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They have neither sufficient guide nor die. The two sides have each a different steady abutment, till the operation is on inclination to the arc. As the die moves the point of being completed. It is not forward, one side becomes prominent unusual to employ a master tap of an towards the screw shaft, and its cutting 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 undimin. ished 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 action, 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 edge contines in contact with the thread, position of the arc in the shank of the till it is formed to the full depth required.

VOL. XXXVII.

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The prominent sides of the moving dies tended the use of the Screw Stock, aris. are those turned towards each other. ing from the wear of the taps and dies.

The direction of the common die is The tap becomes less in diameter, and necessarily towards the axis of the screw consequently taps the hole too small

, shaft. In the Guide Stock the direction while the opposite effect takes placewi h of the moving dies is that of two planes, the dies, which, being unable to cut a meeting beyond the centre of the stock, full-sized thread, leave the screw 100 in a line parallel to the axis of the screw large. The only mode of counteracting shaft, and considerably behind it. This this twofold error, so as to obtain a fit direction is determined by reference to between the screw and nut, is by forcing the change which takes place in the re the dies forward till they have reduced lative position of the screw shaft, as the the diameter of the screw a proportionate thread is cut deeper. One of the three quantity: From what has been before dies being stationary, there must neces observed, it is evident that this cannot be sarily be a constant change in the position done in the case of common dies, withof the screw shaft in relation to the two out injury to the thread. In using the others, the effect of which, if not coun Guide Stock, on the contrary, it is atteracted, would be to deprive the cutting tended with no disadvantage. Lest the edges of the requisite prominence. By diameter of the screw should be inadgiving them the direction before men vertently reduced more than necessary, tioned, the proper degree of prominence figures are stamped on the sides of the is secured, notwithstanding the change of set nut E, to indicate when the thread is position. The latter, when combined full. with the eccentricity of the dies, so far from being any impediment to their ac PROGRESS OF WOOD PAVING. tion, materially assists it. The newly. Sir,- In a notice of a work by Colonel formed thread is thereby kept in contact Macerone—“ Hints to Paviors "-prewith the dies, for some distance behind faced by some remarks of your own, their cutting edges, affording them the which appeared in the Monthly Reposi. same kind of support throughout the tory of December, 1833, and, if I recoloperation which they have at its com lect, continued in January, 1834, I ex. mencement, when, as before observed, pressed an opinion that the success of the curve made by their outer edges is wood paving was very doubtful, for sevecoincident with that of the screw blank. ral reasons, viz. : This continued support, which is neces That it would swell in winter, and sary to steady their action, could not be shrink in summer. obtained without a change in the position That it would be liable to rot and geof the screw shaft. They would other nerate miasma. wise acquire too much clearance as they That it would be liable to be stolen for form the thread deeper, and their cutting fuel, like farmers' fences. edges would be apt to dig.

These opinions were grounded on the The steadiness of the Guide Stock, assumption that deep blocks of wood, of and its easy action in screwing, are hexagon form, with the grain verticalequally remarkable. In using it, not the original proposition—were to be used, one-half the force consumed by the com not merely in leading thoroughfares, but mon stock is required. The inner edges generally, in all districts. of the moving dies (which principally Nearly eight years have elapsed since act in cutting out the metal) are filed off that time, and wood paving has become to an acute angle. This enables them to general in many leading thoroughfares; cut with extreme ease, and without in and there can be no doubt of its increase, any degree distorting the thread, while for the following reasons. they take off shavings similar to those 1. Houses increase in value in thocut in a lathe. Their action in cutting roughfares of great traffic, inasmuch that, is in effect the same as that of a chasing noise and concussion being diminished-tool, to which they bear an obvious re almost removed—they are more available semblance in form. They may also be as dwellings : in technical phraseology, sharpened on a grindstone in the same "shopkeepers can let their lodgings. manner.

