a complacent negative on all attempts to improve what was either partially known, or imperfectly practised, some fifty years ago. Signor Pistrucci's first application of his new process, has been in striking up a seal for the Duchy of Lancaster. This seal is four inches in diameter, of sterling silver; one side presents a very beautiful equestrian figure of her Majesty, Queen Victoria, surrounded by a bold inscription; on the reverse, the arms of the Duchy are richly emblazoned, in the midst of a profusion of scroll-work, with an inscription. To have engraved the two dies for striking up this seal, would have taken about fourteen or fifteen months hard labour, with the risk at the end of that time, of the dies breaking in the process of hardening. By Signor Pistrucci's method, they have been produced in less than fifteen days! There is an exquisite softness, and a boldness of relief, in many parts of this seal not attainable in an engraved die; the graceful flowing of the drapery, the prominence of the arm of her Majesty, as well as the ear and hoofs of the horse, are altogether unrivalled. The fame of Signor Pistrucci's success has drawn to the Mint, most of those who are celebrated for their practical acquaintance with the powers and properties of the metals, and with mechanics generally; one and all of whom, have expressed themselves astounded at the results obtained. When such gentlemen as Bramah, Maudslay and others, state, that nothing short of seeing with their own eyes would have satisfied them of the possibility of such a work, incredulity may well be pardoned in those who have not witnessed the recent production. There are plenty of workmen in the Royal Mint, well versed in all the methods employed at the Soho for the last fifty years, and they all agreed in designating Mr. Pistrucci's plan, when first propounded to them, as a new fangled and impossible scheme, and yet have these very workmen themselves since proved its possibility. The outline of Signor Pistrucci's plan, is tolerably well explained, in the Times newspaper referred to; the subject is modelled in the usual way, either in wax, clay, or other fit material, from which a cast is taken in plaster of Paris. The plaster cast being hardened, is moulded in fine sand with great care, and a cast in iron is taken from it. The great secret— if there can be any secret in what has been published in the leading journal of the day, and thence very extensively copied into other publications-consists in the thinness of the iron castings. The plaster of Paris model is left only about one eight of an inch thick, the consequence of which is, that the chill which takes place on the surface of all iron castings, from the proximity of the two surfaces in this instance, pervades the whole mass, giving it the hardness of a hardened steel die, with a toughness, not attainable by the latter metal while in a hard state. In all large castings, the contraction of the mass of metal in cooling causes a shrinking of all the finer lines, while in thin castings, the sharpness of every line is preserved with suprising beauty. Mr. John Baddeley says, "it is utterly impossible to cast any metal hard enough for the purpose in sand or loam or any other composition!" Verily, Mr. John Baddeley is but a poor authority in such matters-facts prove him wrong. Signor Pistrucci is his own founder, but there is no peculiarity in his mode of foundingnothing beyond the extreme care, which the delicacy of the subject in hand requires; his castings do him much credit, though they are by no means equal to the productions of the best Berlin casters. The iron casting having been made perfectly flat at the back, a hollow is turned out in a steel bed to receive it, and when thus mounted it is ready for use. One proof among many others, of the extreme hardness of the cast-iron dies, is afforded by the fact, that no extension of the metal takes place from the severest blows: the die fitting no tighter into its bed, after striking up medal, than it did before. The seal before alluded to, took upwards of one hundred and fifty blows from the most powerful press in the mint, and the dies appear in every respect as perfect now as when first cast. Many persons, who, from their known celebrity and eminence in the scientific world, would be considered the very highest authorities that could be cited in a question of this kind, have not only on examination admitted the entire novelty and great importance of this process; but have charged Signor Pistrucci with injustice to himself, for neglecting to secure the privileges of a patent. This, however, the Signor has from the first declined to do; choosing rather to throw open the result of his (miscalled) "hours of idleness," for universal public benefit. What the real value of this discovery is-or where the useful application of the fact thus established will stop, it is at present wholly impossible to imagine. The advantages, of being able to produce at so little cost, and in so short a space of time, the most perfect and beautiful designs-or to copy with so much facility the choicest productions of others, are altogether incalculable. One drawback, perhaps, is the power thus placed in the hands of the fraudulent copyist, and the spurious coiner; but the knowledge of an existing power to do certain mischiefs generally produces an antidote sufficient