The following article has been called forth by the appearance of Mr. Busby's "Essay on the Propulsion of Navigable Bodies," and the account of his discoveries and inventions, published in our last number. Mr. Busby and Mr. Staples are, we believe, total strangers to each other; it has, however, been supposed, by the friends of the latter, that the modes of propulsion suggested by these gentlemen interfere. We, nevertheless, submit that the two plans differ, in essential points; but, recommending an attentive consideration of their respective merits, we leave our readers to determine which should obtain the preference.

AIR BOAT. MESSRS. EDITORS,

As one of the objects of your useful Magazine is to disseminate the knowledge of new inventions and improvements,-I avail myself of that medium to lay before the public the result of a course of experiments in mechanical science, and particularly as applied to navigation.

A variety of untoward circumstances have combined to prevent an earlier developement of all the facts now deduced; but the time seems to have arrived when I should no longer remain silent.-In giving this to the public I do not arrogate to myself the discovery of any new principle in mechanical or chemical philosophy, but I lay claim, with perfect confidence, to all the advantages that may arise from a new and practically useful application of long known principles.

The science of mechanics, very early engaged my attention; and I happened to be in England at the time that Bolton and Watt had perfected the steam-engine, and was then indulged with an opportunity of witnessing its useful effects in their extensive manufactories. I saw the same engine afterwards tried by Mr. Fitch for propelling vessels on the Delaware, and by many others in different places, and lastly by Mr. Fulton, who, being satisfied with the engine, considered only the best method of applying its powers to navigation, although it is very apparent he did not select the most elegible appendages to give that engine all its adtages of propulsion.

which they were moving, the other half being spent in efforts tending to elevate the boat, occasioned a reaction, which oppressed the machinery, and caused a constant vibration of the vessel-hence a loss of power by the increased friction, in addition to that sustained by the perpendicular action of the paddles, both in entering and leaving the water. But the leaving paddles has even a worse effect, by breaking the volume of water on which the pursuing paddle is required to act in its nearest approach to a horizontal line; and this is an objection that will apply to wheels of every description. Stimulated by a desire to correct these evils, I have, from that time, been occasionally engaged in a succession of experiments-one inducing another, one idea unfolding another in regular progression, until I have attained the climax of my wishes-an economical application of known principles to useful purposes.

When the first boat was started from New-York, I took passage with a view to witness the experiment; and then noticed the great loss of power in the use of wheels-I saw that the paddles entered and left the water at an angle of about 45° and when entering, could only exert on its surface about half of the power with

Prior to the period alluded to, I was engaged in experiments on the tide wheel, with a view to relieve them from the resistance of back water, and succeeded in the attempt, by using upright paddles ; and when the objections to the common wheel, as applied to boats, were so evident, it appeared to me that the applica tion of what I term the improved wheel would be very useful. But the trouble and expense of its construction; the difficulty of repairing any injury, except by a skilful artist; and the extreme accuracy ne cessary in its structure to take off some of the immense friction inseparable from such a combination of parts, determined me to relinquish that, and substitute a solid wheel, somewhat similar to the one in common use, but with a less number of floats, to prevent as far as possible the breaking of the volume of water unneces sarily; and placed in an inclined instead of a verticle position, enclosed in a horizontal trunk open at each end. There were too objects expected from the use of the trunk-one to gain buoyancy by extending the surface and preventing, as far as possible, the unequal operation-of the wheels, in rough water; the other, to confine the water about the wheel, and make it approximate as nearly as possible to a solid substance. I had no sooner effected this, than my attention was called to examine a circular engine on a new construction, just then made known to me, being anxious to witness the result of experiments then going on in NewYork, because I had already been engaged for some time in similar trials; but when I found that steam was the only