2. The great diminution in wear and A practical difficulty has hitherto at. tear of horses and vehicles.

3. Greatly increased cleanliness. the main thoroughfares no stagnation can

Even supposing the expense of main- exist, for they are never quiet; but I tenance of the pavement to be greater, have no doubt that, if the dull streets of the great economy induced in other ways the West End were lined with deep blocks is a compensation of manifold amount. of vertical grain, and never watered, the

The alleged drawback on the wooden result would be, swelling in winter, pavement is, the slipping of the horses. shrinking in summer, and the generation This is of little importance, inasmuch as, of nuisance by rotting. On railways, the when the lines are completed, there will rails in constant use do not rust those be little wear of horse-shoes; and they out of use rust rapidly. And, if laid in can be made cross-cut, like a coarse file, by streets and lanes unwatched by the and thus produce adhesion. Apart from police, the poor would assuredly regard this, sharp river sand spread upon the wood pavement as a fuel quarry, as surface, from time to time, will materially report says the grave-diggers regard coflessen the evil; and, moreover, horses fins in the London burying-grounds. will learn, like bipeds, to tread securely. The rationale of the matter is this. A

With regard to my expressed opinion as road, whether bordered by houses or not, to the swelling of the timber, it has been requires to be constructed of a certain proved to be an evil in the blocks with str gth of material proportioned to the vertical grain, in that portion laid near traffic, and, if sufficiently strong, would St. Giles's church. It rose occasionally last for ever, but for the destruction of in large swelling patches, and occasion the surface by continual friction, i. e., if ally forced up the side pavements. Sum no underground agencies, such as water, mer shrinking never takes place, because &c., be at work. To prevent destruction the artificial watering prevents it.

I of the surface a tyre is required, which omitted this element in my calculation. may be renewed as it wears away, pre

But an alteration has taken place in cisely like a wheel; and wooden tyre is the mode of laying down. The most ap. the best surface for a road, being in sufproved mode now is, with the grain of ficient masses not to be crushed by the the wood at an angle of 45° with the sur

passing loads. face of the road. This prevents the The practice now obtaining, of interswelling of the wood from acting as a la secting the wood pavement by channels, teral wedge, and developes the elasticity to give the horses foot-hold, is most misusefully, in preventing the effects of con chievous, and will diminish the durability cussion. A piece of wood paving may be nearly one-half. A system of blows is regarded as a bundle of quills tied up to- kept up between the wheels and the gether. Laterally, they have great elas wood. It would be far better to make a {icity; end-ways, none. The bundle of plain surface, and sand it frequently. quills may be trodden on without crush. Nor must it be forgotten, that the ing, but the single quill will be crushed draught on the intersected wood is much under the foot. Upon this principle, increased. wooden pavements, in which the quantity To conclude : I judge that the proof timber is stinted, will fail, while the blem is still to solve between wood pavelarger mass will be successful. It must ments and tram ways. The draught on be obvious, that the most perfect deve an iron rail is far less than on any wood lopment of the elastic action of the tim whatever.

A perfectly hard and true ber will be with the grain parallel to the circle running on a perfectly hard plane, surface of the road; and the least per. with a wood understruction, is the point fect, at right angles with the surface of to aim at, to produce the minimum of the road. But the grain parallel to the draught and the maximum of durability; road would involve the evil of separation all else is never ending, still beginning, of the fibre, by stripping off in wear ; drudging and repair. Wood is a suband the most successful general result is, stance furnished by Nature as an expewith the grain at an angle of 45° with the dient for man's intermediate state, and surface of the road.

which, when he attains his whole birthWith regard to my opinion as to the right of knowledge will only be used for liability of the wood pavement to rot and ornamental purposes. generate miasma, I omitted to take into

I remain, Sir, yours, account, that stagnation is a needful ele.

Junius REDIVIVUS. ment in generating fungus, or rot. In October 15, 1842.

ON THERMOGRAPHY, OR THE ART OF COPYING ENGRAVINGS, OR ANY PRINTED CHA

RACTERS, FROM PAPER ON METAL PLATES-BY ROBERT HUNT, ESQ., SECRETARY TO THE ROYAL CORNWALL POLYTECHNIC SOCIETY.

