A Visit to the Royal Polytechnic Institution.
No sooner do we enter, and pay our shilling at the door, then “bang, bang, bang” goes the gong—a Lecture on “a New Method of Blowing-up Sunken Vessels” is announced. Do our young friends recollect the circumstance of the sinking at Spithead of one of our largest men-of-war, the “Royal George?” a very beautiful model of which is to be found in the Museum for Shipping and Maritime Apparatus; the circumstances are so well known, that we will presume you not to be ignorant. Well, some years after the accident, a plan was projected by Colonel Pasley, of the Royal Engineers, for raising the guns and other valuables which were, of course, carried down with the ship; this plan was founded upon the well-proved law of electricity—that if the wire which conducts that wonderful agent be intercepted by a short piece of platinum wire, exceedingly small in diameter, and placed within a membrane impervious to water, and surrounded by a charge of gunpowder, a partial impediment to the passage of the electric fluid necessarily takes place, and the small platinum wire is made red-hot—and my young friends well know that if a piece of red-hot wire be placed in contact with gunpowder, that it will readily explode; hence, if a sufficient charge be placed within the vessel, the explosion would separate the timbers of the ship, and, by their floating properties, they would rise to the surface, and leave behind any great weight, such as guns, &c.; by the aid of the diver, then, they are attached to air cylinders, and floated to the surface. But to accomplish this, there are many reasons why more simplicity should be employed, and for this purpose the Lecture we allude to was given, embracing as it does a more simple plan. The invention is patented by a gentleman named Trestrail, of Southampton, and is as follows:—An air-tight vessel is fitted up with a coil of “fuse,” as it is called, consisting of a kind of flexible tube filled with gunpowder, and coated with a pitchy substance, to prevent its coming into contact with the water, which would, you know, destroy its explosive condition. This fuse will continue to burn under water for almost any distance, and was formerly used for the purpose of blasting rocks, blowing up sunken vessels, &c.; but the adaptation of Mr. Trestrail differs from this method, from the material or fuse being in the case, which is to raise the object from the bottom, by generating the gases contained in gunpowder, which gases are nitrogen, carbonic oxide, sulphurous acid, deutoxide of nitrogen, and carbonic acid gas, in different proportions. But this is going from our subject—you must read Chemistry to understand this. However, these gases force the water from the cylinders, and of course take its place; then, you know that the specific gravity or weight of the gas is so much less than the same bulk of water, that it has a buoyant property and rises to the surface, bringing with it whatever, in the judgment of the diver, it is capable of lifting. Many thousand pounds’ worth of property is now lying at the bottom of the sea and rivers, which seems a pity when so simple a method can bring them again to “terra firma.” After this Lecture, which was illustrated in a large tank of water in the centre of the Great Hall of the Institution, we walked around to look at the immense collection of models of all new discoveries in science. There was the magnificent model of the Britannia Bridge.—The machinery, which commences by taking the cotton from the pod, cleans it from the seed by means of rollers; then it is passed through another instrument called a carding machine, being a series of wires so placed as to tear the cotton asunder, and lay it in a beautiful sheet on the surfaces of the wires; from thence it is collected by a most elegant and ingenious contrivance, formed into a fillet, and then placed on the roving frame; thence it passes into the spinning frame and becomes thread, which is again used in an exhibition of the lace manufacture, by a beautiful model machine.
In close proximity to this machine, we observe a model lighthouse, fixed on a black substance for its base: this substance is very curious, and requires a little explanation. In Trinidad, in the West Indies, there is a Lake of Bitumen. A stream of this Bitumen (which you know is a sort of pitch) flowed in distant ages, through a channel two thousand yards in length to the beach, and thence six hundred yards into the sea, carrying with it all the loose materials encountered in its progress. This now constitutes a promontory, whereon the action of the waves and atmosphere, under a tropical sun, have had no deteriorating effect. This fact led to investigation, and now it is used as foundations to lighthouses, piers, jetties, bridges, &c., as well as water-pipes, instead of lead, which you know will combine chemically with the constituents of water, and convert that water into a deleterious compound. When Admiral, the Earl of Dundonald, (to whom this pitch belongs,) was Commander-in-Chief of the West India Station, he made many experiments on this wonder of nature, and has patented its application to very many useful purposes; his lordship laid down, from the lake to the shore, a series of pipes, which were manufactured by his sailors, and which pipes enabled the ships on the station to obtain excellent fresh water, without the difficulty of carrying it overland, which, in that hot climate, would have been very inconvenient. These pipes have been found as strong as iron ones of the same admeasurement. It is also applied to the coating of the wires of the Electric Telegraph with great advantage.
