know exactly how much there is in steam, high or low. If Watt had used the former, and passed the steam from his cylinders into atmospheric ones he would have left little for his successors to do.

Of fourteen marine engines built by one firm in this city, the average cylinder is 45 inches diameter, with 8 feet stroke; the air-pump 30 inches and 3 feet stroke. All, except three, are calculated to work with steam up to 30 lbs. on the inch; hence every cylinderful at that tension contains three of common or uncompressed steam, and, when condensed as one, two-thirds of the power which might be drawn from it are lost. The cylinder holds 93 cubic feet, the condensation of which ought to contribute an amount of force equal to 93 tons raised one foot. We know it does not and cannot yield half of it; yet that amount ought to be doubled if the vacuum were produced in separate cylinders.

When the subject is duly considered, the inducements to adapt condensers to atmospheric cylinders, can hardly be resisted, as generally double the power will be obtained with no extra working expense but that of ice or water for condensation, and not even that for adding to the power of marine engines, as they have it without pumps to raise it. As the power increases with the pressure of the steam, such engines instead of 30 lbs. on the inch may be safely reduced in their dimensions and worked at double or treble that amount. None can more readily and beneficially realize the change. Their steam cylinders may be converted into atmospheric ones, and replaced with others one-third or onefourth their size. Economy as respects space is not more obvious than in fuel and power. To increase the power of a steamer's engine at present, she must take in a larger cargo of coal; on the plan here presented she need not take in an additional bushel.

Invaluable beyond expression as steam power is, and is to be, it is strange that atmospheric pressure has not been more cultivated. It is uniform, while that of steam is variable and always less in the cylinder than in the boiler. The full effect of the vacuum is obtained on the easiest terms, whereas from the direct pressure of the steam there is a heavy discount. Make all engines on the proposed plan, and the steam power of the world may be doubled, if not more than doubled wherever water is cheaper than coal; and, as with marine engines, requires neither cartage nor stowage.

To engineers it would be superfluous to add anything more; but there are those who do not perceive how fresh force is to be got out of waste steam without fresh fuel, nor how it is to be used. They want something more to make the matter clear to them, and for that purpose the annexed figure is introduced. They understand how one force is the production of heat, and it will explain how the other is evolved by cold, or the abstraction of heat. The steam cylinder is left out, as its action requires no explanation. Its waste pipe is all that is wanted to supply the steam that is to be converted into power. A portion of it is represented.

A and B are sections of two atmospheric cylinders open at top, each being two or three times the capacity of the steam cylinder, according to the pressure of the steam used. c, the waste steampipe; D, the condenser; E, the cold water pipe; F discharges the heated water. The positions of the pistons indicate that the steam piston has just descended in its cylinder and discharged its contents into B. On being condensed, the piston of B is pressed down by the atmosphere and that of A at the same time raised to receive the steam from the upward stroke of the steam piston, which, on being in its turn condensed, excites the pressure of the atmosphere to press down the piston of A and raise that of B. The fly-wheel, as usual, carries the crank over the dead points. The valves to admit the steam alternately into A and B, and those that turn on and off the condensing water, are too well known to require being figured.

Of course it makes no difference whether the steam cylinder be horizontal or vertical, fixed or oscillating.

As the atmospheric pressure on the pistons of A and B is limited. to their downward stroke, their rods are here represented as connected to the vibrating beam by chains. But as the force of the steam on first entering will suffice to raise them through a considerable part of the stroke, which is so much power gained, the connexion should be made in the usual manner.

In this way the two forces may operate two distinct engines, one

animated by fire, and power in the other evolved by water. Taken together they constitute the most effective device for eliciting and economizing the motive fluid, and this they do by the natural process of giving each its full play, unembarassed by the other.

There are other points which need not be dwelt on here. They may be placed in separate rooms or buildings, and if in such cases the steam and atmospheric piston cannot be relied on to move simultaneously, the steam may be discharged into a receiver, from which the atmospheric cylinders might draw it.

