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It has four cylinders. Two, of seventy-two inches in diameter, stand side by side. Over each of these is placed one much smaller. Within these are pistons, exactly fitting their respective cylinders, and so connected that those within the lower and upper cylinders move together. Under the bottom of each of the lower cylinders a fire is applied. No other furnaces are employed. Neither boilers nor water are used. The lower is called the working cylinder ; the upper the supply cylinder. As the piston in the supply cylinder moves down, valves placed in its top open, and it becomes filled with cold air. As the piston rises within it, these valves close, and the air within, unable to escape as it came, passes through another set of valves, into a receiver, from whence it is to pass into the working cylinder, to force

up the working piston within it. As it leaves the receiver to perform this duty, it passes through what is called the regenerator, which we shall soun explain, where it becomes heated to about four hundred and fifty degrees, and upon entering the working cylinder, it is further heated by the fire underneath. We have said the working cylinder is much larger in diameter than the supply cylinder. Let us, for the sake of illustration merely, suppose it to contain double the area. The cold air which entered the upper cylinder will, therefore, but half fill the lower one. In the course of its passage to the latter, however, we have said that it passes through a regenerator, and let us suppose, that as it enters the working cylinder, it has become heated to about four hundred and eighty degrees. At this temperature, atmospheric air expands to double its volume. The same atmospheric air, therefore, which was contained within the supply cylinder, is now eapable of filling one of twice its size. With this enlarged capacity, it enters the working cylinder.

We will further suppose the area of the piston within this cylinder to contain a thousand square inches, and the area of the piston in the sup ply cylinder above, to contain but five hundred. The air presses upon

this with a mean force, we will suppose, of about eleven pounds to each square inch ; or in other words, with a weight of 5,500 pounds. Upon the surface of the lower piston, the heated air is

, however, pressing upwards with a like force

upon each of its one thousand square inches; or in other words, with a force of 11,000 pounds. Here, then, is a force which, after overcoming the weight above, leaves a surplus of 5,500 pounds, if we make no allowance for friction. This surplus furnishes the working power of the engine. It will be readily seen that after one stroke of its pistons is made, it will continue to work with this force, so long as sufficient heat is supplied to expand the air in the working cylinder to the extent stated; for so long as the area of the lower piston is greater than that of the upper, and a like pressure is upon every square inch of each, so long will the greater piston push forward the smaller, as a two-pound weight upon one end of a balance will be quite sure to bear down one pound placed upon the other. We need hardly say that after the air in the working cylinder has forced up the piston within it, a valve opens, and as it passes out, the pistons, by foree of gravity, descend, and cold air again rushes into, and fills the supply cylinder, as we have before described. In this manner the two cylinders are alternately supplied and discharged, causing the pistons in each to play up and down, substantially as they do in the steam-engine.

We trust our readers will be able, from the brief description we have here attempted, to understand at least the general principles upon which this machine operates. Its cylinders draw their supply from the atmosphere. The cylinders of the steam-engine are supplied by scalding vapor, drawn from hissing boilers. The caloric engine draws into its iron lungs, the same element which expands those of the must delicate child, and derives its motion and its power from that sustaining source upon which depends the existence of all animate life.

We have endeavored to explain the construction of the caloric engine. Its most striking feature consists in what is called by its inventor, the regenerator. Before describing this, we will present the grand idea upon which it is based. First let it be remembered that the power of the steamengine depends upon the heat employed to produce steam within its boilers. It will be seen that from the very nature of steam the heat required to produce it, amounting to about 1,200°, is entirely lost by condensation the moment it has once exerted its force upon the piston. If, instead of being so lost, all the heat used in creating the steam employed could, at the moment of condensation, be reconveyed to the furnace, there again to aid in producing steam in the boilers, but a very little fuel would be necessary; none, in fact, except just enough to supply the leat lost by radiation. The reason is obvious. Let us suppose the steam has passed from the boiler, has entered the cylinder, has driven the piston forward, and is about to pass into the condenser, there to change its form, and be again converted into water. This steam, yet in the cylinder, and uncondensed, possesses all the heat it contained before passing out of the boiler. It has driven the piston forward, but in that effort it has lost no heat. That source of power it still contains,

Let it be supposed that the heat contained in the steam could, at the moment it is converted into water within the condenser, be saved, and by some device be again used to create steam from water within the boiler, with what exceeding cheapness could the power of the steam-engine be employed. But it is quite impossible thus to re-employ the heat of steam: it cannot thus be saved; and hence every effort to economize in this manner would be unavailing

The propositions we have here advanced were, it appears, more than twenty-five years since familiar to the scientific mind of Captain Ericsson. He was at that early period deeply impressed with their importance; and regarding heat as the sole source of motive power, was anxious to discover some element in which it could be so employed that, after giving motion to machinery, it should be returned to act over and over again for the same purpose. But little reflection was necessary to convince him that steam was not this element. It must consist of some permanent gas, and atmospheric air seemed admirably adapted to the purpose. Accordingly it was employed

