CONDERT'S DIVING-DRESS. (From the Franklin Journal)

The diving-dress described in this communication, and the disaster connected with it, have been recalled to my recollection from noticing several recent patents for submarine apparatus. It appears to possess some peculiar features, and seems well calculated for small depth; no metallic or other inflexible material is used in its construction, or in connecting the two portions of it together. It is put on and off with the same facility as an ordinary dress; and when in use, the body is in full possession of its natural flexibility of

motion.

It was invented, and frequently used, by Mr. Charles Condert, a machinist, employed in a factory opposite the East river, in Brooklyn, opposite this city (New York). In the docks adjoining the workshop he repeatedly descended in it, in from 16 to 20 feet water. While thus engaged in August, 1832, he fell a victim to his enterprise. The air in the reservoir had become expanded, or, from some accident, probably from his falling, it had escaped, as the tube which conveyed the air from the reservoir to the interior of the dress was found broken when hauled up. He was, of course, instantly suffocated. Like Mr. Spalding, the improver of the divingbell, he perished in the bloom of life at a distance from his family, and in the. prosecution of his favourite pursuits. This description of his dress will probably be the only memorial of this ingenious, persevering, and unfortunate mechanic.

The dress consisted of two parts, made of cloth, coated with gum elastic; the under part was a pair of pantaloons, with India-rubber shoes; this portion of the dress extended up to the arms, and was supported by suspenders. The other part embraced the head, arms, hands, and the body as low as the hips, descending over the pantaloons about 12 inches. A piece of glass was fixed opposite the eyes, as at a.

His method of obtaining a supply of air was by condensing a sufficient quantity into a portable reservoir attached to his dress. It consisted of a copper pipe bb, 6 inches diameter, and 4 feet long, closed at both ends, and bent like a horse-shoe. Two or three staples were

soldered to the upper part, to receive hooks attached to the ends of the suspenders, or slings which supported it. Into this pipe he condensed, by a pump (formed of a gun-barrel), as much air as he supposed would be required for the time he intended to remain under water. A small valve-cock d, near one end of the reservoir, admitted air into the dress when required; by opening this valve a small pipe e from which entered two or three inches under the lower edge of the upper dress or jacket, where it folded over the under part. The air escaping from it, of course, entered the dress and kept it inflated, and prevented the water from entering it.

As the air was respired it ascended to the upper part of the hood or covering of the head, and escaped by a small aperfure in the cloth about the size of a pin's head, or less. He intended to use a valve in its place, but found it to act tolerably well. His situation below could always be perceived by the people above from the air ascending perpendicularly over

this orifice.

The round part of the reservoir embraced his back, and the two ends projected in front on each side of him.

When he descended, by a rope passed through a hole made in the bottom of the boat sufficiently large (about 2 feet square), a 56-pound weight was attached to one end and suffered to sink to the bottom; another cord attached to it, and one end held in his hand, or fastened to his arm, served to direct him to a perpendicular rope when he wished to ascend.

The reservoir was loaded with about 200 pounds of lead; this load was placed too high-it would have been better to have distributed it about the legs and feet; the higher the load, the more difficult it is for the diver to rise if he should happen to stumble or fall.

T. E.

Note by the Writer.-Might not the ordinary jackets of seamen be so constructed, that portions folding over each other might form receptacles for air, sufficient to prevent them from sinking, when from accident or otherwise they fall into the water, as is shown at A; or perpendicular cells might be quilted on them, as at B, without materially ehanging the present appearance of the dress. In almost every position in which a per

gon could fall into the water, some air would reinain in these cells.

DR. LARDNER'S EVIDENCE ON THE GREAT

WESTERN RAILWAY BILL

Sir,-The Mechanics' Magazine for the month of September having been just placed in my hands, I have for the first time seen what I suppose is a transcript of the printed Report of my evidence before the House of Lords. I perceive an error in the Report, which you would oblige me by correcting in your publication. In No. 632, p. 480, Mechanics" Magazine, I am made to say, that "if the train does not commence to move from the top of the inclined plane from a state of rest, we must add to the velocity ac-" quired in falling from a state of rest the initial velocity." What I stated was this; that we must add to the square of the velocity due to the descent down the plane from a state of rest, the square of the initial velocity, and that the sum thus found will be the square of the velocity of the body at the foot of the plane.

In the particular case mentioned, the velocity at the foot of the plane would be 50 miles an hour, and not 66 miles an hour. This error in the Report probably arose from the words of the question put to me being given as my answer.

