VARIOUS MECHANISMS.
CLOCKS AND WATCHES:--A short history of timepieces--The
construction of timepieces--The driving power--The
escapement--Compensating pendulums--The spring balance--The
cylinder escapement--The lever escapement--Compensated
balance-wheels--Keyless winding mechanism for watches--The hour
hand train. LOCKS:--The Chubb lock--The Yale lock. THE CYCLE:--The
gearing of a cycle--The free wheel--The change-speed gear.
AGRICULTURAL MACHINES:--The threshing-machine--Mowing-machines.
SOME NATURAL PHENOMENA:--Why sun-heat varies in intensity--The
tides--Why high tide varies daily.
CLOCKS AND WATCHES.
A SHORT HISTORY OF TIMEPIECES.
The oldest device for measuring time is the sun-dial. That of Ahaz
mentioned in the Second Book of Kings is the earliest dial of which we
have record. The obelisks of the Egyptians and the curious stone pillars
of the Druidic age also probably served as shadow-casters.
The clepsydra, or water-clock, also of great antiquity, was the first
contrivance for gauging the passage of the hours independently of the
motion of the earth. In its simplest form it was a measure into which
water fell drop by drop, hour levels being marked on the inside.
Subsequently a very simple mechanism was added to drive a pointer--a
float carrying a vertical rack, engaging with a cog on the pointer
spindle; or a string from the float passed over a pulley attached to the
pointer and rotated it as the float rose, after the manner of the wheel
barometer (Fig. 153). In 807 A.D. Charlemagne received from the King of
Persia a water-clock which struck the hours. It is thus described in
Gifford's "History of France":--"The dial was composed of twelve small
doors, which represented the division of the hours. Each door opened at
the hour it was intended to represent, and out of it came a small number
of little balls, which fell one by one, at equal distances of time, on a
brass drum. It might be told by the eye what hour it was by the number
of doors that were open, and by the ear by the number of balls that
fell. When it was twelve o'clock twelve horsemen in miniature issued
forth at the same time and shut all the doors."
Sand-glasses were introduced about 330 A.D. Except for special
purposes, such as timing sermons and boiling eggs, they have not been of
any practical value.
The clepsydra naturally suggested to the mechanical mind the idea of
driving a mechanism for registering time by the force of gravity acting
on some body other than water. The invention of the _weight-driven
clock_ is attributed, like a good many other things, to Archimedes, the
famous Sicilian mathematician of the third century B.C.; but no record
exists of any actual clock composed of wheels operated by a weight prior
to 1120 A.D. So we may take that year as opening the era of the clock as
we know it.
About 1500 Peter Hele of Nuremberg invented the _mainspring_ as a
substitute for the weight, and the _watch_ appeared soon afterwards
(1525 A.D.). The pendulum was first adopted for controlling the motion
of the wheels by Christian Huygens, a distinguished Dutch mechanician,
in 1659.
To Thomas Tompion, "the father of English watchmaking," is ascribed the
honour of first fitting a _hairspring_ to the escapement of a watch, in
or about the year 1660. He also introduced the _cylinder escapement_ now
so commonly used in cheap watches. Though many improvements have been
made since his time, Tompion manufactured clocks and watches which were
excellent timekeepers, and as a reward for the benefits conferred on his
fellows during his lifetime, he was, after death, granted the
exceptional honour of a resting-place in Westminster Abbey.
THE CONSTRUCTION OF TIMEPIECES.
A clock or watch contains three main elements:--(1) The source of power,
which may be a weight or a spring; (2) the train of wheels operated by
the driving force; (3) the agent for controlling the movements of the
train--this in large clocks is usually a pendulum, in small clocks and
watches a hairspring balance. To these may be added, in the case of
clocks, the apparatus for striking the hour.
THE DRIVING POWER.
