two nicks in the material, that by the longer blade to the full depth of the tooth, and that by the shorter to half the depth; the longer blade is now placed in the shallow nick, which it deepens to its full extent, while a third nick is made by the shorter blade in this manner the whole of the teeth were gradually marked out, and were afterwards finished by means of files. The next improvement was the employment of circular saws of different diameters, instead of the two-bladed straight saw. : The manner in which combs are cut at present is an apt illustration of the advantage derived to manufactures and the arts by the inventions of ingenious men, directed frequently by accident. About twenty years ago, the principal house in London for the sale of combs had received from abroad some patterns of ornaments, like the spikes and balls of coronets, to be attached to tortoise-shell combs. They gave the order to execute these to an ingenious artist of the name of Ricketts, who contrived a punch, by the successive pressure of which, on a thin piece of warm tortoise-shell, he cut out the pattern piece by piece; on disengaging the pattern from the other part, he observed to himself, "Here are two combs cut out of the material for only one." He improved on this hint, and constructed a machine in which he employed a cutter like a chisel, which, descending upon the shell, cut one side of a tooth at a time, and then, by shifting the bed on which the shell was laid, and moving it forward a short distance, the other of the tooth was cut: the result of this operation may be seen in fig. 2, which represents a piece of shell very little larger than necessary for one comb, but which, by this means, is made to produce two. Fig. 2. When the knowledge of this engine began tr spread abroad, various contrivances were resorted to to guide the direction of the cutter, so as to cause it to descend obliquely and at regular intervals; but this oblique action was next avoided by the employment of two cutters, or chisels, placed at an angle with each other, by means of which a perfect tooth is cut at one blow. The scales of tortoise-shell being much thinner on one edge than the other, were not so well adapted for this invention as horn, the thin edge not being thick enough for the back of the comb: but this can be remedied by soldering another piece of shell upon the thin edge; it is effected in this manner. The two surfaces to be united are nicely rasped and smoothed, placed between two thin boards, and submitted to the action of a screw-press. The press is put for some hours in boiling water and tightened The shell is firmly fixed beneath the cutter A, and the engine acts in the following manner:-B is a strong bar firmly jointed behind to the framework; it is kept steady by the loop c, and is moved downwards by means of the crank in front, carrying along with it its cutters upon the shell. This crank is moved by the handle and winch E; and is so fixed that it brings down the cutter upon the shell at that part of the revolution of the winch, when the wheel with a few teeth which is fitted to its axis, is clear of the teeth of the larger wheel. As soon as the tooth is cut, the crank in its revolution raises the lever and cutter, and the teeth on the small wheel entering those of the larger, move the large wheel a part of a revolution. This large wheel is fixed to a screw which is attached to a sliding table, on which the tortoise-shell is placed; the screw is consequently turned a part of a revolu tion, and the shell and table thrust forward proportionately. The smaller wheel becomes again disengaged from the larger, the crank again brings down the cutter on the shell, and another tooth is cut, and this alternate action takes place until the two combs are cut out. Another piece of shell is supplied, and the movement of the handle of the winch being reversed, the shell and the table move back to their former position, and two more combs are separated. If combs with finer teeth are required, the large wheel is changed for another with more teeth on its circumference, and the cutters are also set at an acuter angle. NEWCASTLE-UPON-TYNE, AND THE GREAT NORTHERN COAL-FIELD. II. GREY-STREET-STATUE OF EARL GREY-THE CENTRAL EXCHANGE-MEAT, POULTRY, AND VEGETABLE MARKETS-ROYAL ARCADE-TYNE BRIDGE. WE come now to the examination of the new buildings erected by Mr. Grainger, a gentleman of whom Newcastle is justly proud. Emerging from a comparatively humble station, he displayed at an early age such extraordinary talent as an architect, that he was at once employed to erect every public building required in the town; and the singular beauty of his structures created a desire for fresh buildings, while his integrity won him the confidence of capitalists able to bear the expense of extensive speculations. It was Grey-street is without a rival in the world as a street built merely for business, and resembles rather a street of palaces than houses. It surpasses Regent-street, London, in the richness and variety of its architecture, and in the harmonious arrangement of its parts, and it has the decided advantage of being all built of solid stone, instead of brick faced with stucco. erected in the short space of three years, though its elaborate workmanship would seem to have required the labour of a century. The buildings form