for the evil, and it is to be hoped the present case forms no exception to the rule. One happy effect of the general introduction of this method of obtaining dies, will be, to make the die-sinkers more of artists and less of mechanics, to wield the graver less but the pencil more skilfully. Should my endeavours to render this useful process intelligible, not be sufficiently explicit I shall have much pleasure in affording any additional information that may be thought necessary, but as this communication has extended beyond a convenient limit, I shall for the present close, by subscribing myself, Your's respectfully, London, April 6, 1838. WM. BADDELEY. PREVENTION OF FIRE ON BOARD SHIPS AT SEA. Sir,-On reading the remarks of Mr. Baddeley, in your last Number, relative to the late fire on board the "Great Western," it occurred to me, that still further precaution might be taken to prevent the spread of fire on board steam-ships at sea, by having a smokeproof jacket, such as is used by the London Fire Engine Establishment; the engine-room might thus be entered when full of smoke, and a forcing pump put into work, which it appears could not be done in the case referred to. An arrangement by which the engines would be as controllable on deck as in the engine-room, might also be useful in some cases of emergency, precaution heing, of course, taken to prevent any except the engineers having access to the small space allotted for this purpose. When two engineers and several stokers are employed, they should not all be permitted to remain in the engineroom at one time, or we may witness a repetition of the melancholy scene on board the Victoria, when every man(if I am rightly informed) who was capable of assisting in any way in the engine-room-was suddenly deprived of the use of his limbs. Had one-half of these unfortunate men been on deck, there would have been a saving of human life, and of labour, which at sea, is unquestionably the most valuable. I am, Sir, Your obedient servant, 20, Maiden-lane, Wood-street. PORTABLE SHIPS' PUMPS. Sir, Mr. Baddeley, with his characteristic zeal, has lost no time in calling attention to the fact, that even the untiring energy of the steam engine cannot at all times be availed of on ship board, for the purpose of extinguishing fire, although fitted with apparatus which might be instantly adapted for that purpose. The advantage of an auxiliary pump on deck has been clearly shewn in the instance of Merryweather's engine on board the "Great Western," and it would be well if every sea-going steam vessel were similarly supplied. In addition to the pump worked by the engine, many vessels are fitted with Downton's rotary pumps, which are fixed on deck, and efficiently perform the several offices of fire engine, bilge, fresh, and salt-water pumps; and each may be adapted by a very simple and expeditious contrivance: but still, in case a fire were to take place in the neighbourhood of the pump, its valuable services would, in all probability be cut off. A very compact portable pump was constructed some years since, by Mr. W. Kingston, engineer, at Portsmouth, and with very slight exception, resembling that since patented by Hearle, of Plymouth. This pump has two barrels concealed in a snug iron box, leaving only the two ends of an axis protruding, on which the handles are shipped for use, in the manner of an ordinary fireengine the box becoming the air vessel;-the whole is fixed on a plank, which may be placed on the thwarts of a boat, and is transported with great readiness. This pump can wash decks, wet sails, water the ship from alongside, or become a bilge pump if needful; and when watering on a dangerous coast, by mooring the boat without, and leading the hose on shore, the casks can be filled in place without the risk attendant on getting them off through the surf. As to its advantages as a fire engine, I was witness to an alarm of fire on board a vessel in harbour at eleven at night ;the crew was roused and the pump got over the side into the boat and alongside the vessel in danger, in ten or fifteen minutes from the outcry; fortunately the fire was smothered below, in time to prevent a conflagration. On another occasion, when a steam vessel was approaching her anchorage, on a still night, after a voyage of some days, the ignited soot was seen to pour out from her chimney so as to resemble a volcano, driving her crew off the deck, which they were flooding with water. The engine was instantly got out and sent to meet her, the hose being shipped during the time; but her assistance was again rendered unnecassary from the precautions taken on board the steamer. I mention these facts, although, perhaps tedious, in order to show that the advantages of portable engines are by no means limited to the ships they are on board. In the cases above stated, there was not one of the many vessels in the port, excited by the alarm of fire, which could bring any thing but a bucket into play. How efficient would the crowd of boats, at a distance from the shore, have been rendered, had each had a portable fireengine on board! Hearle's pumps are now manufactured by Mare, engineer, at Plymouth, who could best describe them and their capabilities. I am, Sir, &c. Woolwich, April 9, 1838. NAUTICUS. MIXTURE OF SULPHATE OF BARYTES WITH WHITE LEAD. Sir, I beg leave to address the following query to