_Weights_ are used only in large clocks, such as one finds in halls,
towers, and observatories. The great advantage of employing weights is
that a constant driving power is exerted. _Springs_ occupy much less
room than weights, and are indispensable for portable timepieces. The
employment of them caused trouble to early experimenters on account of
the decrease in power which necessarily accompanies the uncoiling of a
wound-up spring. Jacob Zech of Prague overcame the difficulty in 1525 by
the invention of the _fusee_, a kind of conical pulley interposed
between the barrel, or circular drum containing the mainspring, and the
train of wheels which the spring has to drive. The principle of the
"drum and fusee" action will be understood from Fig. 201. The mainspring
is a long steel ribbon fixed at one end to an arbor (the watchmaker's
name for a spindle or axle), round which it is tightly wound. The arbor
and spring are inserted in the barrel. The arbor is prevented from
turning by a ratchet, B, and click, and therefore the spring in its
effort to uncoil causes the barrel to rotate.
[Illustration: FIG. 201.]
A string of catgut (or a very fine chain) is connected at one end to
the circumference of the drum, and wound round it, the other end being
fixed to the larger end of the fusee, which is attached to the
driving-wheel of the watch or clock by the intervention of a ratchet and
click (not shown). To wind the spring the fusee is turned backward by
means of a key applied to the square end A of the fusee arbor, and this
draws the string from off the drum on to the fusee. The force of the
spring causes the fusee to rotate by pulling the string off it, coil by
coil, and so drives the train of wheels. But while the mainspring, when
fully wound, turns the fusee by uncoiling the string from the smallest
part of the fusee, it gets the advantage of the larger radius as its
energy becomes lessened.
The fusee is still used for marine chronometers, for some clocks that
have a mainspring and pendulum, and occasionally for watches. In the
latter it has been rendered unnecessary by the introduction of the
_going-barrel_ by Swiss watchmakers, who formed teeth on the edge of the
mainspring barrel to drive the train of wheels. This kind of drum is
called "going" because it drives the watch during the operation of
winding, which is performed by rotating the drum arbor to which the
inner end of the spring is attached. A ratchet prevents the arbor from
being turned backwards by the spring. The adoption of the going-barrel
has been made satisfactory by the improvements in the various escapement
actions.
THE ESCAPEMENT.
[Illustration: FIG. 202.]
The spring or weight transmits its power through a train of cogs to the
_escapement_, or device for regulating the rate at which the wheels are
to revolve. In clocks a _pendulum_ is generally used as the controlling
agent. Galileo, when a student at Pisa, noticed that certain hanging
lamps in the cathedral there swung on their cords at an equal rate; and
on investigation he discovered the principle that the shorter a pendulum
is the more quickly will it swing to and fro. As has already been
observed, Huygens first applied the principle to the governing of
clocks. In Fig. 202 we have a simple representation of the "dead-beat"
escapement commonly used in clocks. The escape-wheel is mounted on the
shaft of the last cog of the driving train, the pallet on a spindle
from which depends a split arm embracing the rod and the pendulum. We
must be careful to note that the pendulum _controls_ motion only; it
does not cause movement.
The escape-wheel revolves in a clockwise direction. The two pallets _a_
and _b_ are so designed that only one can rest on the teeth at one time.
In the sketch the sloping end of _b_ has just been forced upwards by the
pressure of a tooth. This swings the pallet and the pendulum. The
momentum of the latter causes _a_ to descend, and at the instant when
_b_ clears its tooth _a_ catches and holds another. The left-hand side
of _a_, called the _locking-face_, is part of a circle, so that the
escape-wheel is held motionless as long as it touches _a_: hence the
term, "dead beat"--that is, brought to a dead stop. As the pendulum
swings back, to the left, under the influence of gravity, _a_ is raised
and frees the tooth. The wheel jerks round, and another tooth is caught
by the locking-face of _b_. Again the pendulum swings to the right, and
the sloping end of _b_ is pushed up once more, giving the pendulum fresh
impetus. This process repeats itself as long as the driving power
lasts--for weeks, months, or years, as the case may be, and the
mechanism continues to be in good working order.
