceive that the bulk, which causes the resistance, must ever be commensurate with the weight of engine necessary to propel them by any species of waftage-and, consequently, as itwill not do on a small scale, that it can not on a large one. It is true, that it requires twice as much gas to sustain a 4-horse power engine as to sustain one of a 2-horse power (with their loads of fuel and water); but it is not true that the larger balloon, though perfectly similar in make to the smaller one, will, when driven through the air at the same velocity, meet with double the resistanceif it were so, the case of steering balloons would be hopeless, and on this mistaken ground many think it a vain attempt. This idea, resting at the very threshold of the invention, and which seems to present an insurmountable barrier, when probed and fully investigated proves to be false, and the investigation leads to an immutable law of proportion between the resistance and the capacity to carry weight or engine-power, which, satisfactory result. on a very large scale, promises the most

If balloons of the respective diameters of one and two, both being spherical, be driven through the air with equal speed, the resistance will be as the surfaces opposed to the air, and the surface of the largest will be four times greater than quire four times the engine force to keep that of the smaller, and hence it will reup the velocity; but the quantity of gas contained in the larger balloon is eight times greater than that in the smaller, hence it could sustain eight times as much engine-power; but four times that power would keep up the required velocity, and hence it could carry a cargo of the weight of its engine, and yet keep pace with the smaller balloon. The faces (and hence the resistances) increase simple terms of the case are, that the surloon; whereas the capacity to contain as the squares of the diameter of the balgas (and hence the supporting power) increases as the cubes of the diameter.

From this unquestionable law it follows, that if similar shaped balloons vary in diameter as the numerals, 1, 2, 3, 4, 5, &c., the resistance they will meet with in the air, at the same velocity, when com

your Magazine up to September, which I have just pared to the weight (or engine-power) they will sustain, will be as 1, 3, 1, 1,

received.

t, &c. This is a most important fact, and proves that as the law of relative di minution to resistance is unlimited, there must ever be, theoretically, some bulk in which any species of first mover, however sluggish in proportion to its weight, would find itself suspended, and its power adequate to propel that bulk with the velocity required. So far for the principles in action; let us now come to the real practical limits.and bearing of the case.

The first thing that presents itself to our notice is the choice of a proper ma terial of which to form a balloon for the required purpose; and the properties are those of being perfectly air-tight, light, and strong.

Silk and Indian-rubber

varnish are thus indicated, and have long been used; but in the larger constructions, that are suggested by the previous investigation, the expense of silk would almost prove a bar to real use.

The

double-cotton Indian-rubber cloth, used by Mr. Macintosh in his manufacture of air-tight seats and cushions of various kinds, weighs very nearly 1lb. per square yard, and will just sustain a tension of 2,500lbs. per lineal yard, that is, if the yard of cloth were rolled up and used like a rope, it would sustain any weight less than 2,500lbs. Of course, if used flat, as a portion of the surface of a balloon, it would sustain tension to the same amount. This cloth, when made to adhere to an adjoining breadth by an overlap of one inch with the Indian-rubber varnish, is air-tight at the seam; and is to the full as strong in resisting tension as at any other part, as I have found by experiments carefully made for the purpose.

As we now travel by railroad pretty constantly at the rate of 20 miles per hour, aerial navigation, though offering a direct navigable ocean to every point of our globe, would scarcely be worth cultivating, if not practicable ultimately at least up to that speed.

To be able to sustain the form of the balloon, when driven against the air with that velocity, implies that the condensation within must press rather more than the resistance of the external air; but at that velocity, by the well-known laws of resistance, every square yard near the centre, facing the line of flight, will meet a resistance of about 29lbs.; and hence the condensation over the whole interior of the halloon must give 29lbs. pressure

per square yard. More than this, balloons, to be really serviceable, must when at anchor, or by accident driven against obstacles, be able to resist the action of our most violent storms, which, according to Smeaton's table, go at the rate of 60 miles per hour, tearing up trees, and creating a pressure of 162lbs. per square yard.*

This cloth can just sustain 2,500lbs. per lineal yard; and hence, by calculating the forces, it follows that the extreme limit of size to which a spherical balloon made of it could safely be carried when occasionally condensed to meet our storms, whilst at anchor, or when compressed against objects casually by them, would be 60 yards in diameter.†

Let us not be startled at this deduction, for in practice we may use as much less as we find convenient; and it is a feature of very great importance in fa vour of aerial navigation, that such a slight fabric is capable of becoming a safe vehicle of support to so vast an extentand here it should be remarked, when balloons are made of forms differing from the sphere, that where for any considerable length they approach, as in elongated spheroids, to a cylindrical form, the cloth will only sustain near the minor axis half the pressure or condensation it will sustain as when in a sphere of the same

These calculations are based upon the resist ance being in the ratio of the squares of the velo cities; and that a velocity of 21 feet per second gives a resistance in air of Ilb. to the square foot.

