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that no other cause for explosion would have been looked for, than the action of this steam. The case is, however, otherwise, and the Committee must turn aside from their direct course to examine briefly the theory which assigns the production, and subsequent destruction, of hydrogen gas, as the cause of the explosion. According to this view, the water thrown upon the metal is decomposed, and hydrogen gas evolved; or a similar decomposition of the steam, by the hot metal, takes place. This hydrogen, becoming mixed with oxygen, is ignited by the red-hot metal, and an explosion ensues. The difficulty of furnishing oxygen for the hydrogen to combine with. has lately been met more satisfactorily by Mr. Perkins, than it had been by any preceding theorists. He asserts that air is frequently drawn in by the operation of the forcing pump, and is thus accumulated in the boiler. The primary hypothesis, in regard to the production of hydrogen, having been fully disproved by the experiments of this Committee, there is no necessity for examining the minor ones; it may be well, however, to observe, that if air were introduced into a highly heated boiler, containing hydrogen in too large a quantity either to combine explosively, or silently, with the oxygen of the air, that element would be taken up by the heated metal; and that gases cannot enter, and remain without mixing with the steam, and being carried out with it. In the experiments of the Committee, which have been referred to, water was thrown upon the bottom of a boiler, heated to orange redness, without being decomposed. In fact the scale of oxide existing upon the bottom, prevented the decomposition of water, by enfeebling the affinity which would produce it. This boiler was carefully cleaned, and in good working condition; a condition in. which no one need be told, a boiler has not a bright metallic surface.

23. Carburetted hydrogen does no doubt exist at times in a boiler, in greater or less quantities, from the decomposition of oil, or of vegetable substances introduced to stop leaks, or to prevent deposits, but nothing warrants the idea that it can accumulate and mix with air, so as to be dangerous.

In furnaces where coal is used as a fuel, it will be seen in the sequel that gas, if prevented from escaping by the closing of a damper, may collect, and may possibly be a

The reader should refer to these, that he may see the care which was taken in them. A negative result requires so much more caution than a positive one, that more time was devoted to those cx. periments in order to make them satisfactory, than the Committee deemed warranted by the importance of the subject. Report of Com. on Explosions, Part I. p. 61, &c. Jour. Frank. Inst. vol. xvii. P. 217.

source of danger.+ The ignition of a mixture of coal-gas and air in a furnace has been known to destroy it, as also of a mixture of gas from resinous wood and air; but these are cases altogether foreign from the subject under discussion.§

24. The explosion of the steam-boat Enterprise, on the Savannah river, is said to have occurred at the instant the boat was struck by lightning. This has been advanced as confirming the hydrogen hypothesis; but no inference can fairly be drawn from an accident, in regard to which the circumstances are so little known. If there was hydrogen present, there must have been unduly heated metal, and the direct action of electricity on the non-conductors around the boiler, may have so displaced it as to bring water upon the heated metal, and thus to effeet an explosion. This, like the other supposition, is mere hypothesis. It is certainly, however, quite as contrary to analogy, that an electric spark should pass through any part of a space, like the interior of a boiler surrounded by a conductor, and thus explode a mixture of hydrogen and oxygen within it, as that it should shatter this extensive conductor by its direct action. The Committee consider the circumstances of this case as too ill-defined to draw any inference from it, certainly not one which is contrary to sound theory, by which they mean general induction from numerous well-observed facts.

25. Another case has been urged with much more appearance of directness in the testimony. A boiler in the Union rollingmills, at Pittsburgh, burst with a tremendous explosion; a cylinder with one of the heads attached was thrown out of the works, and rising to a considerable height in the air, fell nearly 200 yards from its former bed. A passenger in a boat which was near at the time, describes a stream of fire, as issuing from behind the boiler, which, according to the hypothesis under discussion, was a stream of burning hydrogen. It is almost needless to remark, that if hydrogen had been the

+ Explosion in the Gold mines as given by John Taylor. Esq. Philos. Mag. vol. i.

M. Arago states this to be the fact, on the authority of M. Gay Lussac. A furnace was thus destroyed at the Paris arsenal. Annuaire du Bu reau des Long. 1830, p. 197, and Jour. Frank. Inst. vol. vi. p. 54.

See the case of an explosion of a sheet-iron drum attached to an anthracite-stove, with its explanation by Prof. Hare. Jour. Frank. Inst. vol. vi. p. 337. Pine shavings were used to kindle the fire, the gas from which, mixing with the air in the pipes and drum, produced au explosion, when the flame from the kind ed shavings rose into it. Refer also to the explosion of the bellows of a smith's forge. Silliman's Jour. vol. xxiv. p. 192.