COMPENSATING PENDULUMS.
Metal expands when heated; therefore a steel pendulum which is of the
exact length to govern a clock correctly at a temperature of 60° would
become too long at 80°, and slow the clock, and too short at 40°, and
cause it to gain. In common clocks the pendulum rod is often made of
wood, which maintains an almost constant length at all ordinary
temperatures. But for very accurate clocks something more efficient is
required. Graham, the partner of Thomas Tompion, took advantage of the
fact that different kinds of metal have different ratios of expansion to
produce a _self-compensating_ pendulum on the principle illustrated by
Fig. 203. He used steel for the rod, and formed the _bob_, or weighted
end, of a glass jar containing mercury held in a stirrup; the mercury
being of such a height that, as the pendulum rod lengthened with a rise
of temperature, the mercury expanded _upwards_ sufficiently to keep the
distance between the point of suspension and the centre of gravity of
the bob always the same. With a fall of temperature the rod shortened,
while the mercury sank in the jar. This device has not been improved
upon, and is still used in observatories and other places where
timekeepers of extreme precision are required. The milled nut S in Fig.
203 is fitted at the end of the pendulum rod to permit the exact
adjustment of the pendulum's length.
For watches, chronometers, and small clocks
THE SPRING BALANCE
takes the place of the pendulum. We still have an escape-wheel with
teeth of a suitable shape to give impulses to the controlling agent.
There are two forms of spring escapement, but as both employ a
hairspring and balance-wheel we will glance at these before going
further.
[Illustration: FIG. 203.]
The _hairspring_ is made of very fine steel ribbon, tempered to extreme
elasticity, and shaped to a spiral. The inner end is attached to the
arbor of the _balance-wheel_, the outer end to a stud projecting from
the plate of the watch. When the balance-wheel, impelled by the
escapement, rotates, it winds up the spring. The energy thus stored
helps the wheel to revolve the other way during the locking of a tooth
of the escape-wheel. The time occupied by the winding and the unwinding
depends upon the length of the spring. The strength of the impulse makes
no difference. A strong impulse causes the spring to coil itself up more
than a weak impulse would; but inasmuch as more energy is stored the
process of unwinding is hastened. To put the matter very simply--a
strong impulse moves the balance-wheel further, but rotates it quickly;
a weak impulse moves it a shorter distance, but rotates it slowly. In
fact, the principle of the pendulum is also that of the hairspring; and
the duration of a vibration depends on the length of the rod in the one
case, and of the spring in the other.
Motion is transmitted to the balance by one of two methods. Either (1)
directly, by a cylinder escapement; or (2) indirectly, through a lever.
[Illustration: FIG. 204.--"Cylinder" watch escapement.]
THE CYLINDER ESCAPEMENT
is seen in Fig. 204. The escape-wheel has sharp teeth set on stalks.
(One tooth is removed to show the stalk.) The balance-wheel is mounted
on a small steel cylinder, with part of the circumference cut away at
the level of the teeth, so that if seen from above it would appear like
_a_ in our illustration. A tooth is just beginning to shove its point
under the nearer edge of the opening. As it is forced forwards, _b_ is
revolved in a clockwise direction, winding up the hairspring. When the
tooth has passed the nearer edge it flies forward, striking the inside
of the further wall of the cylinder, which holds it while the spring
uncoils. The tooth now pushes its way past the other edge, accelerating
the unwinding, and, as it escapes, the next tooth jumps forward and is
arrested by the outside of the cylinder. The balance now reverses its
motion, is helped by the tooth, is wound up, locks the tooth, and so on.
THE LEVER ESCAPEMENT
is somewhat more complicated. The escape-wheel teeth are locked and
unlocked by the pallets P P^1 projecting from a lever which moves on a
pivot (Fig. 205). The end of the lever is forked, and has a square notch
in it. On the arbor of the balance-wheel is a roller, or plate, R, which
carries a small pin, I. Two pins, B B, projecting from the plate of the
watch prevent the lever moving too far. We must further notice the
little pin C on the lever, and a notch in the edge of the roller.