In a work entitled " A Dictionary of the Arts of Life and Civilization," published in London in 1833, the author, Sir Richard Phillips, mentions an engine which Captain Ericsson then had in operation in that city, as “his application of excited or rarefied air to the performance of those powers of machinery, which hitherto have been made to depend on the intervention of boiling water and its steain." The author further states that he “has, with inexpressible delight, seen the first model machine, of five horse-power, at work. With a handful of fuel applied to the very sensible medium of atmospheric air, and a most ingenious disposition of its differential powers, he beheld a resulting action, in narrow compass, capable of extension to as great forces as ever can be wielded or used by man."

The author adds :—“The principle of this new engine consists in this :

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that the heat which is required to give motion to the engine at the commencemert, is returned by a peculiar process of transfer, and thereby made to act over and over again, instead of being, as in the steam-engine, thrown into a condenser, or into the atmospheric, as so much waste fuel."

During the last nineteen years, Captain Ericsson has employed much of his time, and expended large amounts of money, in overcoming those practical difficulties which are ever stumbling blocks in the way leading to the successful development of a great principle in new machinery. This he has now achieved. The principle of his invention, as stated by Sir Richard Phillips, is still retained, embodied in that practical and complete form, which render this engine economical, absolutely safe, durable, simple in construetion, and in action effective.

Let us now attempt to describe the regenerator, to which we have referred. Without this, the machine we examined would possess, in point of economy, no advantage over the best constructed steam-engine. With it, the advantages are incalculable. We have already fully illustrated the leading idea conceived by Captain Ericsson, of employing heat over and over again. To attain this is the object of the regenerator.

For the purpose of understanding this instrument our readers will bear in mind the construction and operation of the machine. We have before stated that atmospheric air is first drawn into the supply cylinder, from whence it is forced into a receiver, and that from this it proceeds towards the working cylinder, before reaching which it passes through the regenerator. This structure is composed of wire net, somewhat like that used in the manufacture of sieves, placed side by side, until the series attain a thickness, say of twelve inches. Through the almost innumerable cells, formed by the intersection of these wires, the air must pass, on its way to the working cylinder. In passing through these, it is so minutely subdivided that the particles composing it are brought into close contact with the metal which forms the wires. Now let us suppose, what actually takes place, that the side of the regenerator nearest the working cylinder is heated to a high temperature. Through this heated substance the air must pass before entering the cylinder, and in effecting this passage, it takes up, as is demonstrated by the thermometer, about 450° of the 480° of heat required, as we before stated, to double its volume. The additional 30° are communicated by the fire beneath the cylinder. The air has thus become expanded; it forces the piston upward; it has done its work-valves open-and the imprisoned air, heated to 480°, passes from the cylinder, and again enters the regenerator, through which it must pass before leaving the machine. We have said that the side of this instrument nearest the working cylinder is hot, and it should be here stated that the other side is kept cool, by the action upon it of the air entering in the opposite direction at each upstroke of the pistons. Consequently, as the air from the working cylinder passes out, the wires absorb its heat so effectually that, when it leaves the regenerator, it has been robbed of it all, except about 30°. In other words, as the air passes into the working cylinder it gradually receives from the regenerator about 450° of heat; and as it passes out, this is returned to the wires, and is thus used over and over, the only purpose of the fires beneath the cylinders being to supply the 30° of heat we have mentioned, and that which is lost by radiation and expansion. Extraordinary as this statement may seem, it is nevertheless incontrovertibly proved by the thermometer to be quite true.

When physical causes, productive of unexpected mechanical results, are carefully examined, they will always be found adequate to effect what, upon a cursory view might appear marvelous or incredible. Thus, after an examination of the reasons why this compact regenerator so effectually absorbs and transmits heat, its operation will cease to create wonder, although it cannot fail to excite profound admiration. We will state the causes of its efficiency.

The regenerator, contained in the sixty horse engine we have examined, measures twenty-six inches in hight and width internally. Each disc of wire composing it contains 676 superficial inches, and the net bas ten meshes to the inch. Each superficial inch, therefore, contains 100 meshes, which, multiplied by 676, give 67,600 meshes in each disc, and as 200 discs are employed, it follows that the regenerator contains 13,520,000 meshes, and consequently, as there are as many small spaces between the discs as there are meshes, we find that the air within is distributed in about 27,000,000 minute cells. Hence, it is evident, that nearly every particle of the whole volume of air, in passing through the regenerator, is brought into very close contact with a surface of metal, which heats and cools alternately. The extent of this surface, when accurately estimated, almost surpasses belief.

