LIST OF ELEMENTARY BODIES, WITH THEIR ATOMIC WEIGHTS AND SYMBOLS. In this table the elementary substances whose | the innumerable facts of chemistry, and inscribes names are printed in Italics, have not yet been examined with sufficient care to determine their atomic weights. In the preceding details the combining ratio is stated as always consisting of 1, 2, 3, 4, &c. to 1. In some works on Chemistry we find ratios which appear to contradict this law. Thus the sesquioxide of iron is said to consist of 1 atom of iron, with 1 atom of oxygen; but as half atoms involve a contradiction of terms, it is usual to get over the difficulty by doubling the numbers, so as to make 1 atom of sesquioxide of iron to consist of 2 atoms iron, and 3 of oxygen. Another supposed difficulty in the way of the atomic theory has been in such combinations as sulphuric acid and water, alcohol and water, in which the existence of determinate ratios is indistinct, for these substances appear to combine in all proportions. Such too is the case with the alloys of metals. But it generally happens that where bodies appear to combine in all proportions the affinity is weak; the compound is really not a new substance possessing properties peculiar to itself, and which distinguish it from every other substance in nature; but the compound possesses most of the characters of a mixture; its properties form a mean between those of its constituents, in which the distinctive properties of each constituent can be recognised with greater or less distinctness. them in a sort of short-hand, which is as remarkable for its simplicity as for the truth of its indications. AUGER. AWL. These are instruments for boring wood, of which there are a great number of varieties. The brad-awl is the simplest. It consists of a cylindrical wire with a chisel edge, Fig. 78. It is sometimes sharpened with three facets as a triangular prism. The awl used by wire-workers, such as birdcage makers, &c. Fig. 79, is square and sharp on all Fig. 78. Fig. 79. Fig. 80. Fig. 81. Fig. 82. Fig. 83. its edges, and tapers off very gradually until near the point, where the sides meet rather more abruptly. Tools of this kind displace rather than remove the material which they penetrate. Most of the boring instruments used in carpentry are fluted, in order to give room for the shavings. After all, the doctrine of definite proportions may The shell-bit, Fig. 80, also called the gouge-bit and only be a mere expression of facts essentially different quill-bit, is sharpened at one end like a gouge, and from the real atomic constitution of bodies. Never- when revolving it shears the fibres of the wood round theless, it is a true theory, inasmuch as it generalizes the margin of the hole, and removes the wood almost as a solid core. Very small tools of this kind are used for boring holes in some kinds of brushes. The spoon-bit, Fig. 81, is generally bent up at one end, so as to make a taper point. It acts something like a pointed drill, but has a keen edge suitable for wood. The cooper's dowel-bit, and the table-bit for making holes for the wooden joints of tables, are of this kind. When the end is bent into a semicircular form, it is called a duck nose-bit from its resemblance, and a brush-bit from the use to which it is applied. The nose-bit, slit-nose-bit, and auger-bit, Fig. 82, is slit up a small distance near the centre, and the larger piece of the end is then bent up nearly at right angles to the shaft, so as to act like a paring chisel, and the corner of the reed near the nose also cuts slightly. On a large size this tool is called the shellauger, and is sometimes made 3 inches in diameter and upwards, with long movable shanks for boring pump-barrels. Before using nose-bits a preparatory hole is made with a brad-awl or centre punch; with augers a preparatory hole is always made with a gouge or centre bit of the same size as the auger. The gimlet, Fig. 83, is also a fluted tool, but it terminates in a sharp worm or screw, beginning as a point and extending to the full diameter of the tool, which is thus drawn by the screw into the wood. The gimlet acts like an auger, by cutting the wood by the angular corner between the worm and the shell. When the shell is full of wood the gimlet is with drawn and emptied. The centre-bit, Fig. 84, consists of three parts, viz. a centre point or pin, which serves Fig. 84. as a guide; a thin shearing point or nicker, which cuts through the fibres like the point of a knife; and a broad chisel edge or cutter, placed obliquely, to pare up the wood within the circle marked out by the point. The cutter should have a little less radius, and less length than the nicker. There are many forms of centre-bits described in Mr. Holtzapffel's excellent work, which ought to be in the hands of every practical and amateur mechanic, whether in wood or metal. Various forms of auger are made with spiral stems, so that the shavings may ascend the hollow worm, Fig. 85. Fig. 86. and thus save the trouble of withdrawing the bit so frequently. The twisted gimlet, Fig. 85, is a tool of this kind. It is made with a conical shaft, round which is filed a half-round