[Illustration: FIG. 205.--"Lever" watch escapement.]
In the illustration a tooth has just passed under the "impulse face" _b_
of P^1. The lever has been moved upwards at the right end; and its
forked end has given an impulse to R, and through it to the
balance-wheel. The spring winds up. The pin C prevents the lever
dropping, because it no longer has the notch opposite to it, but presses
on the circumference of R. As the spring unwinds it strikes the lever at
the moment when the notch and C are opposite. The lever is knocked
downwards, and the tooth, which had been arrested by the locking-face
_a_ of pallet P, now presses on the impulse face _b_, forcing the left
end of the lever up. The impulse pin I receives a blow, assisting the
unwinding of the spring, and C again locks the lever. The same thing is
repeated in alternate directions over and over again.
COMPENSATING BALANCE-WHEELS.
The watchmaker has had to overcome the same difficulty as the clockmaker
with regard to the expansion of the metal in the controlling agent. When
a metal wheel is heated its spokes lengthen, and the rim recedes from
the centre. Now, let us suppose that we have two rods of equal weight,
one three feet long, the other six feet long. To an end of each we
fasten a 2-lb. weight. We shall find it much easier to wave the shorter
rod backwards and forwards quickly than the other. Why? Because the
weight of the longer rod has more leverage over the hand than has that
of the shorter rod. Similarly, if, while the mass of the rim of a wheel
remains constant, the length of the spokes varies, the effort needed to
rotate the wheel to and fro at a constant rate must vary also. Graham
got over the difficulty with a rod by means of the compensating
pendulum. Thomas Earnshaw mastered it in wheels by means of the
_compensating balance_, using the same principle--namely, the unequal
expansion of different metals. Any one who owns a compensated watch will
see, on stopping the tiny fly-wheel, that it has two spokes (Fig. 206),
each carrying an almost complete semicircle of rim attached to it. A
close examination shows that the rim is compounded of an outer strip of
brass welded to an inner lining of steel. The brass element expands more
with heat and contracts more with cold than steel; so that when the
spokes become elongated by a rise of temperature, the pieces bend
inwards at their free ends (Fig. 207); if the temperature falls, the
spokes are shortened, and the rim pieces bend outwards (Fig. 208).[39]
This ingenious contrivance keeps the leverage of the rim constant
within very fine limits. The screws S S are inserted in the rim to
balance it correctly, and very fine adjustment is made by means of the
four tiny weights W W. In ships' chronometers,[40] the rim pieces are
_sub_-compensated towards their free ends to counteract slight errors in
the primary compensation. So delicate is the compensation that a daily
loss or gain of only half a second is often the limit of error.
[Illustration: FIG. 206. FIG. 207. FIG. 208. A "compensating" watch
balance, at normal, super-normal, and sub-normal temperatures.]
KEYLESS WINDING MECHANISM FOR WATCHES.
The inconvenience attaching to a key-wound watch caused the Swiss
manufacturers to put on the market, in 1851, watches which dispensed
with a separate key. Those of our readers who carry keyless watches will
be interested to learn how the winding and setting of the hands is
effected by the little serrated knob enclosed inside the pendant ring.
There are two forms of "going-barrel" keyless mechanism--(1) The rocking
bar; (2) the shifting sleeve. The _rocking bar_ device is shown in Figs.
209, 210. The milled head M turns a cog, G, which is always in gear with
a cog, F. This cog gears with two others, A and B, mounted at each end
of the rocker R, which moves on pivot S. A spring, S P, attached to the
watch plate presses against a small stud on the rocking bar, and keeps A
normally in gear with C, mounted on the arbor of the mainspring.
[Illustration: FIG. 209.--The winding mechanism of a keyless watch.]