Waste steam from other sources may thus be converted into power. If the proposed system did not harmonize with the exhaustion of both forces it could not be the true one, but the fact is patent that it does, for the more dilated the vapor before condensation the more facile its conversion into water. It has never been decided where the line of pressure should be drawn between condensing and noncondensing engines in order to give the best effect to the former. European engineers place it quite low, while here it has been run up to what has been thought too high. Now, the truth is there is no such line, for the results of condensation keep pace with the direct force, whether that be of five or fifty atmospheres-another proof that the system is what it is claimed to be. It completely reverses the hypothesis, "the greater the pressure under which steam is raised the less is to be gained by its condensation." That may possibly apply to superheated steam. It is perfectly true of our condensing engines, from which it was deduced.

Fig. 2-a mere variation of the preceding one-will serve to show how the proposed plan comprises the exhaustion of the expanding as well as the contracting force. This has hitherto been deemed unattainable, and, but for the system of condensation in separate cylinders, it would still be an impossible problem.

The cylinders, A, B, are horizontal, and both pistons attached to one rod, which passes through a stuffing-box connected to the closed ends of the cylinders. c supplies the waste steam; D, a valve or three-way

cock, communicating with c and A, B; E, a similar one, with passage from the cylinders to the condenser, F. Suppose the steam cylinder (not represented) working with steam of 60 lbs on the inch, its piston half the diameter of A and B, and with the same length of stroke. The arrows indicate the passage open between A and the condenser, and steam passing into B, against whose piston it acts in unison with the atmospheric pressure moving forward the piston of A. Thus the steam in B keeps expanding with the receding piston till its force expires at the end of the stroke. The valves are then reversed, and the same thing takes place in A.

Let experience determine the difference between engines on this plan and those of Hornblower and Woolf.

fig. 3.

Fig. 3, outline of an engine in which the steam and atmospheric cylinders are combined. To engineers details are unnecessary. The steam cylinder is placed between and on a line with the atmospheric ones, and connected directly with them. The three pistons are on the same rod —the steam and exhaust valves, and stuffing-boxes-as in Fig. 2. By such an arrangement side-pipes are got rid of, and also the additional waste of steam for "clearance," there being no chance for water remaining in the cylinders to arrest the pistons.

There are those who question the rationale of the popular cut-offs. If no more steam enter a cylinder than sufficient to overcome the resistance, it matters little whether it enters at once or flows in to the end of the stroke. In the latter case, the motion is equable, and the engine not strained by varying the momentum. Hence, the alleged gain, it is said, can only be the per centage of power unnecessarily employed at the first part of the stroke. Leaving the question for others to settle, it is enough to observe that by using steam as here proposed, expansion may be carried to an extent that will, in a great measure, if not wholly, supersede the use of cut-offs. No power can be lost by their non-usage.

VOL. L.-THIRD SERIES.-No. 1.-JULY, 1865.

Condensation. The preceding page was designed to close this paper, and condensation to form the subject of a separate one, but as that might engross too much space, an illustration with brief remarks is given here.

It may be, as some think, that the contemplated saving of power cannot be realized in steamships with the current system of condensation and low steam. According to some engineers, the working of what is called the airpump alone consumes 10 per cent. of the whole power of the engine; others vary it from 15 to 20 per cent., and others again make it much more. Mr. Prosser, C. E., in the Journal of the Franklin Institute, for May, 1856, observes: "The low pressure air-pump condensing engine is thought by some not much of a tax on the power of the steam, but good authority shows that it is an enormous one. Dr. Ernst Alban says, 'out of 17 lbs. total pressure, only about 7 lbs. are made available for useful effect." It is strange that an experimentum crucis has not put an end to such diversity of opinions on a matter so important. If any such have been made I know not where to look

for them. I cannot, however, resist the conviction that a thorough investigation will lead, sooner or later, to the abandonment of "low" steam.

It is proposed to maintain the vacuum by the same power that acts upon it-by connecting the condenser with a pipe having a perpendi