above the steam drum-it also had the usual glass water gauge, blowcocks, &c. On one side was a small engine to work extra pumps, and on the other side of the main boiler, was another engine to drive the blower, these were supplied with steam from a small high pressure boiler. The top of the boiler and its steam pipe was covered with hair felting to prevent the radiation of heat. By the testimony of the captain and others of the boat, given on oath at the inquest held on the body of Mr. Stillman, of the Novelty Works, New York, it was stated that the safety valve was adjusted to blow off at twenty-five inches of the mercury gauge before mentioned, and at twenty-six inches the steam would blow off freely, which was the case before the steamer left the wharf on this excursion trip. All that had noticed the water gauge and gauge cocks a short time prior to the explosion, concur in the opinion that there was plenty of water in the boiler; this I believe from the many indications on the wreck. The pressure of steam, as was shown by the gauge tube, and seen by many different observers a short time before the boiler gave way, range from twenty-two to twenty-six inches-weighing all the opinions on this point, I do not think that it exceeded the mean (24) inches). Now from the opinions of those on board, that the boiler did not make steam freely or enough, (and this is quite plausible,) the short time elapsing, from ten to fifteen minutes, at which the pressure was noticed, would not admit of a great increase of steam from the ordinary action of the fire, and the question arises, how did the explosion take place? As no part of the boiler remains, with the slight exception of some rivet heads, and a broken stay which had been inside the boiler, the answer can only be conjectural.

The power consisted of a horizontal condensing engine, with balance valves, and Sickel's cut-off; it is similar in plan, but far superior in workmanship, to one built at New York city and in use here. The cylinder is forward of the wheel shafts, and the boiler ahead of the cylinder, the furnace end being near the bow.

At the time of the explosion, the ash pan was moved a little ahead, and turned up on its edge; it is in good order; all of the grate bars and some of their bearers were thrown above fifteen feet from their original position on to the forecastle, they are uninjured; the same is the state of the foremast; it was wetted with dirty water, on each side, about twenty feet high; a little ahead of the boiler front remain, on each side, two posts or stancheons (unhurt), which support the carlins of the boilerdeck, some of the end pieces of boards still remain attached to them; these shew the marks of the dirty water; all the deck covering the boiler aft to the front of the small cabin, has been carried away. Bricks, and many pieces of light sheet iron work, and the broken steer-wheel are strewed on the main deck, some of the cast iron stands and pieces of sheet iron are carried aft nearly to the wheel shafts, and one check valve complete was thrown into the engineers' work-room, where also the second engineer was blown, and escaped with a slight scalding. The engine is scarely injured; the separation of the steam pipe from the side pipe, has been by the tearing and breaking of all the flanch bolts, leaving the vulcanised rubber joint remaining in good order; the end of the throttle

valve lever being fastened by the usual thumb screw, remains as it was at the time of the explosion; the steam passed this valve through a double crescent formed opening, measuring one-half inch at the greatest space; the diameter of the valve chamber being 15 inches, gives such an area for the steam way as, for the size of the cylinder, 56 inches by 10 feet stroke, and a cut-off of about stroke, and a working pressure of 24 lbs. to the inch, would confirm that "the boat was going along regularly."

All of the copper pipes, such as the feed, and blow pipes, &c., attached to the lower part of the boiler, pass up through holes in the main deck, and are torn off nearly where they were connected with the boiler; they consist of heavy copper, and the soft solder on the ends of some of them give no indications of over heating; these pipes being on both sides of the boiler, near the ends, remain battered, and each set drawn out on the deck, slightly inclined aft towards the starboard and larboard sides, in lines nearly at right angles with the centre of the hull. The top of the starboard wheel-house is shattered by some solid body coming in contact with it. On the arch of this wheel-house, outside of it, and the after part of the boiler deck, and the top of the cabin, (the most abaft) there are many pieces of sheathing paper, felting, and small pieces, &c., dust of anthracite coal, (I send you a piece of the largest, which is partly consumed, and a piece of the hair felting, the fibres being perfect, with the dirt attached,-it and the piece of coal were near each other); along with this coal dust there still remained much water where it could be retained, both on the top of the cabin as well as the boiler and main deck, and the dampness and dirt showed the inside edge well defined, as a small part of the deck was perfectly dry and clean.