groove, one edge of which is thus sharpened, and gradually enlarges the hole after the worm has penetrated, and being smaller than in the common gimlet, there is less risk of splitting. The common screw auger, Fig. 86, is forged as a parallel blade of steel, and twisted while red-hot. The end terminates in a worm, by which the auger is gradually drawn into the work. The same kind of shaft is sometimes made with a plain conical point, with two scoring cutters and two chisel edges, forming a sort of double centre-bit. The various kinds of boring bits are usually set in motion by means of the carpenter's brace, one end of which receives the bit, and the other end, consisting of a swivelled head or shield, is pressed forward horizontally by the chest of the workman. Augers are usually moved by transverse handles. Some augers are made with shanks, and are riveted into the handles like the common gimlet; the most common method is to form the end of the shaft into a ring or eye, through which the transverse handle is tightly drawn. Brad-awls and similar tools requiring only a slight force have straight handles.' Mr. Richardson2 states on the authority of Junius, that the word awl has the same origin with eel, and was so called because it can introduce and insinuate itself like an eel. AUTOMATON, from αὐτὸς and μάομαι, a selfmoving machine, or one so constructed, that by means of internal springs and weights or other well known contrivances, it may move for a considerable time as if endowed with life. According to this definition, clocks and watches are automata; indeed, the term automatic machinery has of late years been applied to the self-acting looms and other machines which are now so extensively used in the manufactures of this country. Many early writers delight in narratives of wonderful toy automata, but as they have not stated the mechanical contrivances by which the results were brought about, it is of no use to repeat them here. As an example of the small degree of reliance which can be placed on these narrations, we may refer to the wooden eagle of John Müller of Nuremberg, commonly called Regiomontanus, which flew forth from the city of Nuremberg aloft in the air, and met the emperor Maximilian as he was approaching the city; having saluted him, the bird returned with him to the city gates. This story is gravely related by such eminent authorities as Kircher, Porta, Gassendi, Lana, and Bishop Wilkins, but unfortunately for the truth of it, they do not agree in their dates. Some say it was in the time of Maximilian, others in the time of his grandson Charles V., who was born 64 years after the death of Müller. The same philosopher is also said to have made an iron fly, which at a feast, flew forth from his hand, and taking a round, returned thither, to the astonishment of the guests. This, if true, was probably some kind of magnetic trick. In approaching more modern times, our information is more precise, and the automata are less marvellous. The best examples are those by Vaucansen, Camus, Kempelen and others, and are described by Sir David Brewster in his entertaining little work on Natural Magic. The Automaton (1) Holtzapffel: "Turning and Mechanical Manipulation, vol. ii. (2) A New Dictionary of the English Language, by Charles Richardson. London, 1839 Chess-player of Kempelen was a clever hoax, and the inventor himself was really ashamed at its success. A full history and description of this machine, if such it may be called, is given by the editor in his "Amusement in Chess," London 1845. A few years ago, the editor saw in a watch-maker's room at Geneva, a small automaton, which he believes was invented by M. Maillardet, a clever mechanical artist of the last century. It consisted of a small nest about 3 inches in diameter. On touching a spring, a bird of beautiful plumage, not larger than a small humming-bird, started up and perched on the edge of the nest, fluttering its wings and opening its bill with the tremulous vibration peculiar to singing birds. It then began to warble a rapid succession of notes similar to the song of the nightingale, and loud enough to be heard over the whole room. It then suddenly darted down into its nest, and the nest closed upon it. The song continued about four minutes, and the exhibitor stated that the bird warbled several different strains. We learn from Dr. Brewster,' that the great variety of notes was not produced by a corresponding number of pipes, for which there was evidently no room, but the artist ingeniously managed to have only one pipe, the vacuity of which is shortened or lengthened by a piston working inside, and thus producing sounds graver or more acute according as the machinery operates upon it. The automaton which has, perhaps, received most attention is the speaking machine. A speaking automaton was constructed by Kempelen, and has received further improvements from professors Willis and Wheatstone. A machine of this kind, constructed by a German, was exhibited a few years ago at the Egyptian Hall in London. We cannot say that it was successful. AXIS, a word used in various senses in different departments of science, in which