and whenever they exceed in any respect the limits assigned them, it is because those limits have been removed. But enough.

The Mohegan is one of the regular line of steamers which navigate the Sound between this city and Stonington. She is 150 feet long, 25 feet beam, 94 feet in the hold, and propelled by a low pressure engine, the cylinder of which is 42 inches diameter, and the range of the piston il feet. The motive fluid was furnished by two boilers,

11 alike in all respects, and similar in construction to those adopted in locomotive carriages. They are of copper, one-fourth of an inch thick nearly, or No. 4 wire gauge, and were new about four years ago, when the boat was built. They were placed fore and aft, on the guards.

The accompanying figures will convey a correct idea of the construction of the exploded boiler, and the location and extent of the rent. The cylindrical part, or shell, A, is 7 feet in diameter, and 10 feet long. The fire chamber B is 6 feet, making the entire boiler 164 feet in length. There are two separate fireplaces, a water-leg forming a partition between them. The interior tubes (also copper) are 3 inches diameter, and occupy about two-thirds of the shell. Thé ends of the cylindrical shell are connected to each other by bolts riveted to them, and also by rods passing through several of the tubes. The ends are also united by bars to the sides, but there are no transverse stay-bars.

The engineer appointed soon after the boat was built, remained in charge till a few weeks before the explosion. He generally used steam of 25 lbs. to the inch, and is said rarely to have exceeded 30 lbs. The latter was considered within the limits of safety, though certainly verging towards those of danger. It exceeds the amount that a copper boiler of such a diameter ought lo have been subjected to, according to the ordinary mode of calculation. From the comparatively large extent of fire surface, the evolution of steam was very rapid; and from the small space in the boilers for storing it, (small compared to the dimensions of the working cylinder,) particular care was required to prevent its undue accumulation. When the vessel was underweigh, the feed-pump was necessarily in almost constant requisition. It was not safe to allow it to remain many minutes unemployed. On account of excessive foaming, considerable experience with the boilers was necessary before a person could be certain of the height of the water within them. Oil was used to diminish the foaming. Wood was the fuel used.

The Mohegan left her berth in this city at 5, P. M., with 150 passengers. While passing through Hurlgate, the steam was turned off. from the engine iwice, in consequence of vessels crossing her path. The engineer states that he raised the safety valve on both occasions, and that it was while in the act of closing it, the explosion took place. Providentially, the rupture was in the starboard side of the starboard boiler, so that the contents, after blowing away the adjoining bulwarks, escaped overboard. Had the rent occurred on the opposite side of the boiler, the results must have been awfully appalling, as few of the passengers were below. Two or three persons were

A, cylindrical shell of boiler, showing the part ruptured, and a por

tion of the interior smoke pipes, or fues.
B, fire chamber. C, steam dome. D, chimney.
E, steam pipe. F, waste steam pipe and safety valve.
1, 2, 3, 4, elliptic hand-holes in the shell, at one of which (3) the

rupture commenced.
G, stationary weight on the lever of the valve.
H, movable weight.
X, Y, ruptured sheets.
z, transverse section of boiler at place of rupture.

slightly injured, but none seriously. Little injury was done to the boat, and none to the engine. The boiler was started by the recoil two feet, but was not overturned, nor the chimney pipe displaced. Both boilers have been removed, and will be replaced by a single one of iron, in which coal, instead of wood, will be used.

Several elliptic “hand-holes” were made in different parts of the boilers; there were four on each side of the cylindrical shell A, and arranged as seen in the figure. They are all of one size, viz., 63 by 4 inches. They were not originally formed in the boilers, but were made about two years ago, when the boat lay in Providence. Their edges are not strengthened in any way, but are plain and smooth, as the chisel that cut out the removed pieces, and the file, left them-an oversight, since the boilers were essentially weakened by them. Some precautions should have been taken to render the parts equally strong as before; a strong rim, or border, riveted round each hole, was necessary, as well to stiffen it, as to prevent the effects of checks, or notches, left by the chisel.

The utility of this will soon be apparent to the reader, if it be not already. The removal of the pieces cut from so large a copper shell, obviously rendered the borders of the openings incomparably weaker than any other part, and the interior covers made them still weaker, or, at least, had a tendency to do so. These covers lapped over them an inch, and were secured in the usual way; but it is obvious they transmitted to the borders of the openings the whole pressure to which they themselves were subjected. Thus, while the borders were less able to resist the force of steam than before the openings were made, a much greater one was accumulated through the covers upon them. Had the boilers been small cylinders of iron, the case would have been very different; but with comparatively soft and yielding copper, the action of the covers was not much unlike that of conical plugs, forced into openings to swell out their sides. Had the “hand-holes" been thus secured, the expense would have been trifling, and the boat might still have been running. With the exception of these "holes," with which the makers of the boilers had nothing to do, no defect whatever was to be found in their fabrication.

The rupture commenced near the bottom of A, at the hand-hole marked 3; this was in a line with 1. The rent was in the direction of the longer axis of the hole, separating the sheet, through its entire width, in nearly a straight line. The lower portion was blown outwards, and ripped from the adjoining sheets, on both sides, down to the deck; the upper one was torn, in like manner, from the neighboring seams, and thrown up to the roof of the boiler. See figures.

