whereas, with paddle-wheels, the sailing power (from the cumbrous nature of the paddle-boxes and the immersion of the lee wheel, with the wind abeam,) is of little value. 6th. The weight of the propeller is not one-tenth of the paddle-wheels and their boxes. 7th. The beautiful appearance, and snug and safe rig of a sailing vessel is preserved by using the funnel as the mizen mast. 8th. A saving of nearly 20 per cent. in first cost, when equipped and ready for sea. 9th. A saving of at least 50 per cent. in disbursements. 10th. Room for carrying nearly double the amount of passengers and cargo, thus increasing the returns cent. per cent. 11th. The power of instantly disconnecting, shipping and unshipping, the propeller. From all the preceding advantages it can require no argument to prove, that the time has come, when vessels, worthy the name of ships (and not boats, as the present race of steamers are properly denominated,) may be usefully and economically employed in carrying her Majesty's mails with safety and despatch; and that we may now use steam, when necessary only, that is to say, in adverse winds or calms, retaining therewith the capability of laying aside steam, and using the old-fashioned and cheaper power, "the winds of heaven" whenever they blow from the right quarters, instead of being compelled, in such cases, to consume our fuel and work our engines for no other purpose than that of preventing the inactive wheels from performing the office of a drag to the vessel's sailing velocity. I am, Sir, your obedient servant, 2, Cowper's-court, Cornhill. H. WIMSHURST. DR. MOSER'S DISCOVERIES IN PHOTOGRAPHY, AND NEW THEORY OF THE PHOTIC FLUIDS. Sir, The account published in your Journal, of Dr. Möser's photographic experiments, is highly interesting to me, as indicating the approach to the recognition of the existence of photic fluids. It includes, I think, what Mr. Hall has termed "Thermography," namely, the novel phenomenon noticed by Dr. Möser, 66 that any two bodies, when sufficiently near, impress their image one on the other, although both be in absolute darkness." Having devoted many years to the endeavour of tracing the connexion of photic matter with the elements, I beg leave, on this occasion, to submit to your readers the following general observations. The only clue which I have been able to find to the chemical affinities of the inorganic elements, capable as they are of attracting, reflecting, and conducting heat, and of undergoing manifold atomic metamorphoses without destruction, is the hypothesis, that they must respectively consist of congerated inert radicals, chemically saturated with such proportions of imponderable, yet material photic fluids, as certain laws of nature allowed them to bind or appropriate to themselves, so as to constitute the existing diversity of apparently simple elements, while the very same fluids also abound in a vivid state. We cannot any longer doubt that the photic sunbeams are fraught with radical elementary matter, similar to the chemical flame of terrestrial fire, but much sublimer and purer; and we may be justified in presuming that they deposit such radical matter on the terrestrial globe, saturated with photic fluids, capable of being fixed in a process of condensation, after contamination with terrestrial effluvia. We have next to consider that the terrestrial globe, with its gaseous atmosphere, is encompassed by a subtile universal ether, and may fairly assume that the latter pervades the whole ponderable and porous elementary mass. This omnipresent ether must be an inert imponderable fluid, itself saturated with the still finer photic fluids, diffused through it by the sun, and is thus their omnipresent conductor, preserving a vivid store, always ready to act upon the ponderable elements by affinity with their fixed photic constituents. Such I presume to be the constitution of our earth and all the planets, subject to the regulative and fostering influence of the sun. The photicated ether in question, which I presume to pervade all nature, has not yet been recognized as being identical with the fine fluid contents of what we term vacuum. I consider that it is identical therewith; and if the atomic theory be reduced to the plain proposition, that all ponderable matter consists SAND TAMPING. of vesicular, more or less porous, perforated and elastic molecules, however minute and singly invisible, some being more expansible than others at a given temperature; it is reasonable to assume also, that, whether contracted or expanded, their central vacui, as well as the interstices between the atoms, must be replete with the said photicated ether, on the same principle on which air would replenish and encompass a heap of any hollow, perforated, and elastic globules. I have further come to the conclusion, that positive and negative electricity, positive and negative magnetism, are identical with four distinct photic fluids, discernible under certain circumstances, particularly in the body of a flame, by the blue, red, yellow, and the colourless or water hues, while the analysis of the sunbeams also exhibits negative (black) and positive (white) rays. We should thus obtain six distinct photic fluids, of which the last named two have no polarity in combination, but do alternately precede or lead, and may absorb the first named galvanic four. Let us also postulate, that in combination with the ether, positive electromagnetism constitutes latent heat, and negative electromagnetism-latent