your scientific correspondents through your widely-extended miscellany. Is sulphate of barytes a fit and proper ingredient to be mixed with white lead for paint? An immense quantity of this article, which does not possess the viscous properties of white lead, is ground in Montgomeryshire, North Wales, and sold in England, as well as a considerable quantity sent to America, at an immense profit to one or two parties. The colour and weight of the ground material so nearly resemble white lead, that it is difficult to discover the difference when mixed with it. If this article be not proper to mix with white lead, how may its presence be detected? NO PAINTER. Solop, April 12, 1838. RIDDLE'S UNIVERSAL PEN-HOLDER. It is highly amusing to observe the gradual progress of invention, to watch the steady progress of improvement as it advances step by step towards perfection-to see plans and contrivances that have long reigned pre-eminent, set aside one after the other by the every day "march of science." Scarcely a number of our Magazine issues from the press that does not teem with numerous instances of this description; upon the present occasion we have to notice a new Pen-holder, lately introduced by Mr. G. Riddle, whose intimate connexion with most of the improvements in writing materials for the past fifteen or twenty years, must be well known to many of our readers. The jointed pen-holder patented some some years ago by Mr. Bramah, hitherto the best extant, is too well known to require description, having been very extensively employed for a long time; its construction displayed much ingenuity, the smiths' tongs being its model; but the mode of application rendered this principle liable to many inconveniencies and objections. Bramah's holder was only adapted for pens of an elastic character, or of an uniform curve and thickness; the insertion of a large or thick pen caused a straining of the joint which prevented its holding a thin pen ever after. There was also considerable difficulty in guiding the slide-ring over the sharp pointed tail-piece, and as this tail-piece must always be brought close down upon the body of the tube to al-low the ring to pass over it, whatever the size or curvature of the pen-the straining before alluded to was the inevitable result, which ended in the breaking of the holder. Various attempts have at different times been made, to simplify this holder and preserve its good qualities, but without success-all these attempts having been even more objectionable than their prototype. The last effort, however, now before us, is an exception; Mr. Riddle's universal penholder is a very simple and effective instrument adapted for either quill or metallic pens, of various curves and thicknesses. This new and highly ingenious contrivance combines all the excellences of previous inventions, and at the same time, obviates the several objections to which they have been liable. The construction of the universal pen-holder (so called from the extensive nature of its application,) will be readily understood by referring to the accompanying engravings, where it will be seen to consist of a gold or silver tube, with a handle of ebony, ivory or other suitable material; on the under side of the tube, which is semi-cylindrical for a short distance up, there is a detached limb held by a strong spring-joint exerting a constant tendency to keep the jaws of the holder apart, as shown by fig. 1. This tendency is counteracted at pleasure, by a sliding ring, which being pushed towards the extremity of the holder, brings the jaws together until they are so closely in contact, as to embrace and hold very fast any thing that is placed between them. The appearance of the holder with a pen mounted for use is exhibited in fig. 2. A very slight examination will suffice to shew the great superiority of this, over all preceding pen-holders. The pen, which may be of any ordinary size, is inserted without any trouble and without inking the fingers; when placed, it is held very firmly, but can never become fixed, as on withdrawing the ring the holder flies open and the pen is instantly discharged. The joint, which in other holders has always been the weakest part-in the above is actualy the strongest. Any variation in the size of the pen, is met, by a proportionate shifting of the fulcrum. This pen-holder has been pronounced by competent judges, in point of simplicity, durability, and convenience, decidedly the best hitherto produced. METHOD OF DRAWING THE PARABOLIC CURVE BY AN APPLICATION OF THE DESCENT OF FALLING BODIES. Fig. 1. Fig. 2. these divisions are intended to represent any given intervals of time. rbrare two narrow slips joined together at b, forming a right angle, and attached at the angular point to the middle of the slip ss, by a screw at the centre on which it turns; the slip s on being moved in either direction, will carry the right angle with it, the upper part of it sliding through a short at t, which is attached to a slider which moves in the groove af, and can be placed in any given position between a and f; the tube can be detached from the slider when required, and it also turns on its centre, that it may conform to the angular motion of the right angle. To represent the spaces that any body has fallen through in any given intervals of time, slide the slip s till the angular point of the right angle |