By adopting this plan not only will the numerous heading joints (a sure source of weakness) of the present method be avoided, but the material itself will be, I conceive, considerably increased in toughness of fibre, as small wires are stronger in proportion than large ones. The planks should (I think) be annealed after rolling. Ships constructed with Iron Planking, well put together, (especially if the joints can be fused firmly together, of which, from Mr. Spencer's experiments, there can be little doubt,) would, I conceive, be almost invulnerable, and perhaps had the ill-fated Brigand been so built, she would have been afloat at this hour.

Should you think this invention, (if, indeed, invention it can be called,) worth communicating, you will do me the favour to insert it in your very useful Magazine, and so oblige your obedient servant, JOHN DAYMAN.

Mambury, Bideford, Devon, November 11, 1842. [The correspondence mentioned in a P.S. to Mr. Dayman's letter, we shall be glad to receive.-ED. M. M.]

IMPROVEMENT IN THE CONSTRUCTION OF CISTErns.

Sir, The remarks of Mr. Cole in a recent Number of your Magazine on the defects of our water cisterns, will no doubt draw the attention of ingenious men to the best means for their removal, which may eventually lead to the introduction of some important improvements in these articles.

In the mean time, I beg to offer a few remarks illustrative of the inattention hitherto paid to this matter, and to suggest a simple alteration of form, which would greatly increase the facility of cleansing, when this process is, as at times it always will be, absolutely necessary. Fig. 1.

Fig. 1, is a rough sketch of the manner in which cisterns are usually constructed; a is the supply pipe and ballcock; b the service pipe, or tap, fixed in the side of the cistern a few inches above the bottom; c the waste pipe, the plugsocket of which closes an aperture in the bottom of the cistern. The principle aimed at in this mode of construction has been, to allow all the ponderable impurities to become deposited at the base of the cistern, below the point at which the supply of water for domestic purposes is drawn off; the accumulated impurities being got rid of, by withdrawing the waste pipe. It unfortunately happens, however, that the object in view is often lost sight of by the cistern maker, who makes them in this manner, because he was taught so to do during his apprenticeship, and not because he comprehends the principle. In the greater number of instances it will be found, that the waste-pipe socket is soldered into its place in such a manner, that there is a considerable rise all round the opening, which ought to be, on the contrary, the lowest part of the cistern. Again, from want of care in the fixing, it will often be found that there is a fall away from, instead of towards this opening. In several cisterns I have noticed an elevation in the middle and a fall towards both ends. In all these cases it becomes a very troublesome, and a very difficult matter to effect the perfect cleansing of the cistern, as the water cannot all be run off: the impurities settle in the lowest parts, and fresh quantities of water thrown in, dilute but do not entirely remove them.

may be either of a prismatic or conical form; in either case, all the impurities, will settle around the waste wipe and be carried off by the rush of water towards the opening, whenever the waste pipe is withdrawn, and any further quantity of water thrown in will cleanse the cistern of every impurity. In the present form of cistern (fig. 1,) the escape of the water is sluggish; in the form suggested (Fig. 2,) its escape would be exceedingly rapid.

Fig. 3.

Fig. 3 exemplifies this principle as it might be advantageously applied to cisterns of slate. In this material, the bottom may be flat, but it should be made to incline from three of the corners towards the fourth, where the waste-pipe should be inserted. It is a very common practice to put up slate cisterns without any waste-pipe at all, but this is decidedly bad, because however cleanly the material of the cistern, impurities will in the course of time become deposited therein and must be removed.

In each of these cases it will be seen that the principle of drawing the supply of water from above the lower strata, is equally carried out, with this advantage, that if the cistern is emptied to this level the remaining quantity of unchanged water is a minimum.

I am, Sir, yours respectfully, WM. BADDELEY. Hamburgh, November 1st, 1842.

from a true guide. The name has been chosen from this circumstance, as expressing the peculiar feature of the invention. The thread produced is not only true, and of the exact pitch required, but perfectly formed throughout, being cut clean without distortion of the metal.

In all these respects the advantage of the Guide over the common Stock is remarkable. The latter, it is well known, will not cut a screw in any degree perfect. The thread, besides being irregular, is never of the right pitch. It is also more or less swollen by the violence done to the metal, so that the diameter of the screw is often considerably greater than that of the blank shaft on which it is cut. These defects are attended with the most serious practical inconvenience. They often render it extremely difficult to obtain a fit between the screw and nut, and consequently occasion a considerable sacrifice of time and labour. They necessarily impair in a very great degree the efficiency of the screw bolt, which cannot possess either the strength or mechanical power which it would have if the thread were cut true and clean.

