the Philadelphia chimney of the chemists, which appears to be the model chimney of the State. It is argued that the plan of this chimney was brought from Europe as the best of all chimnies; that it has answered the purpose well; the nuisances of the former chemical works have disappeared from the air of Philadelphia, and the eminent firm of manufacturing chemists are sufficiently satisfied with the effect which has been produced.

But against this, it is to be remembered that the chimney is 126 feet in height; that the vast expense here incurred was for a purpose, to accomplish which capital was not regarde l so much as success, and that although air and smoke sufficient for a comparatively limited purpose can be passed through a tube of excessive length, this is no reason why the same currents of air should not be passed through better formed chimnies, of considerably less height, costing considerably less money, and looking very much more beautiful to the eye. The chimney of the Spring Garden chemists will "do very well," but that is no reason why other manufacturers ought not to go further into its merits before adopting, in other situations, a model which has no other merit than that it is the highest and most striking to the view of all the chimnies which yet have been erected in the United States.

It is also said that the same manufacturing firm have proved their case as in favor of the square chimney, by the erection of a circular chimney at their other works, at the Falls of Schuylkill, and that "no good has been obtained" by the erection of this latter chimney in a circular form. Here let it be observed that the chimney at the Falls of Schuylkill is circular undoubtedly, but it has been curtailed of its fair proportions, is deficient by full one-sixth part of the true columnar proportions, and it is not singular that no better effect should be produced in the draft of air through a stunted circle than through a square of redundant length. The chimney at the Falls of Schuylkill has no pretensions to the proportions of a model, and until a circular chimney, of the same height with a square chimney, shall be shown to have carried away a smaller volume of smoke, and therefore to have overthrown all the established principles of chemistry and mechanics, it is not sufficient that there can be a circular chimney, otherwise defective in its construction, which shall be no better than a square chimney, which has been built at double the expense.

The chimnies of steam engines scattered through Pennsylvania are almost all erroneous in formation, and particularly at the various iron furnaces of the State. There are chimnies built on the principle of the chimney of the chemical manufactory of Spring Garden, which, in consequence, waste an expense of thousands of dollars per annum for coal; one of these chimnies on the Schuylkill river, for a steam engine of 90 horse power, costing $7000 per year, at the rate of five tons of coal per day at $4 per ton; and yet the boilers of this engine are fitted with all the apparatus for conveying the hot air from the tunnel head of the furnace; nor would there be any coals whatever required were the chimney not built widening towards the top, and capable of carrying off only about one-third part of the proper column of air, which the furnace could easily supply.

The subject of the form of steam engine chimnies is one of leading importance to the iron manufacture of the State, and though iron furnaces are not situated in cities, and the ornamental is not the first of considerations,

yet is there very great loss of capital incurred by the erection of chimnies which, in the words of "H." are "square masses of brickwork of small elevation," &c.

To be a column, eight diameters of the base is the height of the shaft, and with a diminution of one-half of the diameter at the top, are, therefore, the leading proportions to be preserved in the view of the builder of a steam engine chimney; the external ornament of circle or octagon, of capital or none, and other such considerations, being of less importance, and depending upon circumstances for which there is no general rule."

For the Journal of the Franklin Institute.

The American Steam Navy.

In the October number of the Journal, I alluded to the steam vessels belonging to our Navy, and which at that time, including all classes, numbered seven. Since then, the "Edith" has been lost in the Pacific, so that we are now reduced to six, and five of that number are very indifferent vessels, leaving the "Mississippi" alone to sustain the credit of the country, and, so far as one vessel can, she will nobly do it.

There are now building four steamers, the "Powhattan," "Susquehanna," "Saranac," and "San Jacinto." The first at Norfolk, the second at Philadelphia, the third at Portsmouth, N. H., and the last at New York. The first two are 250 feet long, and 45 feet beam, and the last two are 196 feet long, and 37 feet beam. The first two have side wheels, and two inclined engines, each with cylinders 70 inches diameter, and 10 feet stroke; the third has side wheels and 2 inclined engines, with 60-inch cylinders, 9 feet stroke, and the fourth has a propeller and two inclined engines, working across the ship, with cylinders 60 inches in diameter, 4 feet 2 inches stroke.

