at the same time to be placed successively at uniform distances of 100 feet by means of the chain. It is scarcely necessary to observe, that the difference between an arc of 100 feet and its chord, on any curve which usually occurs on railways, is too small to cause any perceptible error in practice, even in a very long distance; but should curves occur of unusually short radii, it is easy to calculate the proper chord, and set it off from each stake to the next, instead of 100 feet, the length of the arc.

When the inequalities of the ground prevent a distant view from any three stations to lay down the entire curve from them, any stake which has already been placed in a commanding position will answer as a station for the theodolite.

By this method the operation of laying down a circular curve of any radius is made exactly analogous to that of laying down a straight line with the assistance of the telescopic sights of a theodolite.

It is stated that by this method the curve is laid down with accuracy at the first operation; that any accidental error in the position of a single stake, affects that stake only; and it has been found in practice that the progressively increasing errors of the old method are entirely avoided.

The

Mr. Gravatt observed that a well-made theodolite* was a convenient instrument for setting out curves for railways, and that it had been used by him and by his assistants for this purpose for several years. common theodolite was not, however, in practice universally applicable without some further contrivances for accommodating it to this peculiar service.

He stated that the circular arc (used, he believed, almost universally on railways) was not the true curve for a line of rails; as might be proved by considering that a straight line of road required both rails to be at the same level, when viewed in the cross section, whilst on a curved road the outside rail required to be raised, in order to resist the tendency of the engine and carriages to fly off the rails in going round the curve.

Where a straight line was joined on to a circular arc, the before-mentioned condition would require an instantaneous and vertical rise of one of the rails, which was a condition that could not be fulfilled.

In curves of contrary flexure, if composed

*Part of the curves of the north division of the Birmingham and Gloucester Railway were set out with the theodolite, by Captain Vetch, in 1836. And in 1837, that gentleman suggested to Captain W. S. Moorsom, the use of the parabolic curve as being theoretically the best, for railways, and of practical utility in sharp curves.

of circular arcs, the difficulty was increased; for the outer rail, which ought to be the highest, suddenly became the inner and the lowest, so that an instantaneous elevation of one rail, and a corresponding depression of the other was required; if the curves were of the same radius, the alteration would be of double the extent to that required when passing on to the same arc from a straight line.

Therefore as the outside rail must be in all cases the highest, the circular arc, which required the manifestly false condition of an instantaneous elevation, could not be the true

curve.

He had several years since demonstrated that the true curve was one, which commenced with an infinite radius, decreased in a regular manner, in advancing on the curve, when the radius might be constant for some time, and then increased again to infinity, before it joined either a straight line or another curve of contrary flexure.

He had fixed upon the elastic curve, which complied with all the conditions required, but other curves were also applicable.

His late assistant, Mr. W. Froude, had found that arcs of a cubic parabola, whilst they complied with the necessary conditions, were extremely convenient in practice; the equation and its fluxions, or differential coefficients, being very simple and easy of application.

Mr. Froude had also applied other properties of that curve, so that with the assistance of a few calculated tables, the process of setting out a true curve was rendered as easy in practice as setting out a circular arc. With any curve there was considerable practical difficulty in finding the direction of the tangents, the radii of curvature, and the position of the curves upon the ground.

Mr. Gravatt used what he termed a skeleton plan, of several stakes driven into the ground nearly in the course of the intended line, expressing their position by columns of figures with reference to two co-ordinates; thus obtaining a numerical accuracy far greater than that of any drawn plan.

By using a table of sines and co-sines, a few hours' calculation would save many days' labour in the field, besides ensuring an accuracy not otherwise to be obtained.

sufficiently flexible for light loads. Its effect is to make the strength and stiffness of the spring increase in proportion to the load placed upon it. Each extremity of the spring, instead of supporting a shackle or roller, as in the usual construction, carries a small convex plate of cast iron. The form and position of this plate are so adjusted, that when the carriage is unloaded, it bears on the extreme end of the spring, thus allowing it to exert the greatest amount of flexibility; but as the plate is convex, the more the load increases, and the further the ends of the spring descend, the nearer does the point of bearing of the plate upon the spring, approach to the centre, or fulcrum, so that the convex plate or contractor tends to diminish the virtual length of the spring in proportion to the load, the result of which is to increase the strength of the spring, in the inverse ratio of its virtual length, and its stiffness in the inverse ratio of the cube of the same quantity.

