piston and rod within it was leaning against the end of one of the boilers. The cast-iron end of the starboard boiler (marked F in figs. 1 and 2,) was blown into the Captain's office near the stern of the boat, a distance of forty-six feet from its original position on the deck; and although two inches thick, was broken in two, both pieces were drawn out from among the bedding while I was present. But it was towards the bows of the vessel, where the most violent effects had taken place, and where nothing was left to indicate the force which had thus cleared all before it. It was here the chimney was located, (C in fig. 1,) but not a particle was left, the whole was blown into the air and then it fell into the river.

Nothing remained of the short cross boiler, (marked T in fig. 1) to which the ends of the two long ones were united, with the exception of such portions as are shown at fig. 3, and these were straightened out as represented.

The destruction of some, and the displacement of nearly all the machinery, rendered it difficult for a person not previously acquainted with the boat to detect (from the wreck before him) the mode by which the boilers were connected, or the arrangement for feeding them. It was not till the day after the explosion that I became aware of these and some other particulars. It is unnecessary to say any thing here respecting the engine, as its peculiarities are noticed in the testimony before the coroner. I may merely observe that the large cylinder was twenty-four and a half inches in diameter, and that both pistons had metallic packing.

The Henry Eckford had two wrought iron cylindrical boilers—see fig. 1, which represents their upper surfaces as seen from above, and as they appeared before the explosion. They were ranged fore and aft upon the middle of the deck-were nineteen feet long, thirty inches in diameter, and were placed eighteen inches apart. The furnace and fire door were towards the stern of the vessel, and the chimney C, was near the bows. The ends of the boilers over the fire were of cast iron, and connected at their lower parts by the feed pipe D D. Ris the steam pipe with a branch and flanch at right angles, to which the one that led to the engine was connected. C C, the gauge cocks. The opposite ends of the boilers were united to a short one T. The larboard boiler L, being connected by a species of elbow joint, while the junction with the other was at the side, as represented. The open part of the short one being closed by a cast-iron end E. Besides being thus connected at their extremities, a passage from the interior of one boiler to that of the other, was formed below the water line, by a short pipe P, nine inches in diameter; and to the middle of this was joined another, O 0, which was continued through the furnace and fuel beyond the fire door, where the feed pump was connected to it. This long tube was named the heater; its object being to heat the supply water before the latter entered the boilers. The front part of O O, passed through the furnace below the pipe D D, to which it was connected by a short vertical one, which I have endeavoured to represent at fig. 2.

There were two valves on the larboard boiler, A B fig. 1. The latter was one inch and three-quarters in diameter. The lever, weight, plug and rod were blown off and lost; nothing but the seat of the valve being left. The other one, A, was two and one-quarter inches in diameter, the distance between the centre of the fulcrum and that of the valve three and a half inches, and the lever four feet long; the weight is lost. As the upper edge of the lever had no notches or other graduated marks, and as the head of the valve rod had only a plain socket through which the lever was loosely slipped, it would

VOL. II, 3RD SERIES.-No. 1.-JULY, 1841.

2

seem that the pressure of the steam could not have been very accurately ascertained, but must have been in a great degree guessed at. The small valve was close to the end of the boiler; it was formerly weighted to blow off at 150 lbs. on the inch, but at the time of the explosion, according to the engineer's account, at fifty pounds. It was named the tell-tale, and when steam escaped from it the other one was opened to let off the excess. It will be perceived that both the safety valves and gauge cocks were attached to the same boiler; no opening being in the starboard boiler S, except for the steam and feed pipes.

The present condition of the boilers may easily be stated. The part T, as already observed, was blown off, leaving the ends of Land S entirely open, with fragments hanging round them. These fragments show that the most part of T was greatly worn, and the texture of the metal deteriorated. Along the edge at Y (fig. 3) is was reduced from one-fourth of an inch, its original thickness, to onetwentieth of an inch, and even less in some places. The specimen No. 1 is from this part. No. 2, a piece that is only two and threequarter inches in length, and not one and a half in width, exhibits the same or nearly the same extremes of thickness, and was taken from near the place marked X, while the largest specimen is from Z. The lines of separation are, in all instances, through the sheets, and not in the lines of the rivets; this circumstance may be accounted for from the fact that the heads of the rivets protected the metal over which they extended from corrosion, as seen in specimen No. 2, while the rest is, in most cases, worn to extreme thinness.