groups, each of which seems to be one great public edifice, worthy to have been raised by some powerful monarch. The central group on the west side, occupied by the Northumberland District-Bank, and the Branch-Bank of England, has all the splendour of a palace. Although they are elaborately finished, there is nothing tawdry or meretricious in these edifices, for the parts harmonize with each other, and all the parts are so exquisitely proportioned, that we feel while looking at each building, "here is nothing to be added and nothing to be taken away, without injury to the striking effect of the whole." At the point of entrance from the north to Grey-street and Grainger-street, a column is erected surmounted by a colossal statue of VOL. XIII. Earl Grey in his parliamentary robes. The statue is fourteen feet high, and is an excellent likeness. The total height of the column is 135 feet; a circular staircase within leads to a balcony at the base of the statue, from whence a fine panoramic view of the surrounding country may be obtained. This column. is so placed as to form the termination of Greystreet, called after the noble earl; and of Graingerstreet, which derives its name from the public-spirited architect. The best view of it, however, is from Eldon-square, so called in honour of Lord Eldon, late Lord Chancellor of England, who was a native of Newcastle. The most striking view of Grey-street is from the top of Dean-street; for though the Grey-column is hid by the windings of the street, the cupolas of the Central Exchange are seen at the termination of the vista, and produce a very striking effect by the gorgeous, bronze plumes sculptured on their summits. The Central Exchange was erected by Mr. Grainger for a Corn-market, and offered to the corporation as a free gift. Externally this splendid building displays a rich Corinthian front, slightly varied by the introduction of the other orders, without, however, weakening the unity of the design. But it is scarcely possible to describe the sensations produced by the interior; it presents a semicircle of 150 feet in diameter, with an additional oblong area of twenty feet wide adjoining the diameter. The principal entrance opens into the semicircle, and is surrounded by twelve massive and lofty pillars of the Ionic order, with fancy embellishments. The light of this gigantic edifice is obtained through rather more than ten thousand square feet of glass in the sides of the roof and the crown of the dome. The roof is constructed on a novel principle, somewhat similar to that used in the finest specimens of ecclesiastical architecture, 414 and has a very striking effect when viewed from The meat, poultry, vegetable, and butter markets, are all under one roof, occupying a space of about two acres, having Grainger-street to the east, Claytonstreet to the west, Nelson-street to the north, and Nun-street to the south. These markets occupy the site of a spot called the Nuns'-field, which once belonged to the nunnery of St. Bartholomew, and joined the grounds of the Franciscans, or Grey-friars. This circumstance did not escape the notice of the local poets who abound in Newcastle, and it was commemorated in a song. We may add that there has been scarcely any change made in Newcastle within the last century, which has not been commemorated in a local ballad. The butcher market consists of four spacious avenues, each 338 feet in length, 20 feet in breadth, and 27 feet in height. The light descends in the eastern avenue from fifty sky-lights, through apertures in the coffer ceiling, with a most pleasing effect; there are also the extraordinary number of 360 glazed sashes to open and shut as the weather may require. These four principal avenues are crossed by four lofty arcades, each twelve feet wide. In the evening the whole is lighted with gas, and has a most brilliant effect. for one evening during the recent visit of the British Association to Newcastle, and the scene which it dis played resembled enchantment rather than the work of human hands. The Royal Arcade ranks next to the markets in beauty and convenience. Its front is 94 feet in length and 75 feet in height; the entrance is adorned with two massive pillars of Doric architecture, and the entablature is surmounted by six Corinthian fluted columns, over which is a richly carved frieze. From the front the arcade extends eastwards, and consists of three stories, the basement Doric, and the upper Corinthian, forming an extensive range of sixteen shops and offices, with cellars and shops below, occupying one entire side of Manor-street. The length of the building is 250 feet, the breadth is 20 feet, and the roof, which is 35 feet in height, contains eight conical lanterns, which amply illuminate the building. In this edifice are the Post Office, the Excise Office, and several other public offices, all of which are very spacious and convenient. Tyne Bridge is an edifice of great strength and some beauty; near it is the Close, where anciently the principal inhabitants were accustomed to reside, before Mr. Grainger erected his "city of palaces" in the Upper Town. Most of these houses are now occupied as stores or manufactories ON THE STETHOSCOPE, OR CHEST- ONE of the most remarkable instances of the appli nation. Almost every kind of motion, whether of a solid, a liquid, or an aëriform body, is calculated