The

The author then gives in a tabular form, the details and the results of some experiments made on springs of this description, which are similar to those now in use on the Edinburgh and Dalkeith Railway. springs were 4 feet long, each consisting of ten plates, each inch thick, and 24 inches broad. The contractors were cast with a radius of 12 inches, and so constructed as not to act until the load on each spring exceeded 10 cwt., and with a load of 30 cwt. they should have contracted the distance between the bearing points to 3 feet 4 inches, instead of 4 feet; by this means the strength of the spring was increased in the ratio of 6 to 5, and its stiffness in the ratio of 216 to 125.*

The advantages stated to be derived from the use of these springs on the Edinburgh and Dalkeith Railway, and other lines, are

That they afford the same ease of motion to a single passenger as to forty or fifty in one carriage; they save wear, both of carriages and railway track; they produce the strength and stiffness requisite for the maximum load with less weight of metal; they are not more expensive than rollers; and they are not offensive in appearance, indeed they would not be observed unless they were pointed out.

Since this communication was made, contractors of greater length and increased radius of curvature have been applied, so as to produce a contraction of 6 inches at each end of the spring when fully loaded, which increases the strength in the ratio of 4: 3, and the stiffness in that of 64: 27. The details of the construction of these contractors, with a drawing of them, as applied to the springs of the carriages on the Edinburgh and Dalkeith Railway, are given in the addendum to the original paper.

15

ELECTRO-MAGNETO PLATING. Sir,-In a letter which appeared in your Number of last week, containing an exposure of the common and fraudulent practice of appropriating and securing other persons' inventions by patent, mention is made of a patent, which is conspicuously held up as one of "the numberless instances in which parties obtain patents for inventions to which they have not the slightest foundation of a claim;" in reply to which, I beg the favour of the insertion of the following remarks.

The writer asserts that Mr. Sturgeon published an account of my magneto process of plating, &c., in 1842. To this effect, he quotes the following passage :-‘ "It is now more than seven years ago that I contrived a magnetic electric machine, by means of which I coated metals with tin, copper, &c.; and I have employed the same machine to advantage in gilding, silvering, and platinizing various kinds of metals of inferior value, and I have no doubt that in this capacity the magnetic electric machine may become generally useful. I have produced good electrotypes on a small scale by its employment."

As far back as the year 1834 I was engaged with my father in experiments with the magnetic machine, and had a large one constructed, by which we decomposed water, iodine of potassium, and other compound solutions, and were the first, I believe, to produce a continuous current by the magnet, which was never published beyond the lecture room of the Royal School of Medicine, of this town. Two years afterwards we applied the magnet to the decomposition of copper. In 1839, we used it in depositing silver from the ammoniacal solutions, with a view to plating; but our trials, although partially successful then, were not brought to that perfection requisite for practical purposes, until I accomplished this desideratum in 1841, and, at the same time, discovered a new class of solvents. I then applied for a patent, and owing to a patent being unspecified before mine, was advised to wait a few months, during which time Mr. Sturgeon published his work, stating that he did it, but without explaining and mentioning how he effected this object.

In answer to what "C. W." says-" If Mr. Woolrich had made some ingenious improvement in the magnetic-electric machine," I would refer him to my specification, and Mr. Sturgeon's account of his machine, a perusal of which will show that there is an essential improvement and difference between the two-the general form of both machines being taken from that of Mr. Saxton's, which was made in 1833. Some idea, I think, will be formed of the improvements

which I have introduced, when I state that I can construct a machine for about £15, which is capable of depositing 60 ozs. of silver per week; and hope still to reduce its cost considerably. Mr. Sturgeon's merit as an electrician, and his valuable assistance in the collateral branches of science, entitle him to the regard of every scientific person; but although, like others, he may have contributed to the advancement of this department of science, he certainly has not applied it, practically and beneficially, to the arts. It was for doing this that I obtained my patent. I am, Sir,

Yours respectfully,

JOHN STEPHEN WOOLRICH.

LIST OF PATENTS GRANTED FOR SCOTLAND,
FROM THE 23RD OF MAY TO THE 15TH
OF JUNE,
1843.

Charles Maurice Elizei Sautter, of Austin Friars, London, gentleman, for improvements in the manufacture of borax. (Being a communication from abroad.) May 23.

John Laing, of Dundee, Forfar, linen manufacturer, for improvements in apparatus for rubbing linen-cloth, when making in power-looms. May 23.

John Nisbett, of Elm-street, Long-lane, Bermondsey, Surrey, engineer, for improvements in preparing hides and skins in the manufacture of certain descriptions of leather. May 23.

Joseph Burch, of City Road, Middlesex, civil engineer and machinist, for certain improvements in machinery for printing on cotton, silk, woollen, paper, oil-cloth, and other fabrics, and materials, and certain apparatus to be used in preparing the moulds, and casting surfaces for printing, and for certain modes of preparing surfaces previously to the design being delineated upon them. May 23.

