agent, and its reaction could not be overcome, I felt under no apprehensions as 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 45°, 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 capaci, ties 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 fluid whose density is always proportionable to the compressing force that its clasticity 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.

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 without 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

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

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.

It is a well known fact that aerial fluids acquire heat with great celerity, and expand with immense velocity, when affected by it to any considerable degree; and from innumerable observations, it may be laid down as an undoubted fact, that there is no substance whatever capable of being reduced into a state of vapour, but what in that state is endowed with an elastic force ultimately superior to any obstacle we can throw in its way. When .air is violently compressed, it becomes bot, by reason of the quantity of a more subtle element squeezed out from among the particles. By diminishing the heat of any quantity of air, its elasticity is effectually diminished, and it will shrink inVOL. -No. 111.

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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 heaviest of all known gases, except the sulphurous. 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

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 singular effect is one of the distinguished properties of acids, whose capacities for heat are very small;-hence 'the small capacity of fixed air, or carbonic acid gas for heat, is owing to the acid part of this fluid, and from the quantity of fixed air in charcoal, and also from what is contained in the sulphur and salt-petre of which gun-powder is composed, it is evident that the elastic fluid extricated by the chemical solution of these substances is principally fixed

air.

From the preceding statement of experimental facts, and the subsequent calculations founded thereon it must be evident,

1. That it requires more heat to raise the temperature of common or atmospheric air, in its usual state of compression, than it does steam. Hence no advantage can be derived from its application in that way.

2. That no more power can be obtained from the spring and weight of the air, increased by condensation, than is employed in its compression, unless it is rarified by

heat.

3. That the advantage to be derived from rarifying compressed air, will be in a ratio proportioned to the number of atmospheres that are rarified by the same degree of heat. Hence the power will be in proportion to the capacity of the engine; and the advantages to be derived will consist in using a more economical and less bulky apparatus, and in the consumption of less fuel than by the usual methods.

4. That the same heat which raises atmospherical air one degree, will raise fixed air nearly 67 degrees, and conse.

quently, that the same heat which raises atmospherical air any given number of degrees will raise fixed air the same number of degrees multiplied by 67. Hence fixed air is a more economical power than condensed air rarified.

5. That the same heat which increases the bulk of 1000 parts of water, to 1050, and steam 1032, increases the bulk of fixed air 2345. Hence fixed air is a more economical power than steam, not requiring the 1-50th part of the fuel requisite to generate steam, to produce the same effect.

This fact will perhaps appear in a clearer light from the experiments of Mr. Robins on gun-powder, and opinions of the most learned and eminent chemists, respecting the cause of the explosive properties 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 actuated 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, a 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 apparatus. And in the place of water-wheels, 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,

and the short notice for its insertion, makes it necessary that the description should be compressed in as small a compass as possible; and as the operations of the steam engine have become familiar, I purpose exhibiting this engine in an appropriate representation prefixed to this article, in which it will appear as connected with my improvements, instead of my circular engine, which will be more fully described in a work I purpose publishing, which will embrace the whole system and the advantages to be derived from its application to all kinds of mechanical purposes where motion and force are required, and especially to the propulsion of navigable bodies. We have seen that the application of steam is cheaper than that of common air rarified; that rarified condensed air is less expensive than steam; and that rarified fixed air is more economical than rarified condensed air. Hence I purpose employing that agent, especially in long passages. Fixed air may readily be obtained, and at a small expense. When the engine is to be actuated by fixed air, the vessel in which it is contained is to be connected with the "receiver;" and when the communication is open, the superior gravity of the fixed air causes it to enter the "receiver," and displace the atmospheric air contained therein. The communication between the receiver and the rarifiers being also open, the fixed air also takes the place of the common air in those vessels. During this operation, the communication between the rarifiers and the engine are shut. The attention of the engineer is now directed to the air pump, connected with the receiver and also with the engine, through the medium of the contractors, by suitable conducting pipes, for the purpose of exhausting the common air out of these vessels. When this operation is performed, the communication between one of the rarifiers and the engine is opened: the heated air then rushes out on the piston, which is propelled by its expansion; this operation gives motion to the main condensing or air pump; hence the expanded air is drawn out of the cylinder of the engine into the contractor, which is so situated at the side of the boat as to be completely immersed in a quantity of cold water, that is constantly thrown on it, and discharged at the side of the boat. Now it is an axiom that heat decreases as it recedes from the source from which it sprung; being absorbed by the surrounding bodies, until they are brought to an equilibrium. Hence, as the heated air is extended in

the contractors in as thin a sheet as pos sible, and as the motion of the water is rapid and continual over the whole exterior surface of the contractor; it follows that absorption must be rapidly carried on; by which means the heat is drawn out of the included air, and it shrinks into a small compass as effectually as by mechanical pressure: in this contracted state, it is forced into the "receiver" by the condensing pump, in the mean time, the heated air in the other rarifier is expanding on the piston, causing it to descend: it is then drawn out of the cylinder of the engine, by the operation of the condensing pump, and passes through its "contractor," when the same operation is repeated as in the first instance; and the contracted air returned to the "receiver," in a state of density similar to the air included therein. From the "receiver" it is injected into the “rarifier,” E. by a small powerful pump, operating upon the hydrostatic principle, and so on.

Thus by the alternate expansion and contraction of the same quantity of fixed air, which is not expended, a continued motion is produced. The motion of the engine is communicated to the plungers that operate on the water, by means of an escapement (H) which I have contrived for that purpose. The upper part of the piston-rod of the engine, consists of twe strong parallel bars, connected together, as at H. H. having teeth in their sides which front each other. The shafts (to which the piston-rods &c. are attached, by means of cranks projecting fron it) is placed between, having firmly attached to its centre part a short cross bar (H.) or pallet, calculated to be operated upon by the teeth of the rack. The teeth are so disposed, that after a tooth on one side of the frame has raised one end of the pallet and is leaving it, a corresponding tooth on the other side is coming in contact with the depressed or opposite end of the pallet, and raises it in a similar manner, and so on in succession,-the same ope. ration being repeated in the reverse motion of the frame. The uppermost tooth on one side, and the lowest on the other, are both a little longer than the others, and form the escapement; and are for that purpose, moveable in sockets regulated by springs, to permit the last tooth to react on the pallet it had just left. It is evident, without any further description, that this cross bar or pallet must be moved alternately up and down by each succeeding tooth, both in the upward and downward motion of the piston rod of the