To wind the watch, M is turned so as to give F an anti-clockwise motion.
The teeth of F now press A downwards and keep it in gear with C while
the winding is done. A spring click (marked solid black) prevents the
spring uncoiling (Fig. 209). If F is turned in a clockwise direction it
lifts A and prevents it biting the teeth of C, and no strain is thrown
on C.
To set the hands, the little push-piece P is pressed inwards by the
thumb (Fig. 210) so as to depress the right-hand end of R and bring B
into gear with D, which in turn moves E, mounted on the end of the
minute-hand shaft. The hands can now be moved in either direction by
turning M. On releasing the push-piece the winding-wheels engage again.
The _shifting sleeve_ mechanism has a bevel pinion in the place of G
(Fig. 209) gearing with the mainspring cog. The shaft of the knob M is
round where it passes through the bevel and can turn freely inside it,
but is square below. On the square part is mounted a little sliding
clutch with teeth on the top corresponding with the other teeth on the
under side of the bevel-wheel, and teeth similar to those of G (Fig.
209) at the end. The clutch has a groove cut in the circumference, and
in this lies the end of a spring lever which can be depressed by the
push-piece. The mechanism much resembles on a small scale the motor car
changing gear (Fig. 49). Normally, the clutch is pushed up the square
part of the knob shaft by the spring so as to engage with the bevel and
the winding-wheels. On depressing the clutch by means of the push-piece
it gears with the minute-hand pinion, and lets go of the bevel.
[Illustration: FIG. 210.--The hand-setting mechanism in action.]
In one form of this mechanism the push-piece is dispensed with, and the
minute-wheel pinion is engaged by pulling the knob upwards.
THE HOUR-HAND TRAIN.
[Illustration: FIG. 211.--The hour-hand train of a clock.]
The teeth of the mainspring drum gear with a cog on the minute-hand
shaft, which also carries one of the cogs of the escapement train. The
shaft is permitted by the escapement to revolve once an hour. Fig. 211
shows diagrammatically how this is managed. The hour-hand shaft A (solid
black) can be moved round inside the cog B, driven by the mainspring
drum. It carries a cog, C. This gears with a cog, D, having three times
as many teeth. The cog E, united to D, drives cog F, having four times
as many teeth as E. To F is attached the collar G of the hour-hand. F
and G revolve outside the minute-hand shaft. On turning A, C turns D and
E, E turns F and the hour-hand, which revolves 1/3 of 1/4 = 1/12 as fast
as A.[41]
* * * * *
LOCKS.
On these unfortunately necessary mechanisms a great deal of ingenuity
has been expended. With the advance of luxury and the increased worship
of wealth, it becomes more and more necessary to guard one's belongings
against the less scrupulous members of society.
[Illustration: FIG. 212.]
The simplest form of lock, such as is found in desks and very cheap
articles, works on the principle shown in Fig. 212. The bolt is split at
the rear, and the upper part bent upwards to form a spring. The under
edge has two notches cut in it, separated by a curved excrescence. The
key merely presses the bolt upwards against the spring, until the notch,
engaging with the frame, moves it backwards or forwards until the spring
drives the tail down into the other notch. This primitive device
affords, of course, very little security. An advance is seen in the
TUMBLER LOCK.
[Illustration: FIG. 213.]
The bolt now can move only in a horizontal direction. It has an opening
cut in it with two notches (Figs. 213, 214). Behind the bolt lies the
_tumbler_ T (indicated by the dotted line), pivoted at the angle on a
pin. From the face of the tumbler a stud, S, projects through the hole
in the bolt. This stud is forced into one or other of the notches by the
spring, S^1, which presses on the tail of the tumbler.
[Illustration: FIG. 214.]
