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 hot, 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 in VOL. 11.-No. III. 28 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, in"dicates 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 Sixed 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. 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 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 possible, 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 drawe 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 inte 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 two 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 (II.) 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 operation 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 engine, without intermission, and that according to the number of the teeth on both sides of the frame, so will be the number of strokes the plungers will make during the period of each stroke of the engine. It will, therefore, be easily perceived that by this simple movement, we may increase the velocity of the plungers at pleasure; and that from their situation, we may increase their perpendicular surfaces in proportion to the power of the engine. consequence of this new arrangement was, that when the plungers were forced down, the valves under each were closed, and also the valve in the bottom of each lateral trunk, while the valve immediately above it was opened, and permitted the water under the plungers to enter, causing the water in the lateral pipes to run out at their upper extremity, and pass over contractors to the sides of the vessel, where it was discharged. When the plungers were drawn up, the water which A considerable quantity of cold water had, during the previous operation, been being required to absorb the heat con- forced over the tops of the open lateral tained in the rarified air in the contrac- trunks into the trunks of the plungers, tors, I was led to think of some method was lifted to the surface, and passing also of obtaining it from under the boat, and over the contractors, was discharged in a with as little expense of power as possi- similar manner-in the mean time the ble. On reviewing the operations of the valves were opened and the trunks filled, plungers in motion, I perceived that a when the same operation was succeeded part of the reaction of the water on the by the same effects, as long as the plunstern was lost, being spent in pursuing gers were actuated by the cranks of the the plungers in their returning motion;- shaft, which is connected with the piston to prevent this, I placed a valve in the en- rod of the engine. The effects produced trance of the inclined part of each of the by the vacuum thus obtained were obtrunks, and furnished the plungers with vious-the water at the stern being exvalves so constructed as to operate on the cluded from entering the trunks by the principle of a lifting and forcing pump;- valves placed at the commencement of its the consequence was that I obtained a inclined part now entered altogether at supply of water from the forward part of the other extremity of the trunks at the the boat, and the water under the stern, bows of the boat-this was precisely the instead of pursuing the plungers as here- effect I had anticipated, together with the tofore, was prevented by the valves in the spontaneous movement of the boat in a trunks on which the water now reacted. forward direction, the natural result of By this method of operating, I soon dis- the operations of the pressure of the atcovered, that I had not only brought into_mosphere and the lateral pressure of the the boat a considerable quantity of water for the use of the contractors, without loss of power, but had relieved the forward part of the boat from a part of the resistance it sustained from the pressure of the incumbent water. Hence the application of a valve in each trunk is all-important, and distinguishes this application from all others of a similar nature that have not succeeded merely from a want thereof. A little reflection induced me to see how far I could improve this effect by making a more perfect vacuum under the boat. With this intention I removed all the trunks and plungers, except two, leaving one at each side of the vesselthe plungers in these two were then placed in a perpendicular position, and had united to their trunks a similar trunk placed on each side-the valves were now taken from the plungers and they were fitted to work air-tight-a valve was placed in the bottom of each trunk of the plungers-one of the lateral trunks left entirely open, the other furnished with two valves at the extremity connected with the submerse-trunk. The water against the stern and sides of the vessel-while it was excluded from the bows by the removal of the water from that part into the vessel, by the operation of the pumps. Hence a new and impor tant application of power, which will be in proportion to the power expended by the engine in raising the water. The quantity of water raised will be in proportion to the surfaces of the pistons, and the respective heights to which it may be raised, the velocity of the boat will be in proportion to the motion of the pistons, which may be increased at pleasure. It then became a matter of calculation to ascertain whether the pressure thus obtained was equivalent to the force of the engine as applied in the first instance-and I was satisfied that this new mode of application, combined in less compass, all the advantages of the former in a more perfect degree. After carefully reviewing this operation, it occurred to me that the arrangement was susceptible of further improvement-there would be convenience in reversing the motion of the boat, and also in suspending the effects of the operating power. To effect these objects, a pair of upright sliding valves, with lifting rods attached to them, were placed in each submersed trunk, near the centre, on each side of the perpendicular trunks. When both of these valves are raised or pushed down, the motion of ths boat is suspended. When the boat is in motion in any direction, one valve is up while the other is down-and when it is required to reverse the motion of the boat, the operation of the valve is also reversed. This arrangement suggested the idea of furnishing the trough of the inclined wheel with valves for the purpose of producing the effect of the vacuum thus obtained, though in an imperfect degree. With this intention a perpendicular valve with a lifting-rod attached to it, was placed in the trunk, on each side of the wheel, for the purpose of altering or suspending the motion of the boat, &c. The effects produced by these valves were new and surprising. When the water-wheel is put in motion, it removes the water out of the trunk, or trough part of it, which is under the wheel; while this operation is going on, the pressure of the atmosphere and the gravity of the water are partially removed from the forward to the after part of the trunk operating on the valve behind the wheel, which is down while the other is up. Hence the boat advances forward, and the trunk is supplied with water, which is resisted partially by the entering paddles, and, in proportion, assists the wheel in its progress, while the water thrown out contributes to increase the effects of the pressure of the atmosphere and the gravity of the water. Hence according to the velocity of the wheel so will be the quantity of the water displaced, and the vessel will advance in proportion. The application of this principle is new and interesting, and, though greatly inferior to the other indirect applications, will be attended with many advantages. It remains to give a description of the peculiar form and construction of the boat alluded to in the preceding remarks, which I have denominated an Air Boat, accompanied with necessary explanations. Description of the Air Boat. A vessel ought to be constructed so as to answer the particular purpose for which she is intended. When she is intended to sail by means of mechanical force, her form should be different, because when sails are used, she is then acted upon by two elements, the wind and water, and requires a greater degree of stability to be able to carry a press of sail,-considerable depth in the hold for the cargo, long keel, and little breadth to prevent her falling to leeward. When she is to sail by mechanical force, her form and size should be very different. For this purpose the bottom should be formed quite flat, (to sail as much as possible on the water,) and the sides made to rise perpendicular from it, without any curvature; which would not only render her more steady, as being more opposed to the water in rolling, but likewise more convenient, accommodating, &c. while the simplicity of her form would contribute greatly to the ease and expedition and economy with which she might be fabricated. Diminishing the draft of water is undoubtedly the most effectual method of augmenting the velocity of the vessel, but as it proportionably diminishes her hold of the water, and renders her more liable to be driven to leeward, this defect is remedied by the trunks under her bottom, which are an excellent substitute for a keel. By means of these side trunks she will be kept steady in the greatest gale, quite easy in a great sea, will not strain in the least, and never take in water on her deck; and when at anchor, will ride more upright and even than any other vessel can do. Her extreme breadth should be no more than the 5th or 6th part of her length: her bows a little curved to break the force of the water, and her stern something narrower than the bows, having a gentle in clination from the stem to the stern, to promote the action of the atmosphere and the water on the sides. I I think in the preceding remarks that have established the following facts: 1st. That the power of atmospherical air and fixed air, increased by condensation and heat, as digested and arranged by me, is not only a very great, but the most eligible and most powerful agent for mechanical purposes. 2d. That in applying this power, a circular engine, on my construction, is the most useful of any other: and that by the simple escapement of the piston-rod of the steam engine, I have given it an advantage in reciprocating movements it had not before. 3d. That in the present steam-boat system there is an aggregate loss of nearly three-fourths of the power of the engine: and that on my plan the whole force of the engine can be applied without diminution, and with the one-fiftieth part of the fuel usually consumed in the present method. Hence my method of applying the |