Part 79

There is reason to hope that the time is not far distant when all our tedious mechanical methods of reproducing drawings by wood or steel engravings will be superseded by processes which will give us absolute facsimiles of every touch of the artist’s pencil; and when some process, giving all the delicacy and truthfulness of Mr. Woodbury’s prints, will supply us with faithful transcripts of nature for book illustration at a cost not exceeding that of the ordinary methods. So far as relates to one style of drawing, these requirements appear to be nearly realized in the process termed the _graphotype_, which reproduces mechanically, in the form of a metal plate with all the lines in relief, a design which the artist has etched on a flat surface. This is effected in the following manner: Chalk is powdered very finely, and sifted through wire gauze having very narrow meshes. A quantity of this is spread upon a smooth plate of metal, and subjected to an intense pressure by means of an hydraulic press. The particles of the chalk cohere into a mass, having sufficient firmness to admit of its surface being drawn upon in the same manner as a block of boxwood. The drawing is effected with an ink composed of lampblack and glue, a finely-pointed camel’s-hair brush being employed; but the shades must be produced by lines and strokes as in wood engraving. When the ink is quite dry, the surface is rubbed with a fitch brush or with velvet; and by this brushing the particles of chalk not protected by the inked strokes are loosened and carried off. In a short time the chalk between the strokes becomes quite hollowed out; and when a depth of about one-eighth of an inch has been attained, every line remains standing in relief exactly as in an engraved wood block. A strong solution of silicate of potash is then poured upon the chalk, which its chemical action converts into a kind of stone without in any way altering the forms. Although this artificial stone is quite hard, so that impressions may at once be taken from it, yet it is incapable of enduring the wear and tear of the printing-press. Accordingly a mould is taken from it, and this is made, by some of the processes of casting or electrotyping already described, to furnish a metal stereotype plate.

_THE LINOTYPE MACHINE._

Among recent inventions in connection with printing, the _linotype machine_ calls for special mention. In this machine a great number of actions are combined and co-ordinated with the utmost ingenuity, but such mechanism does not lend itself to popular description, and we must confine ourselves to a statement of what it effects, recommending the reader to avail himself of some opportunity of seeing the apparatus at work. It will not then be needful to give details of every one of the very numerous parts, which present in the _ensemble_ a great appearance of complication, the more so that much ingenuity has been exerted to make the machine compact, which is a practical point of great importance. The disposition of parts is not, therefore, that which is calculated to show each movement clearly to the spectator, but that by which the least space is occupied. The machine is driven by belting from a main shaft, turned by a steam-engine, gas-engine, electro-motor, or other regular source of power, and rotated at such a rate that the main pulley of the machine itself (14½ inches in diameter) shall make about 60 revolutions per minute. Fig. 313_a_ shows the general aspect of the machine and seat for the one operator required, but as we are not undertaking a detailed and complete description of the whole mechanism, no letters of reference are given; but the reader will be able, from the following diagrams, to identify the more important parts, and form a general idea of their action and purpose. In this machine great use is made of the contrivances called _cams_, several of which may be observed in the sketch towards the side of the machine on the left, being fixed on and turning with its main shaft. They consist of plates, or open rims of various forms, which move levers, etc., in any required way, and at any required period of the revolution.