As the part of the boiler rent was cylindrical, of which no part was exposed to the fire, or to be otherwise deteriorated, it may be asked, What induced the rupture to commence where it did, in preference to any other place? Of course there was some cause for its beginning there? The circumstance alluded to at the close of the first paragraph, affords an answer to the question. A crack had long existed on each end of the hand-hole 3; one was an inch long, and the other rather more. These were noticed soon after the boat returned to the city, and were distinguished from the parts newly rent by having fragments of red lead on them, and which had doubtless been squeezed in from the gasket of the cover. I had an opportunity of examining them, and have now a small fragment of copper exhibiting one side of the shorter crack.

Both cracks were probably made by the workman who formed the opening. In driving out the displaced piece of metal, after making an indentation round it with the chisel, it had become torn in those places to the extent named; and, from the exceeding brittleness of the copper, this is not surprising. They had been closed carefully

, up, and were not afterwards very observable, if at all. These cracks, then, or rather rents, determined the place of the rupture, and gave the first direction to it. And it was fortunate that they did, considering the position of the opening (3) with regard to the boat and deck. The rents, or cracks, acted the part of a safety valve, and gave to the rushing fluid the safest of all directions. Other cracks are still to be seen on the borders of the hole, (see the ruptured sheets X Y,) but whether they were there previous to the explosion, is not known.

A deficiency of water has been suggested as an approximate cause of this explosion, but without any facts, I think, upon which to base it. It is said that, when the engine was at work, no deficiency could be detected on account of the foaming; but when the steam was shut off the last time at Hurlgate, the water would immediately sink to its level, and leave the dome of the fireplace bare; the dome would instantly be heated to redness, and, when the foaming again covered it with water, on the renewed action of the engine, such dense volumes of vapor were suddenly generated, that the boiler was unable to confine them.

One conclusive objection to this hypothesis is—had the fire dome even been heated to incandescence, as supposed, it must have been, beyond comparison, the weakest part of the boiler, and must, while so heated, have given way. Another is, the captain and engineers declare that the engine was never wholly stopped at the gate--its speed was only slackened, and hence the foaming could never have entirely ceased. A third is, there is no indication of any part of the boiler having been injured by the fire.

Generally speaking, there is but one opinion respecting the immediate cause of this explosion, viz., an excessive accumulation of steam. This was probably only temporary, and occasioned by the partial stoppage of the boat immediately previous. The engineer asserts that there was no more than 20 lbs. of steam at the moment of rupture, and he is considered both cautious and intelligent. Though recently appointed to the Mohegan, he has been in the company's service several years. He usually carried steam of from 22 to 24 lbs. When the boat returned to the city, two weights were observed on the lever of the safety valve, (see figure, one of which was reported to be an extra one; but this was not correct. Both weights had always been used--a stationary one, G, and the smaller one, H, used occasionally. Both were on the lever at the time of the explosion, the smaller one “about midway” between the end of the lever and the valve. In re

ply to the question, What steam was required to raise the safety valve when the lever was loaded with one, or both, weights? the answer was—with both, 23 to 24 lbs.; with the stationary weight only, from 17 to 18 lbs.

With the permission of Mr. H., the following data for determining the force required to raise the valve with one or both weights, were procured. The diameter of the underside of the safety valves is six inches, giving an area of 28.2 inches. The lever is a bar of iron, half an inch thick; at one end, three inches deep, at the other, one and a half. The distance between the centre of the fulcrum and that of the valve, 43 inches. The weight G was stationed 544 inches from the valve; it is a ball of iron, with an opening through its centre to slide over the lever, and a screw to fasten it in its place. Though not on the lever when examined, its place was strongly defined. It weighed 52 lbs. The weight H was suspended by a hook, or S, so as to be readily attached to any part of the lever; it weighed 28 lbs. The

pressure which the lever alone exerted on the valve, was 164 lbs. Then 52 x 114 (the distance between the valve and G, divided by that between the valve and fulcrum,) + 164–762 lbs., the aggregate load on the valve with the stationary weight only. This, divided by 28.2, gives rising 27 lbs. on the inch; but add iso lbs. for the weight H, and the force required to raise the valve could not have been less than 33 lbs., exclusive of friction, and that adhesion to which valves, it is well known, are subject.

The load on the valve, when not overcome by the steam, is, however, no criterion of the tension of the vapor at the instant of explosion. Of this, the gauge was the true and only test; and if the eye of the engineer was upon it immediately preceding the rupture, his statement that only 20 lbs. were on (if he was not mistaken) must be received. But the question then occurs how is it that the shell of the boiler should have given way at 20 lbs., when, under the same circumstances, it has withstood steam at quite, or nearly, 40 lbs.? To this it has been replied—“ The cracks where the rupture began had probably been strained, or started, and hence gave way with the lesser force.” This is very unsatisfactory, for, if they had been strained, they would have leaked; but admit they did not—if steam, of an expansive force equivalent to 35 or 40 lbs. the inch, ever started the cracks at all, they must have been instantaneously rent wide asunder, for they were weaker when started than the moment before; and even a less force could then continue the rent than the one which commenced it. It cannot, I think, be questioned, that part of the sheets which form

I the shell of the boiler, are of very inferior copper. The metal is so exceedingly brittle, that a single blow of a hammer has broken off portions as readily as if it had been bell-metal. Even pieces an inch square, on being laid over a hollow place, have snapped in two as if they had been spelter. Either the metal is deeply alloyed, or has been overheated in its manufacture, or else extremely hard rolled, though how the last operation could make its grain so short, is difficult to perceive. No responsibility could, however, in either case, be