[READ AT THE MEETING OF THE SOCIETY, NOVEMBER 8, 1842.] The Journal of the Academy of Sciences we shall still be enabled to see it by the light of Paris, for the 18th of July, 1842, contains which it emits. a communication made by M. Regnault from The human hand will sometimes exhibit M. Moser of Konigsberg, “ Sur la forma the same phenomenon, and many other intion des images Daguerriennes ;''* in which stances might be adduced in proof of the he announces the fact, that “ when two

absorption of light; and, I believe, indeed bodies are sufficiently near, they impress the principle that light is latent in bodies. I their images upon each other." The Jour have only to show that the conclusions of M. nal of the 29th of August contains a second Moser have been formed somewbat hastily, communication from M. Moser, in which being led, no doubt, by the striking similathe results of his researches are summed up rity which exists between the effects produced in twenty-six paragraphs. From these I on the Daguerreotype plates under the inselect the following, which alone are to be influence of light, and by the juxtaposition considered on the present occasion.

of bodies in the dark, to consider them as “ 9. All bodies radiate light even in com the work of the same element. plete darkness.

1. Dr. Draper, in the Philosophical Ma. “ 10. This light does not appear to be gazine for September, 1840, mentions a fact allied to phosphorescence, for there is no dif which has been long known, “ That if a ference perceived whether the bodies have piece of very cold clear glass, or what is bet. been long in the dark, or whether they have ter, a cold polished metallic reflector, has a been just exposed to daylight, or even to di. little object, such as a piece of metal, laid on rect solar light.

it, and the surface be breathed over once, the “ 10. Two bodies constantly impress their object being then carefully removed, as often images on each other, even in complete as you breathe again on the surface, a specdarkness.

tral image of it may be seen, and this sin• 14. However, for the image to be ap gular phenomenon may be exhibited for many preciable it is necessary, because of the di days after the first trial is made.” Several vergence of the rays, that the distance of the similar experiments are mentioned, all of bodies should not be very considerable. them going to show that some mysterious

“ 15. To render the image visible, the molecular change has taken place on the vapour of water, mercury, iodine, &c., may metallic surface, which occasions it to conbe used.

dense vapours unequally. 17. There exists latent light as well as 2. On repeating this simple experiment, latent heat."

I find that it is necessary for the production The announcement at the last meeting of of a good effect, to use dissimilar metals; the British Association of these discoveries, for instance, a piece of gold or platina on a naturally excited a more than ordinary de plate of copper or of silver will make a very gree of interest. A discovery of this kind, decided image, whereas, copper or silver on changing, as it does, the features, not only their respective plates gives but a very faint of the theories of light adopted by philoso one, and bodies which are bad conductors of phers, but also the commonly received opi. heat placed on good conductors, make denions of mankind, was more calculated to cidedly the strongest impressions when thus awaken attention than any thing which has treated. been brought before the public since the 3. I placed upon a well-polished copper publication of Daguerre's beautiful photo plate, a sovereign, a shilling, a large silver graphic process. Having instituted a series medal, and a penny. The plate was gently of experiments, the results of which appear warmed by passing a spirit lamp along its to prove that these phenomena are not pro under surface ; when cold, the plate was duced by latent light, I am desirous of re exposed to the vapour of mercury ; each cording them.

piece had made its impression, but those I would not be understood as denying the made by the gold and the large medal were absorption of light by bodies, of this I think most distinct, not only was the disc marked, we have abundant proof, and it is a matter but the lettering on each was copied. well deserving attention. If we pluck a 4. A bronze medal was supported upon nasturtium when the sun is shining brightly slips of wood, placed on the copper, fth of on the flower, and carry it into a dark room, an inch above the plate. After mercuria

lization, the space the medal covered was • Comptes Rendus, tome xv., No. 3, folio 119. well marked, and for a considerable distance

around the mercury was unequally deposited, vapour of iodine used instead of that of mer. giving a shaded border to the image ; the cury. The impressions of the glasses apspaces touched by the slips of wood were peared in the same order as before, but also thickly covered with the vapour.