The linotype is not a type-setting and type-distributing machine, but one in which the form is stereotyped line by line; hence its name of _linotype_. The mould, or matrix, is made up of a number of brass matrices, each of which consists of a flat plate having on its edge a letter incised. One of these is represented on Fig. 313_b_ wherein _a_ is the hollow letter. At the upper end the plate is cut into a number of notches like the teeth of a saw, only that some of the teeth have their points cut off, leaving steps, as it were, with faces parallel to the longer edges of the matrix. There may be seen one of these at _b_, and on the opposite side of the V-shape, three may be observed. The number and arrangement of the cut-away notches is different for the matrix of each letter (or sign), and special to it. The meaning of this will be seen presently. The diagram Fig. 313_c_ will help us to see how these matrices are assembled by touches of the finger on the required letters as marked on the keyboard at D. The matrices are assorted and stored in separate channels in the “matrix” magazine, A, a portion of its cover being here represented as broken off in order to show the channels. It will readily be understood that, by a system of levers connected with each key, the corresponding matrix is released by means of an escapement (B´), and falls down one of the channels E on to the travelling belt F, which conveys it to composing stick G, in which the matrices successively assemble in the order to constitute a line (Fig. 313_c_), in which observe that the several words are separated by spaces formed by long wedges of steel, the thick ends of which hang down considerably below the line of matrices. These are dropped one by one from a store at I (Fig. 313_c_), when required, by a touch on the key-bar J; two of them are shown in position in the assembling stick G. In Fig. 313_a_ a bell is seen in front of the keyboard, and this is automatically rung by a mechanical device when the line of matrices is approaching in length to that allotted to the work. At this point the operator has to consider whether he can complete the line with another, or with how many syllables of a word, and he touches the keys of the required letters. The assembling stick then contains all the matrices comparatively loosely packed side by side, for the words are as yet separated by only the thin edges of the space wedges. A touch of the operator on a lever brings into play another part of the mechanism by which the composed line is bodily lifted a short way, then moved horizontally, and conveyed to the “mould wheel,” in which there is a slot, adjustable in length and width, and the line is here firmly pressed against the face of the wheel in such a way that the slot coincides with the line of hollow letters on the edges of the matrices, as shown in Fig. 313_b_. This moulding arrangement is not the least ingenious device in this machine, and well deserves attention. Before the moulding takes place, but while the line is in its place, the wedge spaces are pushed up through the matrices by another portion of the mechanism, and thus the line is immediately “justified,” as the printers term it; that is, the wedges rise up, separating the words, more or less, until the line has exactly its assigned length, and the words are, at the same time, separated by equal spaces. A melting-pot behind the mould-wheel contains a quantity of fusible metal, resembling stereotype metal, which is maintained at just the temperature of fluidity by a regulated gas burner. At the right moment a plunger is forced into the fluid mass, causing it to rise through a kind of spout to the level of the slot in the wheel, and be forced through that into the line of letters. The metal instantly solidifies in the mould, the line of matrices is removed on a bar to a new position at R, Fig. 313_c_, and the wheel then makes a quarter of a turn, bringing the mould from the horizontal into a vertical position (Fig. 313_e_). The linotype is subjected to the operation of certain knives (not shown), by which it is pared smoothly to the exact thickness and height required, and finally ejected, as shown in Fig. 313_e_, dropping in its proper order into a receiving galley. The line, as completed, has the shape represented in Fig. 313_g_, and a number of these lines assembled constitute a “form,” answering all the purposes of the ordinary forms consisting of separate type. These last, after having served their purpose, must be “distributed,” that is, each single letter must be returned to the case from which it was taken by the compositor; but the linotype form, after use, is simply returned to the melting-pot for its metal to be recast into new forms. The forms can, of course, remain standing for any length of time at the mere expense of keeping the metal unemployed. One advantage of the linotype is that the printing is all done from new clean-faced forms, instead of the old and dull-faced characters of ordinary type that have been much used, but have to be resorted to under ordinary circumstances.

It may occur to the reader that errors in linotype would be much more difficult of correction than those occurring with the ordinary type composed by hand. If by chance a wrong matrix appears in the line, this can be changed by hand at once; but supposing that the operator overlooks some error in reading the assembled line, which, observe, he reads with the characters arranged as they will appear in the impression, or that he has misread his manuscript, and the line is cast, assembled into a “form” with the rest, and then in the printed proof the error is discovered, how is it to be rectified? Simply by removing the faulty linotype from the form, and casting a new one. This is so quickly and easily done that it has been found by actual test between linotype and ordinary type matter containing the same defects, that the former could be corrected in less than one-third of the time required for the latter.