to produce a sound, more or less audible to the ear: the blast of air which we blow into a flute, and the rush of wind through the key-hole of a door, are, alike, instances of the production of sound by the motion of air: the mighty crash produced by a cataract, or the rippling noise of a flowing brook, show us that the motion of a liquid is a source of sound: while the great majority of our musical instruments, and of the sounds which meet the ear in every-day life, afford us proof of the effect produced by the vibra tion, the friction, or the progressive movement, of solid bodies. The vegetable market consists of one spacious and splendid hall, 318 feet in length, and 57 in width, within the fronts of the fruit and vegetable shops, being of greater dimensions than the venerable hall of Westminster. The roof, upwards of forty feet in height, is framed of timber-work in the cathedral style; it is supported by thirty cast-iron pillars, from each of which, at the height of twenty-six feet, is suspended a large gas-lamp. The roof over the central space is enclosed by a glazed lantern, extending the whole length of the hall, while the sides are lighted by 104 windows. In the centre of the market are two magnificent fountains, similar to the celebrated fountain in the Borghese Palace at Rome; the basins are each capable of containing three thousand gallons of water, and they throw up a jet of twelve feet in height; the water falls into splendid vases of six feet in diameter, beautifully sculptured with foliage and tracery, over whose circumference the water falls in a graceful shower into the large basins below. This market, which is without a A consideration of these circumstances gradually parallel in the world, was fitted up as a promenade led medical men to the inouirv how far the sounds Now, if we consider the structure of the human frame, we become conscious that there are incessant movements going on in the interior of the body, the cessation of which can only occur when death stops the living machine. The flow of blood to and from the heart, the entrance and exit of air in the process of respiration, the forcible passage of air in the process of speaking or singing, all produce sounds differing in intensity and character according to circumstances. Again; if the bony or fleshy parts of the body be struck, the parts are set into a vibratory state, from which results a dull imperfect sound; and this sound is more or less modified by the nature and contents of the cavities which are encompassed by the bony or fleshy portions. emitted by the human body would afford indication of the existence of disease within the system. The lungs, for instance, are suspended in the cavity of the chest, and both within and without the lungs air exists, which air modifies the sounds produced by the natural or the artificial action of the lungs. Now, if through the influence of disease, the solid substance of the lungs become either smaller or larger in bulk than the natural size, the quantity of air to fill the vacant spaces must be changed, and the resonant or echoing effect of sound against the sides of the cavity of the chest, more or less interfered with. If, therefore, in a state of health, a particular sound be emitted from the chest, and if, during the existence of asthma, a different sound be heard, the physician would take that difference of sound as a symbol of the existence of asthma: and so with any other disease. Acting on these principles, Auenbrugger, a physician of Vienna, suggested, in 1761, the mode of percussion, as a means of determining the healthy or unhealthy state of the system. The chest, and other hollow parts of the body, were struck briskly, but not forcibly, with the ends of the fingers, and the ear was applied so as to listen to the sounds resulting from the blows; and an earnest and unremitting attention to the sounds thus elicited, enabled physicians to discriminate between that character of sounds which indicated a sound state of health, and those which appertained to disease; and still further, between those belonging to one disease, and to a different disease. Before we doubt the probability of detecting difference of sound in this way, we must remember how very similar are the means by which artisans frequently hear the state of their work: a bricklayer, by striking a few smart blows on a wall, can frequently determine the thickness and nature of it, by the sound which results from the blow. A carpenter can, by similar means, determine the position of joists, &c., under a boarded floor. These facts prepare us to admit another, that percussion on the chest has been, and still is, resorted to as a means of detecting the existence of disease in the lungs, heart, and adjacent parts. In some cases the chest itself was struck; in others, a layer of cloth was placed between the fingers and the chest; and M. Piorry, a French physician, suggested the application of a thin solid plate between the fingers and the chest, as being advantageous under some circumstances. But it will be observed, that in all these cases, the sound elicited is an artificial and unnatural one, not resulting from the regular movements in the system, but from a disturbance caused from without. It therefore occurred to physicians, that by placing the ear close to the chest, the natural actions of the