The defects in question are variously modified according to the size of the master tap used in cutting the dies. If they have been cut by a master tap double the depth of the thread larger in diameter than the shaft to be screwed, they will act very well at first, and the thread will be started true, but as the operation proceeds, they become altogether unsteady and uncertain in their action. If, on the other hand, they have been cut by a master tap of the same size as the shaft to be screwed, the thread is made untrue in its origin. They first touch the shaft only on the extreme points of their outer edges, as shown in the following sketch.

DESCRIPTION OF THE MESSRS, JOSEPH WHITWORTH AND CO.'S PATENT GUIDE SCREW STOCK.

(Communicated by the Inventors.)

The Guide Stock is entirely new in principle, and will cut a screw scarcely inferior to that obtained in a slide lathe

They have neither sufficient guide nor steady abutment, till the operation is on the point of being completed. It is not unusual to employ a master tap of an intermediate size. In this case, however, it is obvious the dies will combine, in a modified degree, the defects peculiar to each of the cases before mentioned.

In the Guide Stock this perplexity is entirely obviated, and the dies act with full advantage from the commencement of the operation to the conclusion. They are cut by a master tap double the depth of the thread larger than the screw blank; while their general form and the direction in which they are moved forward, are such as to preserve their cutting power, and steadiness of action undiminished to the full depth of the thread.

The plan of the Guide Stock will be readily understood from the engraving opposite. A, the top plate, fastened by screws a a a; B, a stationary die; CC, moving dies; D, a sliding piece with inclined slides for moving the dies; E, a nut for drawing up the piece D. The interior of the stock is shown by dotted lines through the top plate A.B is a stationary die, C C are moving dies, brought up by a piece D, sliding in a recess in the stock, and bearing with a distinct incline against the back of each die. The piece D is drawn up by a nut E, on the outside of the stock.

The dies having been cut by a fullsized master tap, as before mentioned, the curve made by their outer edges is that of the blank shaft they are intended to screw. Hence, in starting the thread, they bear at all points of the common curve, and the impression made by indentation is the exact copy of the thread of the die. The parts indented serve as a steady guide to the dies, in cutting round the blank shaft. A groove in the stationary die facilitates the operation. Four cutting edges are brought into ac tion, at points of the circumference nearly equidistant, so that by little more than a quarter turn, the thread is completely started round the shaft. The difficulty involved in the operation by the common stock is entirely removed.

After starting the thread, the stationary die serves principally as a guide and abutment for the others. The moving dies are peculiar in their form and direction, both peculiarities depending on the position of the arc in the shank of the

VOL. XXXVII.

The prominent sides of the moving dies are those turned towards each other.

The direction of the common die is necessarily towards the axis of the screw shaft. In the Guide Stock the direction of the moving dies is that of two planes, meeting beyond the centre of the stock, in a line parallel to the axis of the screw shaft, and considerably behind it. This direction is determined by reference to the change which takes place in the relative position of the screw shaft, as the thread is cut deeper. One of the three dies being stationary, there must necessarily be a constant change in the position of the screw shaft in relation to the two others, the effect of which, if not counteracted, would be to deprive the cutting edges of the requisite prominence. By giving them the direction before mentioned, the proper degree of prominence is secured, notwithstanding the change of position. The latter, when combined with the eccentricity of the dies, so far from being any impediment to their action, materially assists it. The newly. formed thread is thereby kept in contact with the dies, for some distance behind their cutting edges, affording them the same kind of support throughout the operation which they have at its commencement, when, as before observed, the curve made by their outer edges is coincident with that of the screw blank. This continued support, which is necessary to steady their action, could not be obtained without a change in the position of the screw shaft. They would otherwise acquire too much clearance as they form the thread deeper, and their cutting edges would be apt to dig.

The steadiness of the Guide Stock, and its easy action in screwing, are equally remarkable. In using it, not one-half the force consumed by the common stock is required. The inner edges of the moving dies (which principally act in cutting out the metal) are filed off to an acute angle. This enables them to cut with extreme ease, and without in any degree distorting the thread, while they take off shavings similar to those cut in a lathe. Their action in cutting is in effect the same as that of a chasing tool, to which they bear an obvious resemblance in form. They may also be sharpened on a grindstone in the same

manner.

A practical difficulty has hitherto at

tended the use of the Screw Stock, arising from the wear of the taps and dies. The tap becomes less in diameter, and consequently taps the hole too small, while the opposite effect takes place wi h the dies, which, being unable to cut a full-sized thread, leave the screw too large. The only mode of counteracting this twofold error, so as to obtain a fit between the screw and nut, is by forcing the dies forward till they have reduced the diameter of the screw a proportionate quantity. From what has been before observed, it is evident that this cannot be done in the case of common dies, without injury to the thread. In using the Guide Stock, on the contrary, it is attended with no disadvantage. Lest the diameter of the screw should be inadvertently reduced more than necessary, figures are stamped on the sides of the set nut E, to indicate when the thread is full.