agent, and its reaction could not be overcome, I felt under no apprehensions as to an interference in my plans. My circular engine is, I believe, entirely free from the defects common to all others that I have any knowledge of, being a horizontal movement, and actuated by an elastic, or a non-elastic fluid, or both; and in the latter case the engine is occupied with hot water, which is interposed, because it lessens the necessity of tight packing, and does not diminish the operating force of the engine by any reaction, which cannot be so well prevented in the use of elastic fluids only. Such, however, were the prejudices against circular engines, occasioned by recent unsuccessful applications, that I judged it prudent to suspend the introduction until I could accompany it with other improvements connected with its operation. My attention was now turned to an article inserted in the newspapers from an English publication, stating that a gentleman had obtained a patent in London for the application of condensed air as a new power to propel vessels, by injecting it under the bottom, thus causing a reaction of the water in its escape to the surface, by expansion on a part of the bottom inclined for that purpose. This article was followed by two others, the one from Boston, and the other from Philadelphia, each claiming a priority of application. Similar matters had engaged my attention, but I went further than they did. They found that nothing was to be gained by this application of force, sufficient to compensate for the loss of power in obtaining it-in my application I used heat as an auxiliary, having previously discovered that air will expand in proportion to its density with the same degree of heat. This matter will be more fully noticed when speaking of the engine and appendages asat present arranged. To obviate the difficulties attaching to all wheels as before noticed, I tried the effects of simple instruments, operating on the water under the stern of a vessel, on the principle of an oar, and found them preferable to the paddles or floats of a wheel; but their progress in the water not being in the line of the boat's direction, I constructed a pair of parallel oars -these operated admirably, with the exception of a slight resistance on entering and leaving the water.

Although it was very evident, that vast power was to be obtained by condensed air rarified; yet, separate from other objections, the use of it, as before noticed, was not desirable on the score of economy. Hence I was led to think of a dif

ferent application under the vessel, and with this view I found it necessary to have its bottom flat, with the part near the stern inclined upwards. I then contrived a set of plungers, which were to operate in trunks passing through the bottom of the vessel near the sides, on an angle of about 45o, rising in the vessel about three feet above the bottom, and connected with similar trunks under the bottom, extending from one extremity of the vessel to the other, and also attached to its inclined part, rising to the surface of the water under the stern of the vessel. having a portion of that inclined part, near the extremity of the trunk, removed for the purpose of producing a reaction of the water on it. The piston rods of these plungers are connected with the cranks on the main shaft in pairs, the cranks being so arranged as to distribute the power in an equable manner. There are three pairs-the two outside plungers moving together, the others succeeding in the same order. The surface of the plungers, when in contact with the water, is perpendicular, and if necessary may occupy the whole breadth of the vessel-hence the surfaces of the plungers may be made to bear on a section or column of water vastly greater than can conveniently be allowed for the action of any wheel or oar. Although these plungers will be more firmly resisted by the water than the oars or paddles of wheels possibly can be, yet by the yielding of the water, some little suspension of power will ensue; but by its immediate reaction on the inclined part of the bottom, it will be restored.

Having now satisfied myself with arranging the instruments to operate on the water, I resumed my experiments on air for the purpose of ascertaining the best methods of combining in practice its greatest economy with convenience; and considered, as connected with its application, the properties of heat, and the capacities of bodies for retaining heat-and my conclusions are drawn from the following statement of experimental facts:-

Of all the compressible fluids, air is the most familiar-hence it will not be necessary to give an elementary account of its distinguishing properties, further than is requisite to elucidate the theory I am going to advance. It is a well known fact that air is a compressible and dilatable body-that it is always in a state of compression-that it is an elastic fluið whose density is always proportionable to the compressing force-that its elasticity is proportionate to its density, and that it will expand in proportion to its

density; but it is not so well known that this expansion will be effected by the same degree of heat. The result of experiment had assured me of this fact, when I noticed in the Encylopedia Brittanica that AMONTON had expressed the same idea.