We left the line of matrices at R (Fig. 313_c_), and we must now indicate the method by which each is automatically returned to its own magazine, an operation for which much ingenious mechanism has been contrived, of which the details cannot be well described in this place. The line having reached R, the space wedges are disengaged from it and removed to their receptacle at I, while the matrices become engaged by their teeth in the grooves of a horizontal bar, and then the bar is grasped by a lever which lifts it up to the distributing arrangement at the top of the machine, where the teeth of the matrices come to the exact level of the grooves of the distributor bar T. The line is then pushed laterally, the sides of the matrices become engaged in the hollows of two parallel screws U, by which, while suspended only by such of their inclined teeth as the corresponding groove of the distributor can support, they are made to slowly travel along from left to right until each reaches a certain point, namely, that at which its sustaining V grooves on the bar are interrupted by cuts which permit it to drop into its own special magazine. A little consideration will show how, by various combinations of the notches on the matrix, and corresponding cuts at the right places in the grooves of the bar, each matrix may be made to move along until it reaches a determinate place, and there dropped. Compare Fig. 313_b_ and Fig. 313_i_. Each matrix thus again deposited in its proper magazine has completed the circuit of the machine, or, at least, has passed from the bottom of its magazine to the assembling stick, hence to the mould, and, by the distributor, finds its way back to the top of its magazine, whence, in its turn, it will descend to perform again the same duty.

It must be understood that, beyond the operator’s touches on the key-board, and that required to send off the assembled line to the moulding apparatus, all the actions are done automatically without the interference of the operator, who, while one line is getting moulded, raised up, and distributed, calmly proceeds with the composition of the following one.

The rate at which the work is produced is very great. One good operator with one machine can, it is said, turn out, hour by hour, matter that would be equivalent to two and a half pages of this book, arranged solid or without break. There are, of course, record performances of exceptional operators who have completed more than twice as much as this in a single hour.

RECORDING INSTRUMENTS.

Sir John Herschel, in enumerating at the close of his inestimable “Discourse on the Study of Natural Philosophy” the causes of the rapid development of the physical sciences in modern times, assigns a prominent place to the improvement of scientific apparatus, especially of those instruments by which exact measurements or observations are made. The accurate and elaborate instruments which serve for the delicate and precise determinations and observations of modern science require for their production a very advanced state of mechanical art, such as is indicated by the perfection of the tools we described in a former article; and these tools are themselves, on the other hand, the outcome of accurate knowledge, and another proof of the interaction between science and practical art. Since precise observations and accurate measurements form the essential bases of every science, its progress will be accelerated by every improvement in its instruments which increases their delicacy and exactness. Indeed, hardly any branch of knowledge becomes entitled to be called a science until it rests upon quantitative data of some kind. Chemistry was nothing but a confused collection of vague notions until the exact determinations of the balance were employed, and the proportions of the substances combining or separating in chemical actions were found to be related by certain simple and very definite laws. In all branches of inquiry there is the same necessity of quantitative comparisons: lengths, angles, surfaces, volumes, masses, durations must be compared with standards of their own kind; motions, forces, pressures, temperatures, lights must be measured. The case of chemistry shows the line along which other sciences are advancing. Physiology has made great strides since instruments of precision have been used in its investigations, and as some of these are of the kind we here propose to treat of, they will be described in the sequel. To recording instruments, meteorology is also largely indebted for the remarkable progress which it is making, and which will soon place this branch of knowledge in a condition to supply the most striking illustration of the difference between a science founded on accurate measurements and a mass of vague observations.

The obvious advantage of a recording instrument (say, for example, such a one as that represented in Fig. 314, which registers the force and direction of the wind) is that the results are obtained without the immediate attention of an observer, and they can be continuously recorded at every instant, day and night; but there is another and yet greater advantage in certain kinds of instruments which write their own records, in the fact that they can be made to register results which would altogether escape direct observation. It is said that a practised astronomical observer will correctly record the time of a phenomenon to nearly the tenth of a second; but there are cases in which we may desire to estimate time to the thousandth part of a second or less. An investigation of M. Foucault has already been named in which a far less interval of time was concerned (page 387); but the recording instruments we have to mention here are of use for enabling us to make certain instantaneous actions mark the time of their occurrence with the greatest precision, and also for enabling us to note the variations in actions which are too rapid to be directly observed in their various phases.