In Fig. 213 the key is about to actuate the locking mechanism. The next
diagram (Fig. 214) shows how the key, as it enters the notch on the
lower side of the bolt to move it along, also raises the tumbler stud
clear of the projection between the two notches. By the time that the
bolt has been fully "shot," the key leaves the under notch and allows
the tumbler stud to fall into the rear locking-notch.
A lock of this type also can be picked very easily, as the picker has
merely to lift the tumbler and move the bolt along. Barron's lock,
patented in 1778, had two tumblers and two studs; and the opening in the
bolt had notches at the top as well as at the bottom (Fig. 215). This
made it necessary for both tumblers to be raised simultaneously to
exactly the right height. If either was not lifted sufficiently, a stud
could not clear its bottom notch; if either rose too far, it engaged an
upper notch. The chances therefore were greatly against a wrong key
turning the lock.
[Illustration: FIG. 215.--The bolt of a Barron lock.]
THE CHUBB LOCK
is an amplification of this principle. It usually has several tumblers
of the shape shown in Fig. 216. The lock stud in these locks projects
from the bolt itself, and the openings, or "gates," through which the
stud must pass as the lock moves, are cut in the tumblers. It will be
noticed that the forward notch of the tumbler has square serrations in
the edges. These engage with similar serrations in the bolt stud and
make it impossible to raise the tumbler if the bolt begins to move too
soon when a wrong key is inserted.
[Illustration: FIG. 216.--Tumbler of Chubb lock.]
Fig. 217 is a Chubb key with eight steps. That nearest the head (8)
operates a circular revolving curtain, which prevents the introduction
of picking tools when a key is inserted and partly turned, as the key
slot in the curtain is no longer opposite that in the lock. Step 1 moves
the bolt.
[Illustration: FIG. 217.--A Chubb key.]
In order to shoot the bolt the height of the key steps must be so
proportioned to the depth of their tumblers that all the gates in the
tumblers are simultaneously raised to the right level for the stud to
pass through them, as in Fig. 218. Here you will observe that the
tumbler D on the extreme right (lifted by step 2 of the key) has a stud,
D S, projecting from it over the other tumblers. This is called the
_detector tumbler_. If a false key or picking tool is inserted it is
certain to raise one of the tumblers too far. The detector is then
over-lifted by the stud D S, and a spring catch falls into a notch at
the rear. It is now impossible to pick the lock, as the detector can be
released only by the right key shooting the bolt a little further in the
locking direction, when a projection on the rear of the bolt lifts the
catch and allows the tumbler to fall. The detector also shows that the
lock has been tampered with, since even the right key cannot move the
bolt until the overlocking has been performed.
[Illustration: FIG. 218.--A Chubb key raising all the tumblers to the
correct height.]
Each tumbler step of a large Chubb key can be given one of thirty
different heights; the bolt step one of twenty. By merely transposing
the order of the steps in a six-step key it is possible to get 720
different combinations. By diminishing or increasing the heights the
possible combinations may be raised to the enormous total of 7,776,000!
[Illustration: FIG. 219.--Section of a Yale lock.]
THE YALE LOCK,
which comes from America, works on a quite different system. Its most
noticeable feature is that it permits the use of a very small key,
though the number of combinations possible is still enormous (several
millions). In our illustrations (Figs. 219, 220, 221) we show the
mechanism controlling the turning of the key. The keyhole is a narrow
twisted slot in the face of a cylinder, G (Fig. 219), which revolves
inside a larger fixed cylinder, F. As the key is pushed in, the notches
in its upper edge raise up the pins A^1, B^1, C^1, D^1, E^1,
until their tops exactly reach the surface of G, which can now be
revolved by the key in Fig. 220, and work the bolt through the medium of
the arm H. (The bolt itself is not shown.) If a wrong key is inserted,
either some of the lower pins will project upwards into the fixed
cylinder F (see Fig. 221), or some of the pins in F will sink into G. It
is then impossible to turn the key.
[Illustration: FIG. 220.--Yale key turning.]