As you have thought it worth while to reprint a portion of the report of my evidence, I think it right to state, that I had no opportunity of correcting that printed Report. I left London in two hours after I quitted the Committee-room of the Lords to attend the British Association in Dublin, and since then I have not been in London, nor have I even seen the Report of my evidence until I met it accidentally in your publication. It is probable, therefore, that there may be many other errors, especially in the numerical tabular parts. Every one who has been accustomed to scientific publications must be aware how difficult it is to insure correcness in this respect-even when the proof sheets have all the advantage of careful revision by the author.

I remain, Sir,

Your obedient servant,

DIONYSIUS LARDNER.

38, Cambridge-terrace, Edgeware-road, Oct. 22, 1835.

IVER MACIVER versus MR. HERAPATH'S FORMULA.

Sir,-Mr. Herapath ought to tremble -Iver Maciver I dare say thinks so-at the threat he has issued, that "Mr. Herapath's bed for some time to come will not be a bed of roses." Does Iver Mac, iver really think it is in the power of such a writer as he is, to make "Mr. Herapath's bed for some time to come not a bed of roses?" Before he undertakes this, I would advise him to go to the Temple of Truth, and study there a little; and afterwards to school for a few years, to acquire a little more of ele mentary mathematics.

Nothing, sir, is easier than for one man to deal out general invective against the writings of another: It is only when these carping pretenders come to deliver a little of their own, that the mist which conceals their want of knowledge is dissipated, and the profundity of their ignorance made manifest. Passing by Iver Maciver's assertions in his first and last paragraphs, which he knows, if he knows any thing, to be totally untrue, I shall stop at the first and only mathematical theorem he has ventured to give. He says, p. 43, "from a theorem derived from Nature's unerring laws, the velocity" of a locomotive train in miles per hour" will be

in which g32 and h is the perpendicular fall in feet of the plane.

Now, sir, being a plain man, fonder of deeds than words, I call upon Iver Maciver at once, mathematically, to demonstrate, with reference to locomotiveengines, and without shifting or evasion, this theorem derived," as he says, "from Nature's unerring laws." Let him not imagine that I do not understand what his theorem means; a schoolboy in Iver Maciver's own country would deserve to have his tartan petticoats lifted, and the birch briskly appli d, who could not see through it at a glance, as well as through its gross errors aud glaring absurdity. Remem ber, Mr. Editor, it is the mathematical proof of this theorem's containing the laws of locomotive-engines I want, and pray don't fail to unge him to let us

***

have it immediately without shifting and without evasion, allow me to repeat. Before I dazzle the world with a display of his refulgent knowledge, I am anxious to amuse your readers with an analysis of the logic of this heretofore breekless gentleman, who conceitedly threat

ens "for some time to come to make Mr. Herapath's bed not a bed of roses !" As soon as he has done this, I have a few other things for him to do, and we shall speedily see how much he knows of "Nature's unerring laws," and which he is most like-a man capable of opposing Mr. Herapath in science, or a swaggering, Bond-street butterfly, who insults the man that has deigned to notice him kindly, and gets contempt for his impertinence.

ANTI-CARPER.

THAMES TUNNEL.

Mr. Editor,-A correspondent of yours, G. L. S., in No. 632 of the Mechanics' Magazine a well-wisher evidently to the success of this great enterprise, condemning with justice the angry feelings expressed by some of your contributors against it, as attributable to personal motives, gladly and liberally offers a suggestion for the greater security of the work while in progress.

He says, that" to sustain the pressure of the superincumbent earth, during the excavation, he would drive 18 inches apart, horizontally, before the shield, and in a line with the top of the brick work, iron rods, 1 inch thick and 8 feet long, and that a sheet of iron one quarter of an inch thick should then be laid over every two of the rods; thus he would form over the shield a covering (or ceiling), which would be moved forward when a yard of tunnel is finished."

Prompted, as he is, by a friendly disposition, it is presumed that he will be gratified by learning what the provisions of the engineer actually are for sustaining the pressure of the superincumbent earth, while the excavation is being made. He should first know, however, wha' the scale of the operation is.

The excavation made for the Thames Tunnel is about 38 feet in width, and 22 feet 6 inches in height, presenting, therefore, an opening exceeding 850 feet. The whole of this excavation, including its two sides, which may be computed at

400 feet, is secured by means of a powerful apparatus designated the shield, as is also the roof of it, which measures 350 feet. At full tide the weight of both earth and water, which constitute the superincumbent pressure, is not less than 700 tons. This is the portion that has formed the subject of your correspondent's solicitude.