cold, and we may finally infer, that a concentration of the former around a combustible, or in the galvanic spark, is the radiating and conductible heat (diffused by gaseous fire or flame) by which organic bodies are dissolved their ponderable atoms being separated, expanded or rarified, rendered volatile and caused to float about, until refrigerated and recontracted by contact with cold, so as to reconstitute themselves into inert elementary congeries. The heated ether is thus in the expanded atoms, what gas is in a balloon or air in a bladder. There is more latent heat in a vacuo, than in the air surrounding the receiver; and gases, when compressed, evolve heat-some also say, light. The formation, growth and putrefaction of organic bodies is effected by slow atomic vibration or combustion at a low temperature; this process is incessantly going on in nature; it is the destiny of what we call matter. The laws of this process involve the important, yet unsolved question of elementary destructibility, which I do not wish to touch now, as it would lead me too far. On the same principles, darkness would be owing to a vivid predominance in the 7 ether, of negative-brightness or radiancy a predominance of positive, photic fluids. Whichever order of fluids is predominant, combats and repels the other, absorbing and neutralizing a certain residuum, so that neither is under any circumstances totally absent. The sun's radiance is a constant emanation and a re-attraction of chemical electromagnetic currents, retransmitted from the surfaces of the planets, in whose atmospheres they cause atomic vibration or undulation with brightness. In the sunbeams travelling along, their positive ingredients are foremost, the negative following in the wake; when hitting their object, they combine and intermix; the surface, the globe, absorbs less of the former than of the latter; thus a greater proportion is thrown back of the positive than of the negative, to cause atmospheric heat and undulation. By concentration of the sunbeams in burning glasses we have learnt to obtain solar fire; this was the first, and I deem it the greatest of the great discoveries that have been made down to photography, by which it is now proved, that all material bodies have constant photic halos of their own, radiating even invisibly and insensibly, "in darkness as well as in brightness," and capable of making impressions upon each other. This can only be owing to the affinity between the fixed photic ingredients of the elements and the vivid omnipresent photicated ether. And what does the polish of metals, the brilliancy of precious stones bespeak? If you can kindly spare a page in your valuable journal for this letter, you will greatly oblige, Sir, your most obedient servant, London, December 31, 1842. SAND TAMPING. Z. Sir,-In the November Part of the Mechanics' Magazine I perceive that a correspondent, J. F. B., is still of opinion that sand cannot be used for tamping. I beg to mention, for the information of others, that I have most successfully used sand for that purpose. The experiments have been tried in a stone-quarry. A hole, 2 inches in diameter and 5 feet deep, was made in the rock. Half the charge was first put into the exploding cartridge, and next the remaining half of the powder; then a tight oakum wad was put down, leaving a space of 5 or 6 inches between it and the powder: the hole was filled up with fine dry rabbit sand, to the depth of 15 inches. The sand was not blown out, and the result was quite satisfactory. The battery I make use of consists of 48 pairs of copper and zink semicircular plates, 8 inches in diameter: the plates are fitted to a suitable frame, with eight wooden discs, with rails mortised into them to support the plates. Through the centre of the wooden discs passes a strong wooden axle, which rests on the ends of the wooden trough, and only allows the plates to be within half an inch of the bottom of the trough. By turning a handle, the axle and plates are made to revolve, and can be immersed in the acid, or turned out of it, with the greatest facility. I remain, Sir, your obedient servant, H. M. Wexford, December 28, 1842. x=y and ab=ba. Q.E. D. Which reasoning may evidently be extended to any number of factors. I hope I am not intruding in addressing these lines to you; if I am not, I may perhaps take the liberty of addressing you again, from time to time, on similar subjects, offering more difficulties to the student who is beginning pure mathematics, and some of which he may be unable to surmount without the aid of a master. I cannot help being of opinion, that the important science, which a a a 1= y ; whence, is the only solid foundation of the sub- I have the honour to remain, Sir, A LOVER OF SCIENCE. City, December 24, 1842. Practical Conclusions in respect to Tubular Boilers. [From Memoir in the Journal of the Franklin Institute, by Benjamin H. Latrobe, Esq., C.E.