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.
[Illustration:
FIG. 313_e_.—_A Finished Line entering Galley._
]
[Illustration:
FIG. 313_f_.—_The Melting Pot and Mould Wheel._
]
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.
[Illustration:
FIG. 313_g_.—_The Finished Line._
]
[Illustration:
FIG. 313_h_.—_Lines assembled into a “Form.”_
]
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.
[Illustration:
FIG. 313_i_.—_Matrices dropping into Magazine._
]
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.
[Illustration:
FIG. 314.—_Recording Anemometer._
]
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.
[Illustration:
FIG. 315.—_Registration of Height of Barometer and Thermometer._
]
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.
Modes of making phenomena record the time and duration of their own
occurrence are now much used in all scientific investigations; and in
connection with the electric _chronograph_ or _chronoscope_ which we are
about to describe, few more efficient or elegant methods of
“interrogating nature”—to use Bacon’s phrase—have yet been devised. The
reader who has never seen an instrument of this kind will be the better
able to understand its principle by a simple illustration, which may
very easily be made a practical one by himself if he has a tuning-fork
at hand. Let him fix the tuning-fork firmly into a board in an upright
position, by inserting the part usually held in the hand into a hole in
the board; and then attach to the fork, by means of a little bees’-wax,
a short bristle, which is to project from the extremity of one prong in
a direction perpendicular to the plane in which the prongs vibrate. He
has now only to provide himself with a piece of glass a few inches
square in order to obtain a record of the vibrations of the fork when
sounding. By the help of another piece of board it will be easy to
arrange a guide by which the piece of glass can be made to fall down by
its own weight in a plane parallel to the prongs, and in such a manner
that the free end of the bristle shall just touch its surface during the
whole time of its descent. Now let the surface of the glass be blackened
in the flame of a candle. If the glass be allowed to slide down when the
fork is not vibrating, the end of the bristle, by removing the lampblack
from the surface as the glass falls, would trace out a vertical line.
If, on the other hand, the blackened surface were itself not moved, but
simply brought into contact with the end of the bristle, while the fork
was sounding, there would be marked only a very short horizontal line,
corresponding with the extent of the vibratory movements of the prong.
When the glass is allowed to fall while the prong is in motion, the
combination of the horizontal movements of the bristle, and the vertical
one of the glass, will produce a waved line, which will exhibit
perfectly regular curves if the glass has been moved with uniform
velocity. It is plain that if the time taken by the glass to pass in
front of the bristle were accurately known, the number of movements per
second executed by the prong of the fork could be found. On the other
hand, if the rate of vibration of the fork be known, the time occupied
in the passage of the glass may accurately be read off. If this simple
experiment be understood, the principle of the electric chronograph will
be clear. Substitute for the sliding glass a cylinder covered with white
glazed paper which has been coated with lampblack in the same manner;
suppose the cylinder to revolve at a uniform rate, while a tuning-fork
is similarly writing its vibrations on the surface of the paper, and let
the same mechanism which turns the cylinder, slowly draw the
sounding-fork along a straight slide parallel to the axis of the
cylinder. The waved line will not form a complete circle on the surface
of the cylinder, but will be traced out in a spiral, owing to the
combined motions of the fork and the cylinder. As the number of
movements per second of a vibrating body emitting a given note are
accurately determined and perfectly regular, the waved line on the
cylinder thus furnishes an exact measure of small intervals of time, the
utility of which will presently be seen.
[Illustration:
FIG. 316.—_The Electric Chronograph._
]
Fig. 316 represents the apparatus as actually constructed. A is the
cylinder covered with the blackened paper, and driven by clockwork
contained in the case, B, the rate of movement being regulated by the
conical pendulum at C, so as to be approximately uniform. D is a lever
for starting and stopping the movement. The clockwork also causes the
carriage, E, to slide along the bars, F. This carriage bears three
electro-magnets, and to the armature of each a fine pointed strip of
metal is attached so as just to touch the surface of the cylinder. The
movement of the armatures takes place in a direction parallel to the
axis of the cylinder, and they are acted on by independent currents,
each electro-magnet having its own binding-screws for the attachment of
wires. The armature of one of these is a steel bar, which vibrates in
the manner of the prong of a tuning-fork, at a rate known by the note it
gives out. Sometimes, for delicate experiments, the movements of this
armature are checked and controlled by introducing into its electric
circuit a contact-breaker, formed of a real tuning-fork, the vibrations
of which are maintained by electro-magnets. Another electro-magnet on
the carriage, E, can be connected with the pendulum of a standard clock,
so that seconds may be also marked on the cylinder, as larger units in
the division of the time. In an electric chronograph, which was
exhibited at the International Exhibition of 1862, an ingenious and
excellent mode of making and breaking the electric contacts from the
standard pendulum was adopted. Two short vertical glass tubes, placed
side by side, had each near its lower end a small horizontal branch;
these branches were placed in a line with each other, with their ends in
very close proximity. The larger tubes were filled with mercury which
flowed into the horizontal branches, and the two streams joined in the
narrow space between the ends of the tubes. Although the mercury was
here unsupported by the glass, and surrounded by air only, it did not
run down, for the space was so small that the cohesion of the mercury
itself sufficed to keep the drop hanging between the two open ends of
the tubes. A very thin sheet of mica was carried by an arm of the
pendulum, so placed that at each complete oscillation the mica entered
the space between the two tubes and divided the mercury, and thus all
electrical communication between the two reservoirs was cut off. The
mica remained during one beat of the pendulum in this position; and at
the commencement of the return beat was withdrawn, allowing the divided
columns of mercury to flow together again, and complete the electric
circuit. This admirable make-and-break arrangement acted with the
greatest regularity: the mercury was not spilt, as might have been
expected, there was no friction, and any oxide formed by the spark which
passed when the current was interrupted was removed by the mica. The
pendulum provided with such an arrangement allows the current to pass,
and interrupts it, during alternate seconds, and the result is that the
cylinder is marked with a regularly divided broken line, thus,
¯|_|¯|_|¯|_, the establishment and interruption of the current at the
end of each second being marked with great sharpness and precision.