The ceiling of the shield consists of 24 or 26 pieces of cast-iron, denominated staves, closely adjusted; and as they are sometimes made to relieve each other, and therefore subjected to an increased load, they are for greater strength made like inverted troughs of cast-iron; their breadth is 18 inches, the depth of their sides 7 inches, and their length 9 feet, independently of a tail of wrought-iron which overlays the brickwork. The edges in front are made sharp for entering the ground, and the external surfaces of the staves are planed very true. Similar staves are laid against the sides of the shield, all planed and equally well adjusted; each stave can be impelled singly as sheet piles are. Upon the whole the shield may be viewed as a coffer-dam, which, instead of being moved in a perpendicular direction, is placed and is impelled horizontally. The standing part of the shield consists of 12 parallel frames, all independent of each other.

The front of this vast excavation is protected in a different manner from that of the sides. It is panelled all over with small boards, each of which is 3 feet long and 6 inches wide. There are, therefore, upwards of 500 of these boards, technically called polings, for covering the whole face of the excavation. Every one of these polings is held in place, and secured by means of two hand-jacks or screws, abutting against the frames. There are, therefore, upwards of one thousand of these jacks in action for securing the face of the excavation, or, rather, for pressing against the ground with sufficient power to prevent any disruption of its various strata; for were the ground to be at all deranged, the pressure against the sides and front of the shield might soon increase to 2,500 or 3,000 tons, independently of that of the superincumbent pressure.

It is further to be remarked, that every successive side, which at its full head is 76 feet above the foot of the excavation, causes an incessant variation in that pres

sure, tending to strain the hard strata, and to soften or knead the intervening soft ones; a fact quite unnoticed by projectors of plans, but which proved fatal to those who attempted the drift-way under the Thames in 1808. The pressure exerted against the front of the excavation by the agency of the shield, must therefore be uniformly kept at a maximum. The shield is advanced only 9 inches at a time, while the brick struc ture proceeds simultaneously.

Your correspondent, influenced as he is by the best motives, will have great satisfaction in learning, that the new shield is now being made without the necessity for modifying any law of hydraulics, or changing the nature of the ground, as has been too much the case with the various projectors who have sought to labour in the same field with the engineer of the Thames Tunnel.

Those who, without considering what must first be done under-ground, conceive that every difficulty would be obviated by some particular covering laid on the bed of the river over the tunnel, such as timber-flooring, rafts, planking, roofing, plates of metal of any kind, tarpaulings, sails, leather, &c., loaded over with some great weight, or not loaded at all, should further consider that they have, we are assured, upwards of 300 competitors for the same expedient, besides about 90 who, from motives of caution, have re served the disclosure of their respective plans, until some remuneration should previously be provided.

It would be well if those who feel disposed to enter the List of Competitors were first to consult the report of those miners who directed the attempts that were made and carried on with so much perseverance, between the years 1803 and 1808, with the ultimate object of opening a roadway under the Thames at Rotherhithe. These were miners (Cornishmen), engineers in that branch of the art, and, consequently, eminently qualified for the task in every respect; they were as sanguine, too, as any of the projectors of this day; and their excavation was limited, in the first place, to a simple driftway, the height of which was only 5 feet, the breadth 2 feet 6 inches at the top, and 3 feet at the bottom, forming, therefore, an excavation that was sixty times smaller than the excavation which has been made for the Thames Tunnel.

Diminutive, however, as this hole was when contrasted with that of the tunnel, the ground in the roof, though supported by substantial planking, gave way once in a fluid state, leaving an unsupported cavity over the roof of the driftway; still it held itself up; but a second accident of the same nature having occurred under a very high tide, the river broke the ground and entered the drift. In both cases it was the loose ground that forced its way first into the drift, and the river afterwards. The miners succeeded in filling the hole and in re-entering the drift, but the men could not continue the working; they were, according to the engineer's report, driven out of it by the frequent bursts of sand and of water, and it was acknowledged by him to be quite impracticable to proceed farther; so, after having probed the ground from underneath in many places, he concluded and reported that it was impossible to make an excavation of any size under the Thames. It never entered the head of this engineer, Mr. Trevethick, a remarkably ingenious and enterprising man, who conducted the operation to its final abandonment, that any covering, spread over the bottom of the river, would prevent the river filling his drift or a tunnel, at every tide, any more than it does the wells situated at many hundred yards from the river.