*] Upon the 14th of April, 1842, the Medora, a new steam-boat, built by a company, to run between Baltimore and Norfolk, was prepared for a trial trip down the Patapsco. She lay at the engine-builder's (John Watchman) wharf, on the south side of the Basin. * The original of this very interesting memoir is illustrated by a number of very accurate engravings; but, as the parts here extracted by us are sufficiently intelligible without them, they are omitted. -Ed. M. M. Her fire was lighted at about 2 o'clock, p. m., and about an hour after, the agent and some of the proprietors came on board, and she prepared to start. There were probably between 50 and 100 persons in her when she started, many of whom were workmen connected with her construction; and as on such occasions these persons, each deeming himself to be magna pars of the affair, are prone to intermeddle, there was much crowding and confusion about the en EXPLOSION OF THE AMERICAN STEAMER MEDORA." gine, and its proper management by the engineman was not unlikely to be interfered with. The pride of the workmen in the expected performance of the boat would naturally dispose them to do all they could to accelerate her speed; and the suspicion afterwards expressed, that undue means were employed to increase the pressure of the steam, was not unreasonable. It has also, indeed, been supported by sufficient testimony, though at the same time contradicted, I am told, by one of the surviving witnesses of the calamity. The boat had just cast off her lines, and, in backing out, had made one or two revolutions of her wheels, when her boiler burst. Five-and-twenty persons on board were killed or mortally wounded; the upper, or promenade deck, over the boiler, was blown in fragments into the air, and the forward part of the hull so shattered, that she immediately sunk, in ten or twelve feet water. Her engine, except in its connexion with the boiler and the after part of the hull, was uninjured. The boiler was placed forward of the wheel-houses, standing fore and aft in the hold of the vessel, and rising up through the main, to within three or four feet of the upper deck. It was thrown upwards to the height of the top of the engine-beam, or more than thirty feet, and while in the air it turned, so as to fall upon its side, exactly crosswise of the boat. Circumstances connected with the escape of the steam and water, and the resistance of the wood-work of the upper deck, no doubt, caused this singular rotation. The boiler consists of a cylinder eleven feet in diameter, and nineteen feet long, supported on three legs, of the same horizontal length, and composed of sheets of five and a quarter inches apart, connected, as usual, by staybolts. The side legs are about seven feet, and the middle leg two and a half feet high. To admit the water into these legs, the cylinder, or belly of the boiler, is cut away by rectangular apertures at frequent intervals. The lower half of the cylinder is occupied by forty-seven tubes, eight inches in diameter, through which the smoke and flame are returned forwards, from the chamber at the back of the boiler towards the chimney in front. Between and above the rows of tubes were round tie-rods, threefourths of an inch diameter, horizontal and crosswise to the cylinder; but similar rods could not be introduced vertically between the tubes, on account of the spaces between them not coming in a line over each other. Thus, the top and bottom of the cylinder were not stayed by direct ties connecting them in the position of chords; but the top angles at either end of the boiler were braced 9 by diagonal bars and rods, and above the tubes were one or two rows of longitudinal rods, of one inch diameter, going from the forward to the after head. The sheets of the boiler were of the usual thickness of onequarter of an inch, and do not appear to have been of bad quality. There were two fire-doors in front, for the introduction of the fuel into the spaces between the legs; and in the sheet-iron composing the front of the smoke-chamber supporting the chimney stack, there was a small, movable, circular door opposite each tube, for the insertion of an instrument to clean the flues when required. The number of gauge-cocks was four, the lowest being a little above the level of the highest row of tubes. The safetyvalve was placed upon a drum near the top of the boiler, and was, as will be seen hereafter, of large dimensions. Such was the boiler in all its parts; and its unusual size and bold design must be striking to every observer. An examination of the wreck of the boiler, as it still stands in the yard of Mr. Charles Reeder, engine-builder, clearly shows that it first gave way where the legs unite with the belly, and where the removal of so much of the metal reduced the strength of the cylinder to its minimum. The explosion was downwards, carrying away the right-hand, or starboard leg, and the middle one, and tearing into shreds the inner sheet of the larboard leg, at its junction with the cylinder. The escape of the steam and water, principally on the starboard side, probably caused that side to revolve vertically in the rise of the boiler into the air, and thus would have made it fall upon its larboard side in the descent, while at the same time a horizontal revolution was effected by the forward rush of the expelled fluid towards the angle made by the front and starboard side, this part of the front appearing to be pushed outwards. The boiler evidently fell first upon the hind and upper larboard corner, which is seen to be much crushed, while the explosion operated most powerfully on the front and lower starboard corner. These two corners are diagonally opposite to each other, and this circumstance may account, (in connexion with the entanglement of the boiler in the fragments of the upper deck,) for the rotation. As the boiler lay in the hold on its larboard side after the explosion, the starboard and middle legs, together with the portions of the cylinder between them, were not entirely detached, but were so far bent backwards, and curled over, as to