bore, because the pressure against every square inch is 15 pounds, and, therefore, against every circular inch about 12 pounds. If the condensor be one inch diameter when one atmosphere is injected, there will be a resistance of 12 pounds against the piston; and when ten atmospheres are injected, there will be a force of 120 to overcome; and as the facility of working will be inversely as the squares of the diameter of the condensor, it will be proper to have them of various sizes, and to begin with those of a larger diameter, which operate more quickly; and when the resistance against the piston is nearly equal to the force employed, to change the condensor for one of a smaller bore. We judge of the condensat en or compression of the air in the receiver by the number of strokes, and the proportion of the capacity of the condensor to the receiver. Suppose the first to be one-tenth of the last, then we know that after ten strokes, the quantity of air in the receiver is doubled, and, therefore, its density double, and so on after any number of strokes. When any great power is employed, the condensation may be pushed to a great length. By condensation the quantity of absolute or specific heat in air is lessened, being pressed out through the pores of the metal, by which means the air is rendered more dense, compact, and heavy, and its capacity for receiving heat is increased. By heat all bodies are expanded every way, and that in proportion to their bulk and the quantity of heat communicated to them. The expansion takes place not only by an addition of sensible heat, but likewise of that which is latent; an instance of this expansive power of latent heat is found in steam, which always occupies a much larger space than the substance from which it was produced. All the experiments hitherto made conspire to show that the capacity and consequently the specific heat, is greater in the vaporous, less in the fluid, and least in the solid state. Many experiments have been made to ascertain the capacities of bodies for containing heat, and also the quantity of absolute heat contained in different bodies-the temperature, the capacity for containing heat, and the absolute heat contained, are distinguished as a source distinct from the subject upon which it operates. "When we speak," says Dr. Crawford," of the capacity, we mean a power inherent in the heated body; when we speak of the absolute heat, we mean an unknown principle which is retained in the body

It has been found by many experiments that air is of different constitutions-below it is warm, loaded with vapour, and very expansible; above it is cold, much drier, and less expansible, both by its dryness and its rarity-moist air expands most by heat-rare air expands less than what is drier. Rarified air differs in nothing from common air, except that it is lighter, and contains more heat. Condensed air is heavier than common air, and contains less heat. The elasticity of air is greatly affected by heat, and the change by increase of temperature is different, according to its density or compression. In common with water and other fluids, air possesses gravity; and consequently will perform every thing in that way which water can do, making allowance for the difference between the specific gravities of each-air being 840 times lighter than water. There is another property which it has in common with steam or vapour: this is called its elasticity, by which, like a spring, it allows itself to be compressed into smaller bulk, and then returns again to its original size, upon removing the pressure. It has been so compressed as to take up but the 1000th part of the space it occupied before, and of course its density in that state being one thousand times greater than the air we breathe. In every state of density it has been found to retain its perfect fluidity, transmitting all pressures which are applied to it with undiminished force. The dilation of air by its elastic force, is found to be very surprising; it has been brought to dilate into 13,679 times its space, and this altogether with out the help of fire; and this property of elasticity is as the density of the air.

By means of a suitable condensor, which may be actuated by any eligible power, an uncommon quantity of air may be crowded into a given space, so that without impairing its spring, 1000 atmospheres, or 1000 times as much air as there was at the same time in the same place without the instrument, may, by means of it, be thrown into a suitable vessel denominated a "Receiver," and its egress prevented by valves suitably disposed. In order to condense air to a very great degree, it will be requisite to have the condensor of a small

by the operation of this power; and when we speak of the temperature, we consider the unknown principle as producing certain effects upon the thermometer."These different powers are called the capacities for containing heat::-"thus, if we find (continues the Doctor,) by experiment, that a pound of water contains four times as much absolute heat as diaphoretic antimony when at the same temperature, the capacity of water for containing heat, is said to be to that of antimony as 4 to 1;-again, thus the quanti ty of absolute heat in two pounds of water, is double that which is contained in one pound when at the same temperature, because the quantity of absolute heat will be proportionate to the bulk of the matter." A quantity of air heated to such a degree as is sufficient to raise Fahrenheit's thermometer to 212°, will occupy a considerable space. If cooled to such a degree as to sink the thermometer to 0, it will shrink into less than half its former bulk. The quantity of repulsive power, therefore, acquired by air, while passing from one of these states to the other, is evidently owing to the heat added to or taken from it. A cubic foot of common 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 1-500th part of the whole. By heating a quantity of air, therefore, to 500° of Fahrenheit, we will just double its bulk when the thermometer stands at 54° in the open air, and in the same proportion we diminish its weight. The quantity of caloric or heat, necessary to increase the bulk of 1000 parts of atmospheric air to 1027, will increase the same bulk of steam to 1032-water to 1050, and fixed air or carbonic acid gas to 2345, an immense difference in favour of the latter.