Fig. 315 is a diagram which will serve to explain the method in which the height of the barometer and the thermometer are registered in the ingenious _metereograph_, invented by Professor Hough, of Dudley Observatory. The contrivance has the advantage of performing the operation for both instruments, with a single piece of mechanism and on the same sheet of paper. The diagram is not intended to indicate the actual arrangement of the parts of the apparatus, but merely to explain the principle of its action. Let A represent a cylinder about 6 in. in diameter and 7 in. high, covered with a sheet of paper, ruled with certain lines, some parallel to the axis, and others perpendicular to those. This drum revolves by clockwork, controlled by a pendulum, at a certain regular rate of, say, one turn in seven days. B is a metallic bar or lever, about 2 ft. in length, mounted on an axis or fulcrum at C. At D is a pencil or style projecting from the extremity of the bar opposite the centre of the drum, but not in actual contact with the paper. E and F are platinum wires attached to the lever at about 3 in. distance from the fulcrum, C; E passes into the open tube of a mercurial thermometer, G, and F into the shorter branch of a syphon barometer, H. The clockwork has other offices to perform besides turning the drum, A, on its axis; and one of these is to alternately elevate and depress the lever, B, every half-hour. If the end, F, be depressed, it is plain that the wire will come into contact with the metallic float, which is supported by the mercury and follows its movements. If, therefore, wires from a battery, K, including an electro-magnet, I, in their circuit, be connected with the bar at C, and with the mercury at H, when the wire at F touches the float, the current will pass and the armature of the electro-magnet will be attracted. The movement of the armature is so arranged that it causes a blow to be given to the end of the bar D, so that the pen there marks a dot on the drum, thus indicating its height at the time, and therefore that of the mercury in H. When the lever is depressed at the other end, the wire, E, similarly completes the circuit through the mercury in the thermometer, and the height of the latter can be known from the dot which is similarly impressed on the lower part of the paper. These movements may be made with almost any degree of precision required. The clockwork is also made to raise the hammers which strike the pen against the drum, at the instant the electric current passes.

The instrument, as actually constructed, registers also the height of a wet-bulb thermometer, by another wire requiring a lower depression of the lever to bring it into contact with the mercury in a wet-bulb thermometer. A complete double motion of the lever requires one hour, and in that interval the heights of the barometer and both thermometers are each recorded once. The wet and dry-bulb thermometers are registered within a minute of each other, and half an hour elapses between the barometer and thermometer records.

Another invention of Professor Hough’s is a barometer which marks a continuous pencil-line on a revolving cylinder, by which the variations of the mercury are shown for every instant of the day. Another part of the arrangement is a machine for automatically printing on paper in ordinary characters the height of the mercury to the thousandth part of an inch.

A very simple and trustworthy record of thermometric and barometric heights is obtained by photography at Kew and elsewhere. A sheet of sensitive paper passes horizontally at a uniform speed behind the tube of the instrument, so that the only light it can receive must pass through the glass. A lamp is placed in front, and a portion of the paper is protected from its rays by the mercury, while those which pass through the tube above the mercury make their impression on the paper, and thus record the indications of the instrument.

Fig. 314 represents part of another ingenious meteorological instrument invented by Mr. J. E. H. Gordon, and made by Mr. Apps. It is an electrical anemometer, for indicating and registering the direction and force of the wind. The apparatus consists of an external portion, which is of course fixed on some high and exposed part of the building; and the indicating and registering instrument, which communicates with the former only by insulated wires connected with a galvanic battery, and which may be placed on any convenient table within the house. The registering apparatus in this instrument is very neat and compact, and the reader will no doubt be able to form a sufficiently good idea of its nature from the portion which is visible in the cut, and from the knowledge of similar apparatus he may have derived from the descriptions already given in the article on the electric telegraph.