-cause of the explosion, it would not have burned in a stream behind the empty boiler as it rose; the observation is, however, perfectly well explained by Dr. Jones,* by the stream of light which appears to attend every luminous substance moving rapidly, on account of the duration of the impression upon the eye. That the boiler was red-hot, there appears no doubt.

26. From this digression the Committee return to the pursuit of their subject. They conceive that it has been fully established, that the presence of unduly heated metal is dangerous, both from the weakness of the material, and the possibility of its producing highly elastic steam. They, therefore, proceed to examine the probable causes leading to this result, and which have been suggested either in the communications made to them or in other documents, and the proposed remedies for, or precautions against, the danger.

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Sir,-Having occasion to fit a footwheel to a mandril with three groves, I find considerable difficulty in ascertaining what the relative circumferences of the three groves on the foot-wheel must be, to enable the same band to fit the corre sponding circles on both. Not being much of a mathematician, I have, after a few unsuccessful attempts to find a rule applicable to the case, given up the calculation in despair, and unless some one of your talented correspondents will assist me, I shall be obliged to have recourse to diagrams, and constructing circle after circle on the foot-wheel, by actual measurement ascertain when they approach the proper size. I have no doubt that by this means a result may be found near enough for most practical purposes; but it will be a most tedious and unsatisfactory way of arriving at it, and when found will be only applicable to this one particular case. I have stated my difficulty to several practical men, and they have acknowledged they are unacquainted with any rule which can assist me, and that they have themselves been similarly inconvenienced from the want of one. If, therefore, any of your readers can favour me with a solution of the following question, and any rule which is applicable to such cases generally, you will enlighten several of your readers and very much oblige,

I am, Sir,

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circles on the mandril, so as to enable the same band to fit them equally well; the centre of the mandril being fixed 30 inches above the centre of the foot-wheel?

DURABILITY OF WOOD.

(From the Genesee Farmer.)

The subject of the durability of different kinds of wood when exposed to the action of air and moisture, though one of great importance to the farmer, and the public at lage, does not seem to have received that degree of attention and elucidation it deserves. The Teak tree (Tectona Grandis) of the East Indies, and the Live Oak (Quercus virens) of our southern forests, appear to be nearly indestructable when employed as timber, and in naval architecture. But these from their natures cannot be cultivated in the northern States, and we must seek in our forests trees which shall approach or rival the above in excellence and durability. Fortunately these qualities are found nearly in perfection in the Yellow Locust (Robinia pseudacacia), and the Red Cedar (Juniperus virgininaa), and in a lesser degree in many others; a knowledge of the compa rative durability of which, properly ascertained, would be of essential service to the public.

Thirty-two years since, in enclosing some newly cleared field, we had occasion to set some bar posts, and, at a point where four fields cornered, we placed one so that it served for four pair of bars, one to each field. The post was the common white cedar (Cupressus thuyoides), cut from a thrifty tree fourteen inches in diameter, the holes on the four sides cut in the usual manner with a narrow axe, the bark stripped from the whole, and the large end set two feet in the earth, which at that place was rather moist. After standing more than twenty years, or until the basswood fences with which it was connected had rotted down, it was removed to another position, where it has since served for two pair of bars and one gate. At the time of removal it appeared quite sound, and present appearances indicate a duration of another twenty years at least. From our experiments we are convinced that large posts are far more durable than small ones, and that those which occupy the whole diameter of the tree, are better than sawed or quartered trees of equal size.

In the Railroad Journal, in an article on the advantages of lime, as a preservation of timber, the following instance of its effect on the durability of the white pine (Pinus abies), is given :-The planks were a parcel

of pine planks used as platform on the ground, on which to make live mortar.This platform was laid by the informant's grandfather in a corner of the yard, and used every year more or less for the purpose of a mortar bed. His father continued it in the same use; himself, the grandson, continued it for a time, as long as he had occasion, after which it lay some years unused, and overgrown with grass and weeds. At length, wanting the ground for another purpose, he had it torn up and removed, expecting to find the planks entirely rotted, but, to his surprise, found them sound, and, to use his own forcible expression, "as hard as a bull's born." This was after they had lain exposed to all the vicissitudes of the atmosphere, and in contact with the surface of the earth about sixty years.