embrace the circular top; and, previous to the raising of the boiler out of the sunken hull of the vessel, they had to be separated by the chisel. The cutting of the apertures over the legs, in the manufacture of the boiler, to admit the water into them, left the segments of the cylinder, between the legs, united only by the strips of sheet metal remaining, and of these strips not more than one-half the original number are left, the rest being carried away by the explosion. The other injuries received were partly due to the rupture, and partly to the fall of the boiler; and the numerous and extensive rents manifest the insufficiency of the opening first made, though large, to vent the confined fluid, and that the destruction, once begun, proceeds ad libitum, as in almost all similar cases. The construction of the boiler, and the manner of its destruction, having been thus described, I proceed to estimate its strength from the data I have procured, together, and in comparison, with the probable pressure of the steam at or near the time of the explosion; and to state the facts of which I received information, respecting some of the circumstances of the accident, accompanied by such remarks as have suggested themselves to me, in regard to its causes and effects. The weakest part of the boiler, to which the calculation must evidently be applied, was manifestly the part of the cylinder immediately over the legs, where the continuity of the sheets was interrupted by the apertures made in them to let the water down into the legs, and promote its circulation throughout the vessel. One-half of the strips of iron left between these apertures has been carried away, and the measured width of those that remained is irregular ; but there is enough to show that the united breadth of all the strips did not exceed that of the spaces between them, so that the boiler was not more than half as strong over the legs as elsewhere, ceteris paribus. Thus, in every twelve inches of the length of the cylinder there were but six inches of sheetiron to unite the segments separated by the legs. A further reduction of strength, in the connexion of these segments, was again made by the occurrence of seams in the strips, depending on rivets, and weakened by the holes punched for their insertion. Now, the strength of a joint of this kind will depend upon the resistance of the rivets, and also on that of the remaining iron of the plates which they unite; which resistances should manifestly balance each other, to give the maximum of strength to the joint. The plates may be separated in three ways: 1. By cutting off, or tearing asunder the rivets, or tearing off their heads; 2. By splitting and tearing out the metal between the rivet holes and the edge of the sheet; 3. By tear ing off the sheet-iron between the holes, and in a line with their centres. That it may be indifferent, so far as dimensions are concerned, in which of these three ways the joint may separate, there must be certain fixed proportions between the diameter of the rivet, (the head of which we will suppose to have always such an excess of strength, as to make the shank of it give way first,) the clear distance between the rivet holes and the edge of the plate, and the clear distance between the holes themselves, the thickness of the sheet being, of course, a constant element. Let us now see whether, in the riveting of the sheets of this boiler, the correct proportions were observed. 1. The rivets are eleven-sixteenths of an inch in diameter, and each has a transverse sectional area of 0.375 of a square inch, and, there being three rivets to every strip of six inches wide, the whole area of the rivets will be 1.125 square inches; 2. The line of metal left between the holes will be (6-2·062)= 3.938 inches wide, which multiplied by onefourth of an inch, (the thickness of the sheet,) will give an area of 0.985 of a square inch; 3. The clear distance of the holes from the edge of the sheet is one and a quarter inch, which, multiplied by onefourth of an inch, gives an area of 0.312 of a square inch, and for the three holes, a total area of 0.936 of a square inch. The three resistances appear thus to be somewhat unequal, that of the rivets being the greatest, by 14 per cent., of the strength of the metal between the holes, and 20 per cent. of that of the metal between the holes and the edge of the sheet. But when it is recollected that in the first case the rivet loses part of its whole strength by the strain it suffers in cooling, after being headed in a heated state, and that in the third case the tearing out of the metal involves more than the mere separation of the area of resistance, inasmuch as to permit this, the metal must be considerably bent on either side of the line of rupture through which the rivet makes its way out, and as furthermore, the friction of the lapping surfaces of the plates augments their opposition to a separation by sliding on each other, it would seem as if the three resistances were very near to a practical equality, and that the sizes, numbers, and positions of the rivet holes were about what they should be, for the required equilibrium between the parts of the joint. Other boilers which I have examined show a similar adjustment of parts in the joints, so that the general practice would seem to accord with the conclusions of the present calculations. An inspection of the manner in which the plates of the Medora's boiler separated at the seams, showed that, in most instances, the |