The wire contained in each disc is 1,140 feet long, and that contained in the regenerator is consequently 228,000 feet, or 41 miles in length, the superficial measurement of which is equal to the entire surface of four steam-boilers, each forty feet long, and four feet in diameter; and yet the regenerator, presenting this great amount of heating surface, is only about two feet cube-less than toto of the bulk of these four boilers.

Involved in this wonderful process, of the transfer and retransfer of heat is a discovery, which justly ranks as one of the most remarkable ever made in physical science. Its author, Captain Ericsson long since ascertained, and upon this is based the sublimest feature of his caloric-engine, that atmospheric air and other permanent gases, in passing through a distance of only six inches, in the fiftieth part of a second of time, are capable of acquiring, or parting with, upward of four hundred degrees of heat. He has been first to discover this marvelous property of caloric, without which, atmospheric air could not be effectively employed as a motive-power. The reason is obvious. Until expanded by heat, it can exert po force upon the piston. If much time were required to effect this, the movement of the piston would necessarily be so slow as to render the machine inefficient. Captain Ericsson has demonstrated, however, that heat may be communicated to, and expansion effected in, atmospheric air, with almost electric speed; and that it is, therefore, eminently adapted to give the greatest desirable rapidity of motion to all kinds of machinery.

We here close our imperfect description of a machine destined, as we believe, to work a revolution in the Commerce of the globe. It consumes but a very small proportion of the coal required for the steam-engine. It is entirely free from every element of explosion or of danger. Watchfulness is not imperatively required, as in the steam-engine. If left unattended, the worst that can happen is, that after exhausting the heat of its fires, and of its regenerator, it will stop. The one we examined, of sixty horse-power, has been run at full speed during twenty-four consecutive hours, consuming but nine hundred and sixty pounds of coal

. After feeding the fires, it continues to run three bours without replenishment, and after withdrawing them from the grates, it operates with full power for the period of one hour, in

consequence of the astonishing action of its regenerator alone. We believe we have not, in the slightest degree, overrated the immense advantages of this engine, in point of economy and safety. If we have not, the world may well start with exultation. In magnitude of results, no invention can rank with it. The electric telegraph is one of great interest and value, and to him who reflects that the fierce lightning has by that process been tamed, and brought to the very lips of man, there to be freighted with human language, and sent abroad, to girdle the earth with thought, it becomes sublime. Still, it is greatly inferior, in practical importance, to the discovery of a motive-power such as we have attempted to describe. Human speculation fails adequately to estimate its influence upon the social and commercial relations of men and of nations. Its effects will naturally be first exerted upon the ocean. It is here that the value of such a power will be most sensibly felt and appreciated. Here it will soon become the strong arm and right hand of Commerce. It may be affirmed with confidence that, with engines upon this plan, a ship of two thousand tons can be propelled from San Francisco to China and back with less coal than is now required for an ordinary ocean steamer to cross the Atlantic.

The annals of the mechanic arts furnish no instance of an important invention having been brought before the public in so complete a form as to warrant its being carried out on a scale of the first magnitude from the outset. Ericsson's Caloric Engine will form an exception. A ship is now building for its reception by Messrs. Perrine, Patterson, and Stack, measuring twenty-two hundred tons burden, and her engines, which are being constructed by Messrs. Hogg & Delamater, comprise four working cylinders, each of 168 inches in diameter. We have visited both the ship-yard and the engine manufactory, and have inspected with more than ordinary interest the work on which more than four hundred men are now busily engaged. The ship is quite a remarkable structure, both in point of form and strength. The engines being placed in the center of the vessel admit of a better form of midship section than in steamships. Of this the builders have availed themselves by giving such a rise to the floor that strength and easy lines for passing through the water are appropriately combined. The lines of the ship at the entrance are singularly fine; and yet, by a very judicious application of the “ wave line," as it is technically called, the bow possesses all the fullness requisite for a good sea-boat. The run is alike peculiar for easy lines, combined with stability and requisite bearing. The strength of floor, which is built entirely solid from stem to stern, surpasses anything we have seen in this country, noted as it is for producing the best ships in the world. In order to give additional strength to the ample timbers, the entire frame is banded by a double series of diagonal braces, of flat bars of iron, let into the timbers at intervals of about three feet, each series being riveted together at all the points of intersection. In addition to the ordinary central keelsons, there are six engine keelsons, bolted on the top of the floor timbers, for three-fourths of the length of the ship. On these keelsons the bed plates of the engines are secured by bolts passing through the floor timbers. These bed-plates extend over the entire area occupied by the engines, and present a continuation of iron flooring, not witnessed in any steamship. The security thus attained is further enhanced by dispensing entirely with the numerous holes through the bottom of the vessel

, which in steamers are necessary, and have often brought that class of vessels to a sinking condition. The engines being arranged in the center of the vessel, the decks are not cut off as in

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