The report was different in sound according to the position of those who heard it, thus: those nearest and above, described it as "dull;" further aft, "as a double report," (probably the boiler first, and the crashing of the wood work); and those at a distance off, "as a dull booming sound like a distant cannon;" whilst those on the main deck heard no report at all. One of the deck hands, sitting abaft the wheel shaft, in the passage formed by the wheel-house and engine timbers, heard nothing, but was knocked over by a rush of cold air, (something similar to the windage of a cannon ball). It is confirmed by different persons, that there was a discharge of water and steam from the safety valve pipe an instant before the explosion.

My opinion of the explosion is this: that one or both of the middle arches gave way, and the lower part of the boiler opened out sideways, driving every thing outside before it, and tearing off and stretching out the pipes on deck, as before mentioned, and discharging part of the water in its flight, and then the upper part (or probably all) rose up in the air slightly inclined to the starboard side, tearing off the steam pipe at its joint with the engine; and as the boat moved ahead, a part of it came in contact with the top of the wheel house, and here as the mass had nearly come to a state of rest, the remaining water, coal dust, &c., was discharged from it on the upper deck; the mass of iron then fell into

the river off the starboard quarter. One or more arches may have given way from the breaking or tearing away of the stays, for it amounts to nothing that the pressure was less at that time than it had been before, for all conversant with machinery know that parts frequently give way when doing the least work. Another hypothesis is, that the intense local heat from anthracite coal just at that time may have caused the water to be driven out of the middle legs of the arches, and by opening the fire doors, pumping in water, or some other cause, the water passing back into the heated legs assumed the spheroidal state, or was otherwise instantly flashed into steam. That there was a sudden increase of pressure seems supported by the water and steam coming out of the safety valve pipe, by the valve being jerked up, and the water from the condensed steam formed in the pipe above the valve being ejected from it; or the safety valve may have been raised by the engineer, and if the first supposition is correct, the commotion caused by it produced a shock and started the rivets and stays of the arches.

That there was no neglect in the management of the boiler, seems certain, for there were too many practical men about not to notice it if such was the case; all who knew the first engineer, Mr. Samuel Hill, speak in the highest terms of his professional ability, and give him the rare quality of being over cautious; he received the cause of his death at his post along side of the engine, which he only left from time to time. to pass quickly to and from the fire-room. The engine was made at the Messrs. Leeds' foundry. No one can say how many lives were lost, as many had gone aboard without an invitation; five have died since the explosion. It is intended to recover the boiler if possible;-if it is found I will furnish you a drawing of it and any other particulars I may learn. I have been rather prolix in this account, but I preferred to give all the light on the subject I possessed, as it is only by apparent trifles that we will arrive at the solution of preventing steam boiler explosions. I may not be out of place in making a suggestion, which I have thought of doing for a long time. I have heard much testimony given on oath respecting explosions, without at all bringing out facts in a scientific point of view which would be invaluable data. I would recommend that a code of questions, covering every supposed circumstance attending a boiler before and after its explosion, be drawn up by the General Government, printed, and furnished to the authorities of each city, or to gentlemen of known scientific and mechanical knowledge, with power to take testimony on oath, and that the questions and their answers be transmitted to one of the bureaus at Washington City; by this means much valuable information would be elicited for the benefit of all.

P. S. The steamer "Knoxville's" boilers exploded at the levee a few hours ago, 6 P. M. You shall have the details in a few days.

A. C. J.

The rivet heads, found on the deck, are square breaks, such as rivets present by the very common habit of hammering too long; one end of the stay rod is torn off, and in the flattened part of the other end remains part of a broken rivet.

For the Journal of the Franklin Institute.

What constitutes an Engineer?