Angier March Perkins, of Great Coram-street, Middlesex, engineer, for improvements in the manufacture and melting of iron, which improvements are applicable for evaporating of fluids and disinfecting oils. May 25.

William Brown, of Glasgow, for improvements in the manufacture of porcelain, china, pottery, and earthenware, and which improvements are also in part applicable to the manufacture of paper, and to the preparation of certain pigments or painter colours. May 26.

Perceval Moses Parsons, of Stamford-street, Surrey, civil engineer, for certain improvements in steam-engines and boilers, and in motive machinery conneeted therewith. May 31.

Alfred Brewer, of Surrey Place, Old Kent Road, Surrey, wire-worker and felt manufacturer, for improvements in machinery for manufacturing paper. (Being a communication.) June 1.

Charles Clark, of No. 1, Great Winchester-street, London, merchant, for an improved pyro-hydro pneumatic apparatus, or means of generating, purifying, and condensing steam and other vapours, and of extracting from vegetable substances the soluble portions thereof; as also the application of parts of the said apparatus to other heating, evaporating, and distilling purposes. June 3.

John Tappan, of Fitzroy-square, Middlesex, gentleman, for certain improvements in machinery for preparing and spinning hemp and such other fibrous materials as the same is applicable to. (Being a communication.) June 5.

Joseph Beaman, of Smethwick, Stafford, iron master, for improvements in the manufacture of malleable iron. June 7.

James Boydell junior, of Old Farm Iron Works, near Dudley, ironmaster, for improvements in manufacturing bars of iron with other metals. June 7.

Robert Alexander Kennedy of Manchester, Lancaster, cotton-spinner, for certain improvements in machinery for grinding or sharpening cards used in carding cotton or other fibrous materials. June 7.

Martyn John Roberts, Esq., of Bryn y Caeran, Carmarthen, Esq, for certain improvements in machinery for preparing, spinning, and winding wool, cotton, flax, silk, or any other fibrous bodies. June 8.

Charles Hancock, of Grosvenor-place, Middlesex, artist, for certain improvements in printing cotton, silk, woollen, and other fabrics. June 13.

George Robins Booth, of Hanley, Stafford, manufacturer and chemist, for a certain improved mode of applying heat from various combustibles to manufacturing and other useful purposes. June 15.

The advantages of Wire Rope over Hempen ones. -Since the introduction of wire ropes in the mines of Saxony, experience has proved them to be more advantageous than hempen ropes, both in cheapness and in durability, which has warranted their general introduction into all the mines of Saxony. The price of the hempen rope of 288 threads is, to the price of the wire rope which replaces it, as 1 is to 0.3483; consequently, the wire rope is 65.17 per cent. cheaper than the hempen rope. The price of a hempen rope of 336 threads, the largest used in the mines, is in the proportion of 1 to 0.3405. Hence, the wire ropes are two-thirds cheaper than the hempen ropes which they replace, and, under many circumstances, of greater durability, particularly in moist situations, or where the rope remains for a long time coiled on the drum, when it decays from mildew. Besides these advantages, the wire ropes are one-third the weight of the hempen rope which they replace. Wire rope of twelve wires weighs, per lachter (equal to two French meters, or 78 6-8 English inches), 3.4309 pounds; hempen rope, of 288 threads, weighs 9.62 pounds, or as 0-3536 is to 1. The wire used is 3-3 milli-metres in diameter, equal to 039 inches, and the strength of the wire ropes is in proportion to the number of wires. The wear and tear of wire ropes is less rapid than by hempen ropes; consequently, the hempen ropes, to have an equal durability with wire ropes, must, at the outset, be much stronger. The maximum strength, or breaking strain, of hempen ropes of 288 threads, is, expressed in pounds, equal to 19,800 pounds; whereas, the breaking strain of the wire rope of twelve wires, used in the place of the above hempen rope, is, when new, 11,200 pounds. Wire ropes, having a much less elasticity than hempen ropes, must, consequently, be coiled on a drum of greater diameter. The result of the experiments made at Freiberg, is, that the drum for iron wire ropes must never be less than 8 feet in diameter, and the maximum of the working load must be between one-sixth and one-seventh of the breaking strain. Wire ropes have been in use since 1834 in the mines of the Hartz, and have been lately introduced at the coal mines of the northern counties in England, and on most of the railroads where stationary engines are used.-Freiberg Mining Journal.

INTENDING PATENTEES may be supplied gratis with Instructions, by application (post paid) to Messrs. Robertson and Co., 166, Fleet-street, by whom is kept the only COMPLETE REGISTRY OF PATENTS EXTANT from 1617 to the present time.