In the year 1800, a Mr. Atkinson, in the employ of the Hudson's Bay Fur Company, discovered, on Old Factory Island, in James' Bay, a branch of the Hudson's Bay, a cedar post, about a foot square and five feet high, on which the following inscription had been cut, and all the letters of which were distinctly visible:-"In the year 1692 wintered three ships at this Island, with one hundred and twenty-seven men, under the government of Captain James Knight. Then we erected this monument in remembrance of it."

This furnishes the greatest instance of duration of timber set in the earth, and con. stantly exposed to atmospheric influences, we have any where noticed, and we believe there are few kinds of timber which would endure so long. This notice does not state the kind of cedar employed, but, from its frequency on those islands and coasts, there can be no doubt of its being the red cedar, a kind which, as stated above, is almost imperishable.

Next to the kinds above stated, rank in durability the various kinds of pine and spruce; the white oak, chestnut, red elm, black walnut, and red beech; all furnishing timber of good quality, but not such as will, like the above, resist for a long period the attacks of time, In purchasing timber, price should not be so much regarded as quality and durability, as a rail or a post that will last fifty or sixty years, is worth far more than the usual difference charged between such, and those which will endure only twenty-five or thirty.

FORCE OF THE WATERS.

(From Audubon's Ornithological Biography, Vol. ii.)

It was the month of September. At the upper extremity of Dennisville, which is itself

a pretty village, are the saw-mills and ponds of the hospitable Judge Lincoln, and other persons. The creek that conveys the logs to these ponds, and which bears the name of the village, is interrupted in its course by many rapids and narrow embanked gorges. One of the latter is situated about half a mile above the mill-dams, and is so rocky and rugged in its bottom and sides as to preclude the possibility of the trees passing along it at low water, while, as I conceived, it would have given no slight labour to an army of woodsmen or millers to move the thousands of large logs that had accumulated in it. They lay piled in confused heaps to a great height along an extent of several hundred yards; and were in some places so close as to have formed a kind of dam. Above the gorge there is a large natural reservoir, in which the head waters of the creek settle; while only a small portion of them ripples through the gorge below, during the latter weeks of summer and in early autumn, when the streams are at their lowest. At the neck of this basin, the lumberers raised a temporary barrier with the refuse of their sawn logs. The boards were planted nearly upright, and supported at their tops by a strong tree extended from side to side of the creek, which might there be about forty feet in breadth. It was prevented from giving way under the pressure of the rising waters by having strong abutments of woodland against its centre, while the ends of these abutments were secured by wedges, which could be knocked off when necessary. The temporary dam was now finished. Little or no water escaped through the barrier, and that in the creek above it rose in the course of three weeks to its top, which was about ten feet high, forming a sheet that extended upwards fully a mile from the dam. My family was invited early one morning to go and witness the extraordinary effect which would be produced by the breaking down of the barrier, and we all accompanied the lumberers to the place. Two of the men on reaching it threw off their jackets, tied handkerchiefs round their heads, and fastened to their bodies a long rope, the end of which was held by three or four others, who stood ready to drag their companions ashore, in case of danger or accident. The two operators, each bearing an axe, walked along the abutments, and at a given signal knocked out the wedges. A second blow from each sent off the abutments themselves; and the men leaping with extreme dexterity from one cross log to another, sprung to the shore with almost the quickness of thought. Scarcely had they effected their escape from the frightful peril that threatened them, when the mass of water burst forth with a horrible uproar.

All eyes were bent towards the huge heap

of logs in the gorge below. The tumultuous burst of the waters instantly swept away every object that opposed their progress, and rushed in foaming waves among the timber that every where blocked up the passage. Presently a slow, heavy motion was perceived in the mass of logs; one might have imagined that some mighty monster lay convulsively writhing beneath them, struggling with a fearful energy to extricate himself from the crushing weight. As the waters rose the movement increased; the mass of timber extended in all directions, appearing to become more and more entangled each moment; the logs bounced against each other; thrusting aside, demersing, or raising into the air those with which they came in contact: it seemed as if they were waging a war of destruction, such as ancient authors describe the efforts of the Titans, the flamings of whose wrath might to the eye of the painter have been represented to the angry curlings of the waters, while the tremulous and rapid motions of the logs, which at times reared themselves almost perpendicularly, might by the poet be taken for the shakings of the confounded and discomfited giants. Now the rushing elements filled up the gorge to its brim. The logs, once under weigh, rolled, reared, tossed and tumbled amid the foam as they were carried along. Many of the smaller trees broke across, from others great splinters were sent up, and all were in some degree seamed and scarred. Then in tumultuous majesty swept along the mingled wreck, the current being now increased to such a pitch that the logs, as they were dashed against the rocky shores, resounded like the report of distant artillery, or the angry rumblings of the thunder. Onward it rolls, the emblems of wreck and ruin, destruction and chaotic strife. It seemed to me as if I witnessed the route of a vast army, surprised, overwhelmed, and overthrown. The roar of the cannon, the groans of the dying, and the shouts of the avengers were thundering through my brain; and, amid the frightful confusion of the scene, there came over my spirit a melanhcoly feeling, which had not entirely vanquished at the end of many days. In a few hours almost all the timber that had lain heaped in the rocky gorge was floating in the great pond of the millers; and as we walked homewards we talked of the force of the waters.