case it is connected with other terms which give it a special meaning and application. Thus we speak of the axis of inertia, of rotation, of refraction, of polarisation, &c. When used by itself, the term generally refers to the axis of rotation or of symmetry. Thus, when a body has a motion of rotation or revolution, the line round which it rotates or revolves is called the axis. So also a line, on both sides of which the parts of a body are similarly disposed, extending as far in one direction as in the other, and in exactly opposite directions, is called the axis of symmetry. The mechanical properties of the axis of rotation are of great importance. In some cases, when the body revolves, the axis itself is movable and in actual motion, as in the earth, the planets, a common spinning top, &c., but generally in mechanics the axis is immovable, or may be regarded as such, as in wheel work, the moving parts of watches and clocks, turning-lathes, mill-work, hinges, &c. Where the axis, or pivot, or joint is not fixed, it may be considered so in reference to the mechanical effect, as in scissors, shears, pincers, &c. (1 Edinburgh Encyclopædia, vol. iii. 1830. In cases where wheel-work is concerned, the body generally turns continually in the same direction, each of its points describing a complete circle during every revolution of the body round its axis; but in some cases the motion is alternate or reciprocal, as in the pendulums of clocks, the balance-wheels of chronometers, the treadle of a lathe, doors or lids on hinges, scissors, pincers, &c. When the alternation is constant and regular, as in pendulums and balancewheels, it is called oscillation or vibration. When a solid body is movable on a fixed axis, it is susceptible of motion only by rotating on that axis. If it be subjected to the action of instantaneous forces, one or other of the following effects will be produced:-1. The axis may resist the forces and prevent any motion. 2. The axis may modify the effect of the forces, thereby sustaining a corresponding percussion, and the body receiving a motion of rotation. 3. The forces may cause the body to rotate round the axis even were it not fixed, in which case the axis will suffer no percussion. A If instead of instantaneous forces, the body be subject to continuous ones, similar effects will be produced, only instead of percussion we get pressure. But " the impressed forces are not the only causes which affect the axis of a body during the phenomenon of rotation. This species of motion calls into action other forces depending on the inertia of the mass, which produce effects upon the axis, and which play a prominent part in the theory of rotation. While the body revolves on its axis, the component particles of its mass move in circles, the centres of which are placed in the axis. The radius of the circle in which each particle moves, is the line drawn from that particle perpendicular to the axis. particle of matter having a circular motion is attended with a centrifugal force proportionate to the radius of the circle in which it moves and to the square of its angular velocity. When a solid body revolves on its axis, all its parts are whirled round together, each performing a complete revolution in the same time. The angular velocity is consequently the same for all, and the difference of the centrifugal forces of different particles must entirely depend upon their distances from the axis. The tendency of each particle to fly from the axis arising from the centrifugal force is resisted by the cohesion of the parts of the mass, and in general, this tendency is expended in exciting a pressure or strain upon the axis. This pressure or strain is, however, altogether different from that already mentioned, and produced by the forces which give motion to the body. The latter depends entirely upon the quantity and directions of the applied forces in relation to the axis; the former depends on the figure and density of the body and the velocity of its motion." These very complex effects do not readily admit of popular exposition; but the reader who is interested in the subject, will find it treated in a lucid manner in the tenth chapter of Dr. Lardner's Mechanics, in the Cabinet Cyclopædia. AXLE. [See WHEEL CARRIAGES.] BAKING. The process of drying and consolidating | planes of steel or agate, finely polished, and placed a substance by means of heat. [See BREAD, BISCUIT, with the greatest care in the same horizontal plane. POTTERY, PORCELAIN, SUGAR, &c.] Fig. 88. BALANCE. An instrument for ascertaining the weight of substances. It is of extensive use in the common affairs of life, in the arts, and in experimental science. It consists essentially of a lever of the first kind, in which the fulcrum is between the The scale-pans are also suspended on knife-edges a power and the weight to be raised. This lever, called | B: the beam, A B, Fig. 87, has its fulcrum or axis of с g* B motion c in the cen- equal. The two extremities of the beam, called the points of suspension, support the scalepans, one of which is for the weights and the other for the substance to be weighed g is the centre of gravity of