But he resorted to one expedient which he conceived would answer the emergency-one which, at any rate, demonstrates the intrepidity of this engineer. That is, in order to clear or pass through the place which had been filled up in closing the hole made by the breaking in of the river, he reduced the height of his drift from 5 feet to 3 feet. The men and the engineers, too, had therefore to work on their knees. Awful enough for such a task! Thus reduced, the area of the excavation of this drift hardly exceeded the one-hundredth part of that of the Thames Tunnel under corresponding circum

stances.

Any one can form an idea of a hole three feet square by looking at some garret-window; but not so easily of a hole of a greater sectional area-for example, than the old House of Commons was.

It is no absurdity, Mr. Editor, to have succeeded in cutting out a hole of larger area than that hall, under a head of water as high as the Custom-house, The en

gineer who has made it never, however, professed being a miner, and never excluded miners, or any person interested professionally, from a sight of his works.

Let us farther notice here what Mr. Vazie said, who was not only the colleague of Mr. Trevithick, but the directing engineer, so far at least as the first 392 feet of that drift. In his letter, by way of appeal, to the proprietors, dated the 7th of December, 1807, relying, as he somewhat emphatically assumed it, 66 on his professional information in the art of mining," he stated, "I am bold to say, that the only material difficulties with which we have had to contend have arisen from not having had the 50-horse steamengine," which had actually been purchased at his suggestion, and for which a 14-horse power had been substituted. He then adverts to "such an enterprise as that of working underneath a river so deep and so rapid as the Thames ;" and boasts of having, nevertheless,

suc

ceeded in defiance of difficulties_pronounced insurmountable by several engincers." In another part of his letter he adds, "I have been repeatedly, laboriously employed THROUGH THE NIGHT without taking any refreshment; and it was by no means unusual for me to remain 40 hours without rest; and for upwards of four years and a half I DID NOT SLEEP ONE NIGHT FROM THE WORKS-I am proud to state this, &c."

And all these arguments were from practical miners, who had but one miner and one carpenter to direct for making a shaft, begun on a diameter of 11 feet and completed at 8 feet; then carrying a driftway 5 feet in height, wherein not a single brick had been used.

Well may it be said, in respect to these great efforts towards making "convenient carriage-ways" quite water-proof,

"Parturiens mons, nascitur ridiculus mus!" And now not a vestige can be traced of these vast labours.

But of the Thames Tunnel there is to be seen that which demonstrates the practicability of the plan of Mr. Brunel, and knowing that it has withstood the shock of two irruptions of the river, we have a sufficient security of the strength of the structure to assure us, that when completed it will endure-a lasting monument to national enterprise and zeal in promoting practical science. We may at this period repeat what his Grace the

Duke of Wellington said of it in 1829, viz. "There is no work upon which the public interest of foreign nations has been more excited than it has been upon this tunnel;" and for a confirination of the interest felt in our own country we may refer your readers to the transactions in the House of Lords on the 2d of July, 1830, or of the House of Commons on the 24th of August last.

The reports of the former attenipts and proceedings were published in 1809 by the Directors of the Company, when they made a public appeal for plans, offering a liberal reward for that which should be adopted. Fifty-three plans were obtained upon this appeal. The practical and scientific men, to whom they were referred for examination, concurred in opinion that none would answer for effecting the object on a proper scale. All farther attempt was in consequence given up by the Company. A subsequent one, by working from above the river, proved equally unsuccessful.

Had your correspondent, Mr. Editor, in No. 605, been as solicitous for correctness as he is familiar with censure, he would not have felt himself called on to reprobate the Lords of the Treasury for having granted 250,000l. for the completion of an enterprise, so far completed as it is, which had received the fullest and most unequivocal approbation of his Grace the Duke of Wellington; no mean authority in such matters, more particularly when he had made himself familiar with those facts and circumstances already stated, but which is attempted to be denied by your correspondent. Nor is it other than natural that the late First Lord of the Treasury, Lord Althorp, should have been influenced in his decision by such sentiments as those publicly expressed by his Grace; as, for instance, "that the novelty of the work, the difficulty of ascertaining the nature of the bed of the river, and the accidents to which such a work was liable, tended to increase the expense of this great undertaking, yet that the work itself had cost only 120,000l." that is, at the period alluded to by his Grace, viz. the 11th of June, 1828, which included, however, the expense of the first eruption and part of that of the second. But up to the 31st of December, 1828, when the works were entirely suspended and were closed, the cost of the works of the tunnel, in