The whole lineal measure of the circumference (being, in round numbers, 188 yards, capable of bearing 2,500lbs. each), can bear 470,000lbs.; whereas the whole area of the great circle on which the pressure takes place, being 2,840 square yards with a pressure of 162lbs. on each, only amounts to 460,000lbs.

In speaking of condensing the gas in balloons, which is a new feature in them, it will be necessary to provide a safety outlet by bringing a wide pipe from them, and placing the end of it a few inches under water; a column of 3 inches of water would equal the condensation of 162lbs. per square yard. The escape of gas should be into a small empty balloon above the water, from which it can be pumped out at pleasure; the change of temperature in the climate also requires this structure. Eventually balloons will probably have a double casing, with common air, or, what would be safer, azote, pumped in between them. A small balloon to contain common air pumped into it, having a tube from it with its mouth a certain number of inches under water, and its bulk contained within the gas-balloon, would be the readiest way to meet all cases of condensation and expansion. With air-tight materials there would be no mixture of comon air with the hydrogen, but this plan would require the materials to be perfectly so. To prevent danger from the fire of the engine, several wire-gauze divisions should be made in the chimney.

diameter; hence 30 yards would be the extreme limit of the shorter axis of an elongated spheroidal balloon made of this cloth.

As the netting, belting, or whatever means be adopted to enable the floatingpower of balloons to sustain the burthens attached to thein, must necessarily extend over more than half their surface, it would be best to complete the circuit, and thus add the strength of the netting to resist condensation, and fortify the cloth, especially near the shorter axis.

Condensation is a term that seems, and to a certain extent is, adverse to aerial navigation; but the whole condensation here required will only deduct 1lb. of buoyancy from every 120lbs. previously exerted by the gas, a sum too trifling to be of any consequence, and abundantly redeemed by the firmness it gives to whatever form it may be required to model balloons for obviating as much as possible the resistance of the air.*

The next consideration is the proper form of the balloon for this purpose; and here it is obvious, that to extend their length horizontally, and thus to diminish their cross-section, is the leading point of the investigation. This will be limited by the practicable extent to which the structure can be carried without incurring weakness, in respect to the preservation of form, or inconvenience in the mode of suspending the car or body from the baltoon. Ships and boats range between three and six times the measure of their greatest cross-section; birds between two and four. When convenience has pointed out the limits that must guide us in making use of length to obviate resistance, the form of the balloon, to meet the least resistance within these limits, is naturally the next inquiry. Unfortumately even the sagacity of Newton has not been able practically to grapple with this very interesting and intricate question; and his beautiful theorem on this subject will not apply to any of our gross fluids, which wedge themselves up by accumulation after they have struck upon the resisting body, and have no free egress to make room for others. The New

The expense of using pure hydrogen gas poin's out the necessity of balloons being perfectly airtight, and when used as permanent vehicles, and on the true scale of magnitude, they will probably be made of thin metallic-heets kept firm by con densation, with separate light bags of gas within.

tonian solid of least resistance has a prow concave near the anterior axis; and as air is more elastic than water, the prow, if we may use the term, of birds is also concave; whereas in fishes the prow, as in ships, is convex. In the absence of all good authority, I have proposed (at p. 400 of the Philosophical Journal for 1816) to copy the prow of the woodcock as there given by exact measurement. This bird was selected from its having frequently to pass 500 miles of sea at one flight; and because in its structure Nature seems to have united every contrivance to blend strength with lightness. The resistance of the air to its passage was the great obstacle to be overcome; and hence it is more than probable the best form (which, more than all the rest, would tend to the ease of the performance) has been selected also. It is about 3 times the length of its greatest crosssection.

The hinder portion of resisting solids is proved by experiment to be of as much importance as the prow; but as its office is to fill up the space, shielded from pressure for a time by the diverging momentum of the fluid driven off by the prow, any figure approaching to that of the cone answers the purpose tolerably well, if we may judge by the lengthened conical taper of the tails of fish; indeed it is a common expression among sailors, that a ship to sail well should have a "cod's head and a mackerel's tail."

We may rest contented to make our experimental balloon of an extended spheroidal form, and leave the rest to future improvement. The best form of ships remains in a great measure to be ascertained yet; although navigation has been bestowing wealth and comfort on mankind for so many ages under a rude approximation to it.

The next objects of inquiry are the power to be used in propelling the balloon, and the means of applying that power. Only two general modes have, I believe, ever been proposed by competent persons for this purpose. My friend Mr. Evans (see the Philosophical Magazine, for 1815, vol. xlvi., p. 321,) tried with success to steer a small Montgolfier balloon by suspending a large oblique surface beneath it, which caused the ascent to be oblique in the direction towards which the upper edge of the plain was pointed; when the fuel failed, gravita

« iepriekšējāTurpināt »