the beam, and is situated a little below the fulcrum, for if situated in that point, the beam, instead of always being horizontal when the arms are in equilibrium, would rest indifferently in any position; and if the centre of gravity were above the centre of motion, the least disturbance would cause the beam to upset. The points of suspension should be situated so that a straight line A B joining them is perpendicular to the line of symmetry formed by joining the centre of gravity g with the centre of motion m. The direction of the line mg is indicated by a slender pointed needle or tongue, rising perpendicularly above or below the beam: a graduated scale or are behind it shows the deviation of the tongue from the perpendicular, and renders sensible the slightest motion of the beam. When the needle points to the zero line of the scale, which is also in the vertical of the centre of gravity, the beam must be horizontal. By means of this index we can also ascertain whether equilibrium has been attained, without waiting until the beam has ceased to oscillate; for, if it be really in equilibrium, the needle will describe equal arcs on the graduated scale on each side of the zero point, but, if there be not equilibrium, the needle will move through a larger number of degrees on one side of the zero point than on the other. In a perfect balance, all the parts ought to be symmetrical with the centre of gravity; that is, the parts on either side of this point ought to be exactly equal in every respect. But such perfection cannot be attained in practice; the most skilful workman cannot make the two arms perfectly equal; but he approaches this state of perfection as closely as possible. In order to reduce the friction on the axis, the beam is made as light as is consistent with perfect inflexibility. To diminish the extent of surface in contact with the axis, the beam is supported on two sharp edges of tempered steel, c, Fig. 88, lying in the same straight line, and supported on two G is the centre of gravity of the whole beam. D is the point of coincidence of A B and C G. Equality in the length of the arms can be tested in two or three ways. If the balance with its pans vibrate freely, and rest in a horizontal position, and after changing the pans from one end to another the balance again rests horizontally, the arms are almost sure to be equal. Or by changing the weights from one pan to another, if equilibrium be still retained, the lengths of the arms are equal. The weights are usually of brass; but the smaller ones should be of platinum, which is not liable to oxidation or corrosion; and the weights made of this metal can be cleaned from dirt by a slight wiping, or by momentary exposure to the flame of a spirit-lamp. The minute weights, such as the fractions of a grain, are taken up by means of small brass pincers or forceps, as they are too small to be taken up quickly and safely by the hand. There is also danger of moisture or other extraneous matter being communicated to them by handling. The weights are furnished by the maker in sets, from 500 troy grains down to tenths and hundredths of a grain. These weights are frequently arranged in a geometrical series,—1, 2, 4, 8, 16, &c., grains-the advantage of which is that a smaller number of weights is required than in any other system; but the decimal division is convenient in practice. In this case the weights would be 1, 2, 3, 4, &c., up to 10 grains; 10, 20, 30, up to 100; 100, 200, 300, up to 1,000; 1,000, 2,000, up to 9,000. For the fractions the weights would be .1, .2, .3, &c.; .02, .03, .04, &c. ; .001, .002, .003, &c. In this way the trouble of adding is avoided, for the number of weights in the scale is equal to the digits in the number by which the grains are expressed. Thus a load of 735.4 grains is counted by weights of 700 grains, 30 grains, 5 grains, and 4 tenths of a grain. In some of the modern forms of balance one arm is divided into 10 parts, and a small weight, formed of wire twisted into a fork, and weighing th of a grain, placed upon one of the divisions of the arm, which thus acts as a steelyard, indicates from th to th of a grain. The accuracy of the subdivisions is tested by making up equal quantities from different weights, and comparing them together in the balance, a large weight previously compared with a standard weight of good authority being tried against 8 or 10 smaller, as the 100 grain weight against weights of 40, 30, 10, 8, 5, 4, 2, and 1; and then again from a quantity made up of several to remove some and replace them by others, as, for example, for the 30 grain weight to substitute a 10 and four 5 grain weights. The fractions of the grain should be examined in a similar manner, the weight of the beam; by diminishing the distance between the centres of gravity and motion; by diminishing the distance of the line joining the points of suspension from the centre of motion: the sensibility is also greater when the load is smaller. Accurate weighing is a very difficult and delicate operation, requiring numerous precautions which the reader will find clearly stated, together with a large amount of information in