to a small space as effectually as by mechanical pressure. Hence the office and structure of the contractors, to be presently described. Fixed air, or carbonic acid gas, is a permanently elastic fluid, and like all others, is formed of a terrestial substance. It has the same mechanical properties with common air, viz. that of occupying a space inversely proportioned to the weights with which they are pressed. The weight of this gas, indicates that it contains a considerable portion of aqueous matter; and it is by means of this constituent principle that it is

miscible with water. Its weight in all circumstances of pressure, is to that of common air very nearly as three to two; hence its specific gravity will be about 001806, and the weight of a cubic inch at 60° thermometer, and 295 inch barometer, will be about 456 of a grain. It is the hea viest of all known gases, except the sulphu rous. From a suite of well conducted and laborious experiments, Dr. Crawford found, that as much heat as would raise the temperature of atmospheric air one degree, would raise fixed air 67. From Mr. Robin's experiments on gun-powder, (which is a composition of salt-petre, sulphur, and charcoal,) it appears that in firing of gunpowder about 3-10ths of its substance is converted by the sudden inflammation into a permanently elastic fluid, whose elasticity in proportion to its heat and density, is the same with that of common air in the like circumstances; it further appears, that all the force exerted by gunpowder in its most violent operations, is no more than the action of the elasticity of the fluid thus generated.

The velocity of gun-powder is 1700 feet in a second. The pressure exerted by fixed gun-powder before it dilates itself, is more than 1000 times greater than the pressure of the atmosphere, and consequently, the quantity of force, on the surface of an inch square, amounts to about six ton weight; which force, however, diminishes as the fluid dilates itself. An ounce of gun-powder will produce near 460 cubic inches of this elastic fluid. It may be collected from hence, and other circumstances connected therewith, that the permanently elastic fluid mentioned by Mr. R. is no other than fixed air; because the effects are analogous to those related by Dr. Crawford in his experiments on heat, fixed air, &c.

Mr. Robins supposes that the heat with which the flame of gun-powder is endowed, to be the same with that of the extreme heat of red hot iron 1085. The most probable opinion concerning the ex

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plosive properties of pulvis fulminans, is, that fixed air contained in alkali, is by the acid vapours acting upon, and endeavouring to expel it, all at once driven off with such force, that a loud explosion is produced. It has been supposed by some very eminent chemists, among whom, we may number Dr. Black, that fixed air is the cause of the fulmination of gold. And it appears from equal authority that the stronger the spirit of nitre is, the more it is expanded by the same degree of heat. And as the dilation of the spirit of nitre is far greater than that of water by the same degree of heat, and as it consists only of acid and water; it clearly follows, that its superior dilatability must be owing to the acid part; and hence, the more acid that is contained in any quantity of spirit of nitre, the greater is its dilatability.

This fact will perhaps appear in a clearer light from the experiments of Mr. Ro bins on gun-powder, and opinions of the most learned and eminent chemists, respecting the cause of the explosive pro perties of fulminating powders, and the properties of acids, they all point to fixed air as the cause of all these surprising phenomena. Hence fixed air when rarified to 1050, is as powerful as gun-powder under similar circumstances, and when rarified in small quantities may be with perfect safety applied to actuate an engine precisely as steam, in the manner to be described. In applying the mechanical properties of rarified condensed air, and rarified fixed air, so obtained, to mechanical navigation, I purpose employing either my circular engine, or the steam engine so modified as to be actua ted in such a manner as to admit of its power being transmitted with as little diminution as possible to the instruments, I have contrived to connect it with the water for the purpose of moving the boat with a velocity equal to the whole force of the engine; which hitherto has been deemed impracticable. It will easily be perceived that to effect this object, 2 peculiar train of means must be employed.

Instead therefore, of the bulky boiler and its apparatus, a cylindrical vessel of the size of the cylinder of the engine, denominated a "receiver," E. and two flat shallow cast iron vessels, denominated "rarifiers," of a capacity equal to the "receiver," are to be substituted, with a very small furnace. A pair of flat shallow vessels denominated "contractors," F. F. supply the place of the condensing appaAnd in the place of water-wheels ratus. plungers are employed, except in one instance, where the common water-wheel, with less floats than usual, is so circumstanced, as to admit of its application with diminished inconvenience in the manner already described.

The limits prescribed for this article.