system might be heard going forward, and that in a state of disease these sounds might be different from those heard in a state of health. This plan has been pursued with considerable success, as a means of obtaining symptoms which may guide the physician in his mode of treatment. But an improvement of an important kind was made in this mode of operation by M. Laennec, a French physician of great eminence. This gentleman was born in Bretagne, in 1781, and while yet a young man, greatly distinguished himself by his skill in auscultation, that is, hearing the sounds emitted by the chest, &c., during the natural actions. In 1816, he was called to attend a patient who had an affection of the heart, and being unable to obtain the requisite symptoms by the application of his ear, he devised a new mode of proceeding. I happened, (says he,) to recollect a simple and wellknown fact in acoustics, and fancied that it might be turned to some use on the present occasion. The fact I allude to is, the great distinctness with which we hear the scratch of a pin at one end of a piece of wood, on applying our ear at the other. Immediately on this suggestion, I rolled a quire of paper into a cylinder, and applied one end of it to my patient's chest, and the other to my ear, and was not a little surprised and pleased, to find that I could thereby perceive the action of the heart, in a manner much more clear and distinct than I had ever been able to do by the immediate application of the ear." Here at once was opened to M. Laennec a new field of investigation, from which he obtained most fruitful results. From his simple quire of paper he proceeded to other materials which he thought might be better fitted for the object in view. In this inquiry he was led to the adoption of an important principle in the science of acoustics, namely, that sonorous vibrations are communicated from one body to another more perfectly, when the conducting body resembles in density the body which is vibrating; that is, that a column of air is best fitted for conducting vibrations excited in air, but that a solid conductor is more appropriate when the vibratory body is a solid or a liquid. Now, Laennec considered that the sounds emanating from the chest, arise from the motion of air to and from and within the lungs ; whereas, the sounds emitted from the heart are caused by the motions of a liquid; that is, the blood. He therefore conceived that a column of air would be the best conductor when the motions of the lungs were to be investigated, but that a solid cylinder of wood would be a better form when the motions of the heart were to be observed. He procured cylinders and tubes of various kinds, and found that a convenient length for this instrument was about ten or twelve inches, and about an inch and a half in diameter. This he formed of walnut, cedar, and other kinds of wood, in order to determine which is best fitted for the purpose. The movement of the air in and round the lungs during respiration, differs from that occasioned by the voice, inasmuch as the latter is confined principally to two tubes or canals proceeding from the lungs to the throat; whereas, during respiration, the whole cellular substance of the lungs furnishes a series of little canals for the passage of air. Laennec conceived, therefore, that to obtain indications of the existence of disease in the lungs, it would be desirable to use a tube, one end of which was spread out like the mouth of a trumpet, by which the action of a larger space might be tested; but for those parts of the contents of the chest connected with the direct production of voice, he found a hollow cylinder, equal in diameter through its whole length, to be the most favourable form. The instrument thus formed he termed the Stethoscope, from two Greek words signifying a chestexplorer, a name significant of its employment. The three forms of the instrument are conveniently combined in one, by a little judicious arrangement. A cylinder nearly a foot long, and an inch and a half in diameter, is employed as a Stethoscope for the heart a small tube bored through the middle of this cylinder, serves as the Stethoscope for the organs of voice; and by unscrewing part of the length of the cylinder, and fixing on a trumpet-shaped piece, the instrument assumes that form most advantageous for the exploration of the respiratory organs. One of the most difficult parts of Laennec's inquiry, was, to find proper language in which to describe the various sounds which the actions of the body emitted. He published a work expressly balls. The redundant electricity accumulated on the inside of the glass, has a tendency to escape to the outside; but glass being a non-conductor, a commu nication is more readily effected by the pith-balls than it would be if the glass were left to itself. The balls, therefore, attracted by the electricity on the inside of the glass, leap from the table towards it, and having received a charge of positive electricity, are instantly repelled by the glass and attracted by the table, to which they return, and after delivering what they have received, leap again to the glass for a further supply. These alternate movements continue until the force of gravity acting on the balls, and the attractive influence of the glass, are exactly balanced. Whilst the pith-balls are engaged in carrying