When it is taken into consideration that, in war steamers, every foot of room possesses a double value from the large number of men that have to be accommodated, we may well inquire why it is that all of these vessels have engines that take up so much space in the ship, to the discomfort of every one on board. The space between bulkheads, on the "Susquehanna," is 89 feet of the widest part of the vessel. Without disturbing the arrangements of the boilers, engines of equal efficiency, and less weight and cost, could have been put in, and the whole space occupied reduced to 60 feet. In fact, no other form of marine engine at present known, could be spread over as much space as the inclined engine adopted in these vessels. To be sure, by adopting some other form, we could not have used several so called valuable American Patents, but what was lost by the inventors would have been doubly gained to the country.

The Board of Engineers, who determined the form of engines for these vessels, were of one opinion, that nothing but inclined engines should be used. Their reasons have never been made public, and while all the engineers of this country and Europe are in the dark as to the advantages of this form of engine, the Navy Department very unfairly keeps all the information to itself.

The use of the inclined engine has heretofore compelled the decking over of the lower part of the engine, to obtain room for stores, &c., and

in some cases, the firemen, who are roasted while on duty, have been almost boiled when in their rooms. The "Missouri" was burnt by having a store room over the engine.

The forms of engine most used in the English Navy at present, are ver tical direct action and the oscillating, and they have been well proved as worthy of confidence. But the fact of their being well tested there appears to have been an objection to their use here. We must have American engines; our flags are entirely different, why should not our engines be so? And we have the satisfaction of knowing that our engines are independent and original.

In examining a list of the builders of machinery for the English Navy, the names of Maudsly, Napier, Seaward, Fawcett, Boulton & Watt, Rennie, Fairbairn, Penn, and other celebrated builders, appear, all of whom design the engines they build, the plans being first approved by the Government, and a superintending engineer being stationed at the works. By this means, the talents of all the builders in the country are made available, and the competition between them stimulates all to active exertion, and the cost of Government engines does not exceed that for private service; while here, the system that prevails is opposed to improvement, and while it enhances the cost of the engines at least one-third, is productive of no good to any one, not even to the contractors, who would much prefer a different system.

It is to be hoped that the present Secretary of the Navy, who is not committed to the errors of the past, will take a proper view of the matter, and if so, any steamers that may be built during his term will be done in one-half the time, and at two-thirds or three-fourths the present cost, while their machinery will take less room, and give more comfort to all on board. X.

For the Journal of the Franklin Institute.

Description of a Hygrometer, for Regulating the Moisture of the Air in Closed Apartments. By JOHN M. BATCHELDER.

In a letter of Franklin, addressed to Edward Nairne, of London, a plan for a hygrometer is mentioned, which was afterwards made by Mr. Nairne, and is described in Vol. IV., page 449, of Sparks' edition of Franklin's

Works.

In this instrument the motive power is derived from a slip of wood, one end of which is fixed, and the other end attached to the short arm of a bent lever, which is moved by the expansion and contraction of the wood, the extent of the motion being shown upon a graduated arc at the extremity

of the lever.

Having found that an hygrometer resembling this, which I have used for several years past, is very readily affected by changes of moisture, I have made one upon a similar plan, and attached to it an apparatus which will produce any required degree of moisture in the apartment in which it is placed. An instrument of this kind will not indicate the dew-point with accuracy, neither can two instruments be made to give precisely the same expansion or contraction when exposed to the action of the same degree

of moisture; it is, therefore, of no value for observations that are to be recorded and compared with each other, but each instrument, when used in conservatories, or in any place where the temperature is nearly uniform, will, if the air becomes too dry, restore it to that degree of moisture that has been previously determined upon as the most desirable.