a very beautiful image of the mica was deve5. The above coins and medals were all loped, and the paper well marked out, show. placed on the plate, and it was made too hot ing some relation to exist between the subto be handled, and allowed to cool without stances used, and the vapours applied. their being removed ; impressions were made 12. Placed the glasses used above (9, &c.), on the plate in the following order of in with a piece of well-smoked glass for half an tensity,-gold, silver, bronze, copper. The hour, one-twelfth of an inch below a polished mass of the metal was found to influence plate of copper.

The vapour of mercury materially the result; a large piece of cop. brought out the image of the smoked glass per making a better image than a small only. piece of silver. When this plate was ex 13. All these glasses were placed on the posed to vapour, the results were as before copper, and slightly warmed; red and smoked (3, 4). On rubbing off the vapour, it was glasses gave, after vaporization, equally disfound that the gold and silver had made per tinct images; the orange the next; the others manent impressions on the copper.

left but faint marks of their forms. Polishing 6. The above being repeated with a still with Tripoli and putty powder would not greater heat, the image of the copper coin remove the images of the smoked and red was, as well as the others, most faithfully glasses. given, but the gold and silver only made 14. An etching, made upon a smoked permanent impressions.

etching ground on glass, the copper and glass 7. A silvered copper plate was now tried being placed in contact. The image of the with a moderate warmth (3). Mercurial glass only could be brought out. vapour brought out good images of the gold 15. A design cut out in paper, was pressed and copper; the silver marked, but not well close to a copper plate by a piece of glass, defined.

and then exposed to a gentle heat; the im8. Having repeated the above experiments pression was brought out by the vapour of many times with the same results, I was de mercury in beautiful distinctness. On ensirous of ascertaining if electricity had any deavouring to rub off the vapour, it was similar effect ; powerful discharges were found, that all those parts which the paper passed through and over the plate and discs, covered, amalgamated with mercury, which and it was subjected to a long continued cur was removed from the rest of the plates ; rent without any effect. The silver had been hence there resulted a perfectly permanent cleaned off from the plate (7), it was now white picture on a polished copper plate. warmed with the coins and medals upon it, 16. The coloured glasses before named and submitted to discharges from a very (9, 12), were placed on a plate of copper, large Leyden jar; on exposing it to mercurial with a thick piece of charcoal, a copper coin, vapour, the impressions were very prettily the mica and the paper, and exposed to ferbrought out, and strange to say, spectral vent sunshine. Mercurial vapour brought images of those which had been received on up the images in the following order, smoked the plate when it was silvered (7). Thus glass, crown glass, red glass, mica, beautiproving that the influence, whatever it may fully delineated, orange glass, paper, charbe, was exerted to some depth in the metal. coal, the coin, blue glass ; thus distinctly

9. I placed upon a plate of copper, blue, proving, that the only rays which had any ined, and orange coloured glasses, pieces of fluence on the metal, were the calorific rays. crown and flint glass, mica, and a square of This experiment was repeated on different tracing paper. These were allowed to re metals, and with various materials, the plate main in contact half an hour. The space being exposed to steam, mercury, and iodine; occupied by the red glass was well marked, I invariably found that those bodies which that covered by the orange, was less distinct, absorbed or permitted the permeation of but the blue glass left no impression; the the most heat gave the best images. The shapes of the flint and crown glass were well blue and violet rays could not be detected made out, and a remarkably strong impres to leave any evidence of action, and as specsion where the crown glass rested on the tra imprinted on photographic papers by tracing paper, but the mica had not made light, which had permeated these glasses, any impression.

gave evidence of the large quantity of the 10. The last experiment repeated. After invisible rays which passed them freely, we the exposure to mercurial vapour, heat was may also consider those as entirely without again applied to dissipate it; the impression the power of effecting any change on compact still remained.

simple bodies. 11. The experiment repeated, but the 17. In a paper which I published in the

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