positive electricity from the inside of the glass, it is necessary that negative electricity should in the same proportion make its escape from the outside; a process which is greatly accelerated by passing the hand over it. Hence it happens that the balls, after having been some time at rest, may in this way be made to resume their movements. relating to auscultation by means of the Stethoscope; | find an explanation of the movements of the pithand when detailing the symptoms which indicated disease, he had to convey a correct idea of the sort of sound belonging to each disease. Some of his comparisons are remarkable: one sound is compared to the rush of wind through a small orifice: another to the flapping of a valve: another to the creaking of the leather of a new saddle: a fourth, to the sound produced by stroking the head of a cat while the animal is purring. There is nothing absurd or trifling in such comparisons, since it is as impossibe to find appropriate and expressive names for all the varieties of sound, as for all the tints of colour: in order, therefore, to convey to others a precise idea of the nature of a sound, it is necessary to adopt such a standard of comparison as is familiar to most persons. In the application of the Stethoscope, the ear is applied closely to one end, whilst the other end is placed against various parts of the chest, according to the spot which it is wished to explore. In some cases a tube of caoutchouc, or Indian rubber, has been employed instead of wood; but the impossibility of rendering the internal surface of such a tube perfectly smooth and cylindrical, detracts from its usefulness; for whenever sounds have to be conveyed through a tube, it is of much importance that the sides of the tube should be free from any protuberances or roughness of surface. ELECTRICITY. ELECTRICAL EXPERIMENTS. THE following, notwithstanding its apparent simplicity, is as good an experiment as we can select for illustrating electrical attraction and repulsion. Having provided a glass vessel of the form represented in the annexed figure, or a large tumbler will do equally well, let it be wiped clean and perfectly dry, and by means of a pointed wire attached to the positive conductor of the electrical machine, the inside of the glass must be charged with electricity. If it then be placed on a table, and made to cover a dozen or two of pith-balls, the latter will immediately begin to leap from the table to the top and sides of the glass, and back again, and this they will continue to do for several minutes. When the motions of the balls have ceased, they will almost always be renewed on passing the hand gently over the outside of the glass. With so great a number of balls as we have mentioned, this experiment is, perhaps, more amusing than instructive; but when only about half a dozen are used, and those of different colours or sizes, if we watch attentively their movements, we shall have no difficulty in understanding the cause. On presenting the inside of the glass vessel to the pointed wire, as just described, its surface becomes coated with positive electricity, and at the same time, and exactly to the same degree of intensity, the outside of the glass will be negatively electrified. The instant the glass is placed on the table, the pith-balls and that part of the surface of the table directly underneath it, are similarly affected. We have before stated as a first principle in this branch of science, that bodies similarly electrified repel, those dissimilarly electrified attract each other. Here, then, we Another experiment, furnishing an example of electrical repulsion, is effected by means of what is called an electrical head of hair; consisting of a block of hard wood, carved and painted to represent a human head, and covered with long hair, the finer the better. A piece of wood, or stout brass wire, projects from the lower part of the head, by which it is fixed to the conductor. On putting the machine in motion, the electricity excited by it escapes at the points of the hair, which separate and stand erect, presenting a most grotesque appearance, and which is occasioned by each hair being similarly electrified. These examples, all tending to illustrate the same principle, may be greatly multiplied; and although the apparatus partakes in some respects of the character of philosophical toys, yet it is not on that account to be despised. Of this class is the electrical bells, which are so arranged that, by the alternate attractions and repulsions of small brass clappers placed outside them, a constant peal is kept up. The arrangement is as follows; (see fig.) a is a brass hook fixed to a piece of wire, the length of which must be determined by the size of the bells, and it may either be straight or curved, but the latter form is the best. bbb are three bells, the outside ones suspended by brass chains, but that in the centre by silk cord, as are also the clappers cc. bell is made to communicate with the table or floor by a piece of chain c. The centre by the hook a, on turning the machine the electricity The bells being attached to the positive conductor endeavours to make its escape down the chains by which the two outside bells are suspended, and which are, of course, positively electrified; that in the centre, by its communication with the earth, being in |