Fig. 9, is a section of the float, being a double cone, that is, two cones united at their bases, made of thin sheet copper. The lower one being the float proper, the upper one terminating in the tube B, which has a female screw formed at its end: o o are two short bent tubes, to preserve a communication between the steam in the boiler and the interior of the float; they are preferred to mere holes, as they prevent mud, &c. from falling into the float when thrown up by the agitation of the fluid.

U, is a tube six inches long and two in diameter, securely fixed on the top of the boiler, four inches of its length being inside, and the rest outside of the boiler; a screw is formed on the latter part. The neck of the float or tube B is made to move easily in U, which thus serves as a guide. Y, is a tube rather longer than the depth of the float; a screw four or five inches long is formed on it at X, which fits into the corresponding screw on the neck of the float: a sufficient length is given to X, to adjust by it the float to the required surface of the water in the boiler. S, is a nut to screw on X, close to the top of the float, after it has been united to the latter, to steady them; a collar may be placed between them, to make them steam tight, though this last is not necessary. The lower end of Y reaches to within half an inch of the lowest part of the float. Its upper end is formed into a valve, which is ground air tight to its seat at V; it is made a little spherical to admit of the small motion or play of the neck of the float in U: in the centre of the valve seat, or the part ground, are drilled two small holes, half an inch in diameter, through which the steam escapes, when the valve opens, by the sinking of the water, thus giving notice of the fact.

W, is made to screw on U as represented, it serves as a guide to the part of Y above X: its upper part is formed to receive the under side of the valve, which may be ground to fit it, (the die is not essential,) so that when the valve is opened, all the steam which escapes may pass through the float. It is also conveniently separated from U for the purpose of altering or adjusting the depth of the float in the boiler by means of the screw X. The committee will perceive that the pressure of the steam against the valve, is neutralized by its pressing equally (through the tube in the float,) against the valve seat at V. The whole of the parts are represented together in fig. 10; the water in the boiler being as high as required, the valve is closed. Suppose the water to subside half an inch, the valve opens and the steam escapes through the float, up the tube Y, and through the small openings at V. I placed over V, a trumpet mouthed organ pipe, the noise of which was so great as to draw the attention of people in the street, (190 feet distance,) who supposed the boiler had burst. I afterwards closed one of the openings as the other was quite sufficient for every purpose of a tell-tale, by the noise of the escaping steam, without the addition of any instrument whatever.

It may be supposed by some persons that water (condensed steam,) would collect in the float and so destroy its buoyancy, but I never found this to be the case, although I have frequently unscrewed W, and taken out the tube Y: indeed, were it to collect there, it would

open the valve by its weight, and be expelled by the steam. This, however, never took place but twice, both of which times the feeding pump had been suffered to work until the water had risen nearly to the small tubes o o, when of course it entered the float, but gave immediate notice of the excess of water, by being expelled through the openings at V.

The agitation of the water, has little or no effect on this float; this, however, may be owing to the small size of the boiler and engine. The valve is never opened until the water is on the verge of its prescribed limits, when the valve will alternately open and close, perhaps twice, in the space of a minute, thus giving notice of the approach of a decrease of water. In such cases, a few, say six to eight, strokes of the pump will silence it. After the valve is completely opened, fifty strokes of the pump invariably close the valve. The boiler, as before mentioned, is twenty feet long, and two feet in diameter. The diameter of the feeding pump is two and three-eighths inches, and the length of its stroke six and a half inches. These dimensions, taken in connexion with the facts stated above, show the very small decrease in the depth of the water in the boiler which is made known by this float. The committee will perceive that the float cannot sink more than one half an inch whatever may be the decrease of water in the boiler, as its lower part rests, when opened, that distance upon the corresponding part of W. That distance for the valve to open is abundantly sufficient. The valve itself is only five-eighths of an inch in diameter.

I have made many other floats during the last three years, but this embraces the best features of them all; it is therefore unnecessary to describe them at present.

The last cause of explosions mentioned in the commencement of this paper is neglect. Perhaps every thing that could be said on this subject, has been anticipated in those communications already published by the committee, I therefore pass to the consideration of the means proposed for confining the effects of an explosion to the vicinity of the boiler itself.

For this purpose bulk heads have been strongly recommended. Perhaps they could not be made to impart equal security, to take up less room, &c. better than in the form of an extra boiler, or strong cylindrical casing of iron, inclosing the boiler proper, with a certain space between them. When boilers are placed fore and aft, and on the guards, the end of this casing might be left open. This plan would have important advantages which no bulk heads could possess. The space between it and the boiler, would allow for the expansion of the steam in case of explosion, and by its cylindrical form, the effect would, in a manner, be isolated, and so prevented from expending its energy against the boat. I have no doubt, however, that a steam-boat may be made quite secure without either of these devices. The different subjects proposed to be embraced in this letter, have now been discussed. I shall be much gratified should my communication contain any thing calculated to prevent explosions, or to increase our confidence in the use of the steam engine, that "noblest work of man." THOMAS EWBANK.

Continuation of the Report of the Committee of the Franklin Institute of Pennsylvania, appointed May, 1829, to ascertain, by experiment, the value of Water as a Moving Power.

(Continued from p. 377, vol. ix.)

WHEEL NO. III.

The diameter of this wheel was ten feet. The wheel having been substituted for No. II. and the necessary alterations made in the apparatus, the friction of the wheel and drum was examined, and ascertained to be, in each, one per cent. of the weight applied.

The differences of weight which were applicable to the experiments with the larger wheels, would have been too considerable for that under consideration. Variations were made occasionally of fourteen pounds, and usually of twenty-eight, or fifty-six pounds; the leads of 103 lbs. were sometimes used to make up a considerable weight. With small apertures it was found necessary to remove the leads which in the former experiments were contained in the iron basket. The friction table will, therefore, contain instead of the usual constant resisting weight the weight when the leads were removed, and the additional friction for fifty-six pounds, from which that for the different weights is easily obtained.

The weight raised by this wheel was never sufficient to suspend the shaft.

Constant inactive weight.

Weight of the wheel,

Weight of that part of the chain which was

between the barrel of the shaft and the drum, Weight of the drum,

Total,

Friction upon this at one per cent.

Constant resisting weight.

That part of the chain which was between

the barrel of the shaft and the ground,

Weight of the iron basket,

Total,

Friction upon this at one per cent.

Friction from constant weight,

The centre of gravity of the water upon this wheel, (see Fig. 3, Plate V.) was 3.02 feet from the axis, and the barrel about which the chain was wound was one foot from the same axis; hence to raise 146 lbs. and overcome a friction of 22.10 lbs., the constant friction just found, required a weight of water of

Friction due to this at one per cent.

Total amount of friction when the weight raised was 146 lbs.

55.66 lbs.

.56 lb.

22.66 lbs.