On we go to the upper gallery, and find the gigantic reflectors for illustrating the laws of reflection of heat, light, &c., which, singularly enough, are governed by the same law; sometimes by these instruments a mutton-chop is placed in the focus of one of them, and at one hundred feet distant a fire is placed in the other; the result is, that the chop is cooked, or a candle may be lighted by the same means at the same distance: this is by reflection. Well, another bang of the gong, and away we go to hear a Lecture on “the Process of Marbling and Decorating Paper.” By-the-bye, that gong is a curious instrument, being composed of a large steel spring, coiled round in an open coil, and terminating in a standard. On being struck with a hammer it emits a melodious sound, like the tone of a church bell, for which it has been proposed to be used, and is patented for this purpose; and no doubt, in a short time, these instruments will be so improved and tuned, so as to do duty for a whole peal of bells. The Marbling of Paper has never yet been made public, the trade having carried the process on in perfect secrecy, so as to retain a monopoly—which is a very bad thing, as it prevents many improvements being made, which would much increase its sphere of utility; the simplicity of the process, however, has been now brought forward by the public spirit of a gentleman named Woolnoth, to whom the world should be much obliged for upsetting monopoly, and breaking down principles which tend to frustrate rather than accelerate improvements in science. The process commences by making a solution of the “gum tragacanth,” and which is called in the shops, “gum dragon;” this solution being brought to a proper consistency, is placed in a long flat vessel, sufficiently superficial to allow a large sheet of paper to be placed on its surface. Well, having prepared this apparatus, which requires great nicety, the workman, having his colours already mixed, sprinkles on the surface of the gum solution a sufficient quantity, first of one colour and then another, until he obtains the required pattern. But the philosophy of obtaining this pattern remains to be told. The colours are mixed with such materials as cause them to repel when they come in contact with each other, in the same manner as oil does when dropped on water. The material thus made use of is gall taken from the bladder of an ox. This substance has the curious property of preventing the colours from mixing with each other; for instance, if a sprinkle of lake be first put on the surface of the gum (there being no absorption of colour as there would be on paper,) and another colour having gall ground with it be sprinkled over this, the two colours, instead of mixing, would immediately repel each other, and form a curious pattern, each colour forming its own particular shape, and this may be carried on to any number of colours; it is applied to various purposes, such as covering copy-books, and the edges of books. For many years this invention was confined to the Dutch workmen, and the patterns produced by them are still called the “old Dutch patterns;” but an Englishman discovered the means by which this pattern was obtained, and by his ingenuity very much improved the application, and this improvement, although still suffering from the same secrecy in England with which it was encumbered in Holland, bids fair to develop many improvements, of which the public spirit of Mr. Woolnoth has rendered it susceptible. Based upon these circumstances, Messrs. De La Rue, the famous card-makers, set their ingenuity to work, and have produced such wonderful advantages, that the papers now introduced by them are perfect gems of art—the “iridescent film,” as it is by them technically called, giving on the surface of highly-glazed paper all the beautiful colours of the rainbow. It is singular, that if an exceedingly thin film of a gummy varnish be floated on the surface of the water, a sheet of paper placed thereon may be taken off, having all the splendid colours referred to. But to perfectly understand the process it should be seen, and this is easily done by a visit to that delightful place of recreation, the Royal Polytechnic Institution. So many are the attractions of this Temple of Science, that we intend to pay it another visit; and no doubt, from the constant additions which are daily made to the Museum, we shall find matter with which to entertain and instruct our readers; bearing in mind that while the brain is engrossed with useful things, there is no room for vicious and useless thoughts.