the balance, weighing, &c. in the second section of Faraday's invaluable work on "Chemical Manipulation." In weighing for the purposes of chemical analysis, | by increasing the length of its arms; by diminishing an error amounting to the thousandth of a grain might be of importance. But should the arms of the balance be unequal, a very exact result can still be obtained by the method of double weighing invented by Borda. To weigh a body is to ascertain how many times the weight of this body contains another weight of known value. Place the body, which we will call м, in one scale-pan, and produce equilibrium by placing in the other scale-pan some shot, or dry sand, or other substance in a state of minute division, so that very small portions may be added or sub- | tracted, as occasion requires: by this means the needle can be brought exactly to zero, thereby indicating the horizontality of the beam. Then remove the body M, and substitute for it known weights until the beam is again horizontal. The amount of this weight will express exactly the weight of the body м, because these weights being placed under exactly the same circumstances of equilibrium as the body м produce exactly the same effect. In this way it is not only possible, but easy, to weigh truly with a false balance. The ordinary weights and scales for common purposes do not require particular description, but there are various modifications of the lever of the first kind in common use, which are used as weighing machines. Such is the Roman statera or steelyard, Fig. 89, which consists of a beam of iron resting upon knife edges on a pivot, with one arm longer than the other. If the shorter arm with the scale be sufficiently heavy to balance the longer arm when the instrument is unloaded, the beam will, of course, be horizontal. Fig. 89. The tendency of a balance to return to and oscillate about the position of rest, after being disturbed, is called its stability, which is determined by the position of the centre of gravity below the point of support. Stability is far more easily attained than sensibility, or the tendency of a loaded balance, when poised, to turn when a very small additional weight is placed in either scale. In comparing the stability of one balance with that of another, a small amount of disturbance is given to both, such as one degree, and, if the force with which the first endeavours to recover its position be double or triple that of the second, The substance to be weighed, w, is attached to a the stability of the first is double or triple that of the hook on the shorter arm, and a constant weight, P, is second. The sensibility is ascertained by comparing made to slide upon the longer arm, until equilibrium the angles through which very small equal weights is established. Now, in the lever, the condition of incline the balances. Thus, if a grain weight put equilibrium is that the weight w multiplied into into a scale-pan of each inclines one balance 4 degrees, its distance from the fulcrum, is equal to the power and the other only 2 degrees, the first is twice as or counterpoise P multiplied into its distance from sensible as the second. The sensibility of a balance the fulcrum. Now as the distance of the weight is also ascertained by observing the smallest additional from the fulcrum is constant, and the counterpoise is weight that will turn it, and then comparing this also constant, it is evident that in whatever proporaddition with the whole load. Thus, if a balance tion w is increased or diminished, the distance have a troy pound in each scale-pan, and the horizon-between P and the fulcrum must be increased or tality of the beam varies by a small quantity, only diminished in the same proportion. just perceptible, on the addition of th of a grain, the balance is said to be sensible to the 10th part of its load, with a pound in each scale, or that it will determine the weight of a troy pound within 57506th of the whole. One of the most sensible balances ever constructed was that employed fors and c. The great convenience of the steelyard is verifying the national standard bushel, the weight of which, together with the 80 pounds of water which it should contain, was about 250 lbs. With this weight in each scale, the addition of a single grain occasioned an immediate variation in the index of th of an inch, the radius being 50 inches; so that this balance was sensible to both part of the weight to be determined. In the ordinary steelyard, the centre of gravity is not at the fulcrum; so that when the weight P is removed, the longer arm usually preponderates; hence the graduation of the instrument must be commenced, not from c, but from some point between its requiring only one weight. In a pair of common scales, a load of 10 lbs. must be balanced by a weight of 10 lbs. making together a load of 20 lbs.; but in the steelyard, a weight of 10 lbs. may be balanced with only 1 lb., making together a load of only 11 lbs. In the Danish balance, Fig. 90, the fulcrum r is movable, instead of the counterpoise P, Fig. 89, The sensibility of a balance is usually increased which, in this case, is permanently fixed at one |