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by R. W. Fox, Esq., which was described and figured in the last report of the society.

Two premiums, the first of seven guineas, the second of three guineas, by G.S. Borlase, Esq., for the best and second-best chemical or mechanical plans for ventilating mines, which can be applied to the Cornish mines with advantage.

A premium of ten guineas, by G. C. Fox, Esq., for the best essay on the various diseases incidental to miners, their causes, and the best practical means of remedying them. Any statistical information as to their longevity, compared with that of the other population of the county, will be deemed highly desirable.

A premium of ten pounds, by John Herle Tremayne, Esq., for the best available method or improvement on the plans already suggested, for facilitating the ascent and descent of miners, provided the judges shall consider it to possess sufficient merit to be entitled to the premium.

A premium of three guineas, by John Taylor, Esq., for the most complete and accurate accounts of the quantity of water supplied to the boilers, the number of bushels of coal consumed, and the duty performed by an engine, for a period of not less than six months in the ensuing year.

A premium of ten pounds, by the Rev. Canon Rogers, for the most economical, safe, and efficient plan for lighting mines, consistent with the health of the miner:-such plan to be accompanied by a statement of the present actual consumption of candles, and the cost per dozen lbs., at some of the principal Cornish mines.

Two premiums, the first of ten pounds, the second of five pounds, by H. H. Price, Esq., of London, civil engineer, one of the honorary members of this society, for the best and second best practical plans for adapting to steam vessels the method used in Cornwall, of working steam expansively; including practical drawings of the construction of the boilers and expansion-gear. Such boilers should combine economy of fuel with safety, both as regards the danger from explosion, and accidents to the vessel from fire: with suggestions as to the best method of preventing the loss of heat, by radiation or otherwise. Due regard must be had to the essential difference between a single acting engine working pumps by a lever, and two double acting engines working cranks.

Three premiums, by Charles Fox, Esq., the first of three guineas, for the best model (either original or copy) not less than eighteen inches in length, of a life boat, which shall be judged most manageable in a storm; the second premium of two guineas, for the second best; the third of one guinea,

for the third best. Economy in the construc tion is a great desideratum.

Three premiums by Charles Fox, Esq., the first of three guineas, for the best description and drawings of the least inconvenient and inexpensive, and, at the same time, most efficient means of securing a fortnight's supply of bread and water, within reach of a ship's crew, in the event of their not being able to go below deck, owing to the vessel being water-logged, or to other causes; the number of the crew may be estimated in the proportion of 15 tons register to each man. The second premium of two guineas, for the second best; the third of one guinea, for the third best.

All plans should be accompanied with ac⚫urate models or drawings, estimates of expense, and all the information necessary to enable the judges appointed for the purpose, to form a correct judgment of their respective merits.

Should several plans for any premium be proposed by the same person, a model of one, with accurate drawings and estimates of the others, will be sufficient: no individual to be entitled to more than one premium, where two are offered for the same object.

The judges will be requested to withhold" any of these premiums, provided no plans be brought forward, which they shall deem of sufficient importance to merit them; the premiums will then be continued to another year.

Competitors for the foregoing premiums are requested to send their plans, &c., free of expense, to the secretaries, one month before the next exhibition, of which due notice will be given.

Charles Fox, Esq., offers to the society, as long as he continues a member of it, the sum of four pounds annually; to be distributed in the respective sums of two pounds, one pound, twelve shillings, and eight shillings, in four several prizes, for the neatest, and most correct maps of some one state, province, or European colony, comprising not less than 144 square miles; or a portion of not less than 100 square degrees of some uncivilised region.

These prizes to be called the Lander Prizes, in commemoration of those enterprising travellers, Richard and John Lander. The principal rivers, lakes, chains of mountains, line of coast (if any), and territorial line, should be accurately delineated ; and the size of the most important cities, or towns, with their latitudes and longitudes, should be correctly marked. The maps should be accompanied by the fullest practical information (with reference to authority), either respecting the principal river flowing through the country, selected, as it

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