PROGRESS OF WOOD PAVING.

Sir, In a notice of a work by Colonel Macerone-" Hints to Paviors "-prefaced by some remarks of your own, which appeared in the Monthly Repository of December, 1833, and, if I recollect, continued in January, 1834, I expressed an opinion that the success of wood paving was very doubtful, for several reasons, viz. :

That it would swell in winter, and shrink in summer.

That it would be liable to rot and generate miasma.

That it would be liable to be stolen for fuel, like farmers' fences.

These opinions were grounded on the assumption that deep blocks of wood, of hexagon form, with the grain vertical— the original proposition-were to be used, not merely in leading thoroughfares, but generally, in all districts.

Nearly eight years have elapsed since that time, and wood paving has become general in many leading thoroughfares; and there can be no doubt of its increase, for the following reasons.

1. Houses increase in value in the roughfares of great traffic, inasmuch that, noise and concussion being diminished-almost removed-they are more available as dwellings in technical phraseology, "shopkeepers can let their lodgings."

:

2. The great diminution in wear and tear of horses and vehicles.

3. Greatly increased cleanliness.

Even supposing the expense of maintenance of the pavement to be greater, the great economy induced in other ways is a compensation of manifold amount.

The alleged drawback on the wooden pavement is, the slipping of the horses. This is of little importance, inasmuch as, when the lines are completed, there will be little wear of horse-shoes; and they can be made cross-cut, like a coarse file, and thus produce adhesion. Apart from this, sharp river sand spread upon the surface, from time to time, will materially lessen the evil; and, moreover, horses will learn, like bipeds, to tread securely.

With regard to my expressed opinion as to the swelling of the timber, it has been proved to be an evil in the blocks with vertical grain, in that portion laid near St. Giles's church. It rose occasionally in large swelling patches, and occasionally forced up the side pavements. Summer shrinking never takes place, because the artificial watering prevents it. omitted this element in my calculation.

I

But an alteration has taken place in the mode of laying down. The most approved mode now is, with the grain of the wood at an angle of 45° with the surface of the road. This prevents the swelling of the wood from acting as a la teral wedge, and developes the elasticity usefully, in preventing the effects of concussion. A piece of wood paving may be regarded as a bundle of quills tied up together. Laterally, they have great elasticity; end-ways, none. The bundle of quills may be trodden on without crushing, but the single quill will be crushed under the foot. Upon this principle, wooden pavements, in which the quantity of timber is stinted, will fail, while the larger mass will be successful. It must be obvious, that the most perfect development of the elastic action of the timber will be with the grain parallel to the surface of the road; and the least perfect, at right angles with the surface of the road. But the grain parallel to the road would involve the evil of separation of the fibre, by stripping off in wear; and the most successful general result is, with the grain at an angle of 45° with the surface of the road.

With regard to my opinion as to the liability of the wood pavement to rot and generate miasma, I omitted to take into account, that stagnation is a needful element in generating fungus, or rot. In

the main thoroughfares no stagnation can exist, for they are never quiet; but I have no doubt that, if the dull streets of the West End were lined with deep blocks of vertical grain, and never watered, the result would be, swelling in winter, shrinking in summer, and the generation of nuisance by rotting. On railways, the rails in constant use do not rust-those out of use rust rapidly. And, if laid in by streets and lanes unwatched by the police, the poor would assuredly regard wood pavement as a fuel quarry, as report says the grave-diggers regard coffins in the London burying-grounds.

The rationale of the matter is this. A road, whether bordered by houses or not, requires to be constructed of a certain strength of material proportioned to the traffic, and, if sufficiently strong, would last for ever, but for the destruction of the surface by continual friction, i. e., if no underground agencies, such as water, &c., be at work. To prevent destruction of the surface a tyre is required, which may be renewed as it wears away, precisely like a wheel; and wooden tyre is the best surface for a road, being in sufficient masses not to be crushed by the passing loads.

The practice now obtaining, of intersecting the wood pavement by channels, to give the horses foot-hold, is most mischievous, and will diminish the durability nearly one-half. A system of blows is kept up between the wheels and the wood. It would be far better to make a plain surface, and sand it frequently. Nor must it be forgotten, that the draught on the intersected wood is much increased.

To conclude: I judge that the problem is still to solve between wood pavements and tram ways. The draught on an iron rail is far less than on any wood whatever. A perfectly hard and true circle running on a perfectly hard plane, with a wood understruction, is the point to aim at, to produce the minimum of draught and the maximum of durability; all else is never ending, still beginning, drudging and repair. Wood is a substance furnished by Nature as an expedient for man's intermediate state, and which, when he attains his whole birthright of knowledge will only be used for ornamental purposes. I remain, Sir, yours,

October 15, 1842.

JUNIUS REDIVIVUS.