The end F of the starboard boiler carried with it a complete ring of the metal to which it was riveted, the line of separation being at N, fig. 2. At this place the metal is about its original thickness and appears to be little worse than new. To account for this part giving way, while so much stronger than others, the rupture may be supposed to have been effected on the same principle as that by which the barrel, or breech, of a musket is burst when heavily charged with powder, and the wadding not rammed home. On this supposition a rapid and excessive accumulation of steam must have taken place, and the circumstance of the end F having exploded favours such a conclusion, for had the vapour been gradually evolved, the numerous weak parts of both boilers, one would suppose, would have first given way, or at any rate that the part T would alone have been blown off. The uncertainty respecting the quantity of water in the boilers might also be adduced; for as the engineer tried the gauge cocks the moment after blowing off steam, we know that the foaming of the water consequent on the latter operation would render all immediate appeals to the gauge cocks useless-at such a time water would have been given

out had the cocks been placed on the top of the boiler. But it is not necessary to seek for the cause of this explosion any further than in the state of the boilers; they are completely worn out. Had the end F not been blown out, and thereby counteracted to some extent the effect of the rupture at T, both boilers would probably have been hurled to some distance from the boat. It is singular that no person was scalded with the hot water; neither the engineer, who was standing at the gauge cocks, and was knocked to one side of the boat, nor the fireman, who was partly in front of F, fig. 1, and carried, he knew not how, to the stern of the boat, received any injury. Nor was there any signs of water in the direction which the moving masses took. The end F was shot into the Captain's office, driving the front before it, but no water had followed, since every thing appeared dry when I saw it taken out.

The pipe P of very strong wrought iron, was entirely laid open, and O O, separated from it. The steam and feed pipes, R and D D, were broken and carried away. At H, fig. 1, there was a long rupture in the middle of a sheet, but it had obviously been caused by the sharp edge of some heavy machinery falling on the place. At the edge of the first sheet on the end of the boiler L, fig. 2, and on a level with the water line, is a small triangular hole through the metal, which I have tried to represent at J. Each side of this hole does not exceed three-quarters of an inch, and so far from its having been produced by a blow, it bears every sign of the piece displaced having, been corroded away. The edges present no signs of fracture, and they are as thin almost as the thinnest specimens sent. Other very thin places have been detected by hammering in the same region. THOMAS EWBANK.

New York, May 5, 1841.

Civil Engineering.

Extracts from the Treatise on Geodesy, by L. B. FRANCŒUR. Translated by W. H. EMORY, Lieut. U. S. Topographical Engineers.

[CONTINUED FROM PAGE 374, VOL. I.]

[Translated for the Journal of the Franklin Institute.]

19. The Compass.-This instrument is formed of a box, in the centre of which, supported on a point, is a steel needle, n s, (fig. 28. pl. II) rendered magnetic. It is a well known property of the magnetic needle that it takes a direction called the magnetic meridian, which is constant nearly for the same locality, and which does not vary much from that of a line running north and south.

The magnetic needle is a blade of steel, A B, (fig. 27,) long, slender, and pointed at the two ends. It receives the magnetic property by rubbing it with a magnet from one end to the other and always in the same direction. A cap of brass, or what is better, a cap of agate, is fitted in the needle, near its centre of gravity, which is scooped out in the shape of a cone, the apex of which rests on a very fine point, upon which the needle traverses with scarcely any friction, and is left free to present its two ends to opposite points in space.

If the needle before being magnetized is horizontal, or balanced when placed on the point, it afterwards takes a direction very much inclined to the horizon, and is brought back to a horizontal position by placing a piece of wax on the end which is uppermost.* Thus the process of magnetizing causes the needle when freely suspended to take a fixed direction, oblique to the horizon, and in the plane of the magnetic meridian. The inclination being overcome by applying a weight, the needle is left free in the horizontal motion, and takes a direction which at Paris is north-westerly and differs from the true meridian 22°. This direction changes with time and place, but for our purposes it is sufficient that it remains the same for many days together, in each locality. The northern and southern ends of the needle are called respectively the north and south poles. They are marked N and S, or sometimes to distinguish the northern end of the needle it is rendered blue by heat.

The power which determines the horizontal and vertical motion of the needle, seems to be the force of attraction exercised by large masses of iron in the interior of the terrestial globe, which by the known power of the loadstone to attract iron, forces the needle to take positions in the direction in which this power is exerted.

20. The compass represented in fig. 28, is a smooth square box containing a circle plated with silver, which is divided into three hundred and sixty degrees, and into half degrees. In the centre, and perpendicular to the plate, is a pivot of tempered steel, upon the point of which a magnetized needle, n s, turns freely upon its cap, so that the two ends of the needle pass very near the graduated circle without touching it, and enable the observer to read the graduation to which the needle corresponds.

The box is of wood, or of copper; iron is carefully excluded from it; and even the observer must not carry a key or any other article of this metal about him, by which the needle will be made to deviate from the magnetic meridian. The box is fastened together by dovetailing, or by brass screws. A glass fitted over the circle and held

Copper wire is generally used in the United States as the counter weight for needles of the surveyor's compass.