Within the last twelve months there have been three explosions on the Delaware, one at Baltimore, one at or near New Brunswick, N. J., and one at New York, all of them being boats belonging to this city, or but very recently from it. In two cases the safety valve was tied down. In three the boilers were too weak 1or the pressure used, and in one a probable want of water was the cause. In the first the guilty reaped their reward by immediate death. In the second the engineers in charge were made to suffer from the ignorance or carelessness of others. The introduction of high pressure steam tugs on our waters has materially enhanced the dangers arising from the use of steam, particularly as these vessels, from the simplicity of their engines, are often entrusted to men who have no idea of the responsibility of their position, and are entirely ignorant of the first principles of steam. Much ignorance prevails in the community on this subject. If a man has a greasy jacket, and rails at anything like theoretical knowledge, he is immediately set down as a sound practical man. Now there are many grades of engineers, each competent in his grade, but out of it often at a loss. There are those who may be called constructing engineers, whose business it is to design and superintend the construction of engines; of this grade there are several varieties. One may be perfectly at home on marine engines and know but little of locomotives, and the reverse; but each will understand the general principles of the other, although deficient as to details. Then there are two classes of practical engineers; one of which is a mechanic and is engaged in building, while the other is employed in running the engine when finished. The first of these may be ignorant of the details of practical operation, and the last is too often ignorant of the first principles of mechanics, either practical or theoretical. This last class do the mischief. They are those who literally kill their thousands, not intentionally, but through ignorance. The history of steam navigation on the Western rivers is a history of wholesale murder and unintentional suicide. We say the general diffusion of knowledge prevents crime-a truth none deny and we raise money for free schools that all may have the privilege of enjoying them, and at the same time employ engineers who know nothing of the principles of steam or practical mechanics. If they are prudent, things go on pretty well, but if rash, we soon have the records of a fatal accident; if the engineer is killed, that ends the matter; if not, he is ready to swear, if necessary, that the boiler had a plenty of water and very little steam, rather below the average, and a report is made out which states that no one is to blame. At the West they rather enjoy these things than otherwise, and one year as a fireman has in times past been a sufficient recommendation as an engineer. I must not be understood as saying that all of this class are such as I have just been describing, but that it is too often the case. I am acquainted with some who, by years of practice, have become well worthy of confidence; but these men are now the last to deny, and the first to appreciate the value of proper theoretical or mechanical knowledge. Taking things as they are, and knowing the

fact that, for a few dollars a month, some owners of steamers will employ the ignorant, should not some means be taken to protect the community from the cupidity and ignorance to which they are too often subjected? We have laws that compel all owners of steamers to have their boilers inspected every six months, while at the same time we allow them to have any person for an engineer. A proper inspection of those who have charge of steamers is necessary to the public good. FULTON.

On the Form of Shafts and Axles. By MR. THOMAS THORNEYCROFT.*

In order to arrive at proper proportions for any of those principal media of power, which are so fully employed in almost every branch of manufacturing science peculiar to this kingdom, two or three leading points obtain, as axioms on which to reason, in order to arrive at satisfactory results.

Taking, for instance, iron as the material in question, it is required to apply it in an entire new sphere of mechanical movement; the first leading point for examination is the law which limits the tensile and compressive powers of that material, and should the various forces which are about to be put into operation, be by any means calculable quantities, the tensile and compressive powers of the material being determined, there is before us an easy mode of arriving at satisfactory results.

It has, however, been found of equal importance thoroughly to investigate the cause of every failure in this material, and mark those parts where the greatest amount of weakness appeared, so that in re-construction the simple laws of strength, as determined by experiments, are applied in connexion with the results of practice, in producing principles of form and mechanical arrangement, better and safer than either of them alone would have done: yet, notwithstanding that by these means safer results have been obtained and brought into use, from the rapid advance of mechanical contrivance, the moving parts of machinery are being daily subjected to untried and incalculable forces; hence the necessity of uniting to former experiments and practice, experiments and contrivances as closely analagous to the peculiar circumstances which are found to operate so powerfully in deteriorating and destroying that most valuable material now under consideration.

It would be deeply interesting to trace the many changes which have taken place in the formation of the various structures, both of cast and wrought iron, which have been brought into use during the last fifty years; some of these remain to the present, monuments of the skill of their projectors, and at the same time proofs of the soundness of the principles on which they have been constructed: on others, causes have been in constant operation, gradually reducing the strength of the original mass until they have become unfitted for the purposes of their erection.

In not a few instances these causes of weakness have been detected, and proper remedies applied by better arrangement of materials; and, in some instances, by the adoption of entire new principles of construction.

From the London Artizan, for November, 1850.