In the annexed figure, A, B, and C, represent standards of wood which support the apparatus; E is a lever having its fulcrum at F. Upon the top of the perpendicular rod H, which rests upon the horizontal lever, a light open mouthed vial or cup, I, is placed, having an orifice and lip, S, at its side, near the top; this contains about one gill of water, its weight and the weight of the long arm of the lever being balanced by the counterpoise G. Jis a slip of bass wood, (Tilia Americana,) four feet in length, two

inches in breadth, and one-eighth of an inch thick, the grain running in the direction of its breadth, or horizontally. This wood should be perfectly sound, of straight grain, but not of very close texture, its exterior being made rough by the use of coarse glass paper, in order to expose a larger surface to the air. At the bottom of the standard B, is a nut and adjusting screw, W, to which the slip of bass wood is attached; a plate of brass is screwed to the top of the wood, and is fastened by a pin to the lever E; from this lever a silk thread is carried around the pulley L, in a spiral groove; the axis of this pulley passes through a dial plate and carries an index. At N is a vessel of water, having a proper supply pipe leading to it, the water being retained at a uniform level by the waste-pipe P, and connected with the water in the small vessel by a syphon. The respective length of the legs of the syphon is immaterial, as the flow of the water depends upon the relative level of the surface of the water in the reservoir, VOL. XVIII.-THIRD SERIES.-No. 6.-DECEMBER, 1849.

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and that in the cup; both legs being immersed, the syphon remains constantly filled with water.

To put the instrument in operation, let the apartment be kept at its mean temperature, and at the degree of moisture required, both of the vessels and the syphon being filled with water. After the instrument has been exposed to this atmosphere a short time, turn the screw at W until the orifice in the vessel I is level with the top of the waste-pipe P; then turn the pulley L, and set the index at zero. The instrument being thus adjusted, if the air becomes more dry the slip of wood contracts, the small cup descends, and water flows into it from the stationary reservoir; the water then escapes from the orifice in the side of the cup, falls into a funnel, and thence into a pipe, which, when the instrument is used in green-houses, conveys the water to evaporating pans placed upon the flues, or to a horizontal pipe, having openings at its upper surface at suitable intervals, from which the water falls at any point desired. As the water thus discharged evaporates, the surrounding air is moistened, the wood is expanded, and when it attains its original length, the orifice in the cup is again raised to the level of the surface of the water in the reservoir, and the flow of the water ceases. If, from any cause, the air should become too moist, the only effect produced is, that the cup continues to rise, and a small quantity of water flows back to the large reservoir.

If, by accident, the air should become very dry, the further contraction of the wood causes a larger quantity of water to issue from the cup than is due to this change in the hygrometric state of the air, the discharge being accelerated as the difference of level between the two surfaces increases; thus the return of the air towards its normal condition is the most rapid at the time when it is of the most importance that the moisture should be restored. The same degree of moisture may be made to discharge a greater or less quantity of water, by moving the fulcrum of the horizontal lever to the right or to the left.

The opening and closing of valves and stop-cocks is attended with much friction, but in this instrument, it will be observed that the water flows through the syphon with a very small amount of friction, and that little power is required to depress the cup. This plan may, therefore, be used to advantage in many instruments in which the motive power is small, the weight of the water discharged being applied to produce more extended or more forcible movements.

Boston, November, 1849.

For the Journal of the Franklin Institute.

Particulars of the Steamship "Ohio."

This fine mail steamer, recently finished for the line between New York and New Orleans, via Charleston and Havana, has just left on her third trip, and the following particulars concerning her may be of interest to the readers of the Journal:

Length of keel, 240 feet; length on spar deck, 265 feet; depth of hold from spar deck, 33 feet; do. do. from main deck, 25 feet; breadth of beam, 46 feet; by government measurement, 2300 tons. She is fitted with two