There are other well-known locks, such as those invented by Bramah and
Hobbs. But as these do not lend themselves readily to illustration no
detailed account can be given. We might, however, notice the _time_
lock, which is set to a certain hour, and can be opened by the right key
or a number of keys in combination only when that hour is reached.
Another very interesting device is the _automatic combination_ lock.
This may have twenty or more keys, any one of which can lock it; but the
same one must be used to _un_lock it, as the key automatically sets the
mechanism in favour of itself. With such a lock it would be possible to
have a different key for every day in the month; and if any one key got
into wrong hands it would be useless unless it happened to be the one
which last locked the lock.
[Illustration: FIG. 221.--The wrong key inserted. The pins do not allow
the lock to be turned.]
* * * * *
THE CYCLE.
There are a few features of this useful and in some ways wonderful
contrivance which should be noticed. First,
THE GEARING OF A CYCLE.
To a good many people the expression "geared to 70 inches," or 65, or
80, as the case may be, conveys nothing except the fact that the higher
the gear the faster one ought to be able to travel. Let us therefore
examine the meaning of such a phrase before going farther.
The safety cycle is always "geared up"--that is, one turn of the pedals
will turn the rear wheel more than once. To get the exact ratio of
turning speed we count the teeth on the big chain-wheel, and the teeth
on the small chain-wheel attached to the hub of the rear wheel, and
divide the former by the latter. To take an example:--The teeth are 75
and 30 in number respectively; the ratio of speed therefore = 75/30 =
5/2 = 2-1/2. One turn of the pedal turns the rear wheel 2-1/2 times. The
gear of the cycle is calculated by multiplying this result by the
diameter of the rear wheel in inches. Thus a 28-inch wheel would in this
case give a gear of 2-1/2 × 28 = 70 inches.
One turn of the pedals on a machine of this gear would propel the rider
as far as if he were on a high "ordinary" with the pedals attached
directly to a wheel 70 inches in diameter. The gearing is raised or
lowered by altering the number ratio of the teeth on the two
chain-wheels. If for the 30-tooth wheel we substituted one of 25 teeth
the gearing would be--
75/25 × 28 inches = 84 inches.
A handy formula to remember is, gearing = T/_t_ × D, where T = teeth on
large chain-wheel; _t_ = teeth on small chain-wheel; and D = diameter of
driving-wheel in inches.
Two of the most important improvements recently added to the cycle
are--(1) The free wheel; (2) the change-speed gear.
THE FREE WHEEL
is a device for enabling the driving-wheel to overrun the pedals when
the rider ceases pedalling; it renders the driving-wheel "free" of the
driving gear. It is a ratchet specially suited for this kind of work.
From among the many patterns now marketed we select the Micrometer
free-wheel hub (Fig. 222), which is extremely simple. The
_ratchet-wheel_ R is attached to the hub of the driving-wheel. The small
chain-wheel (or "chain-ring," as it is often called) turns outside this,
on a number of balls running in a groove chased in the neck of the
ratchet. Between these two parts are the _pawls_, of half-moon shape.
The driving-wheel is assumed to be on the further side of the ratchet.
To propel the cycle the chain-ring is turned in a clockwise direction.
Three out of the six pawls at once engage with notches in the ratchet,
and are held tightly in place by the pressure of the chain-ring on their
rear ends. The other three are in a midway position.
[Illustration: FIG. 222.]
When the rider ceases to pedal, the chain-ring becomes stationary, but
the ratchet continues to revolve. The pawls offer no resistance to the
ratchet teeth, which push them up into the semicircular recesses in the
chain-ring. Each one rises as it passes over a tooth. It is obvious
that driving power cannot be transmitted again to the road wheel until
the chain-wheel is turned fast enough to overtake the ratchet.
THE CHANGE-SPEED GEAR.
A gain in speed means a loss in power, and _vice versâ_. By gearing-up a
cycle we are able to make the driving-wheel revolve faster than the
pedals, but at the expense of control over the driving-wheel. A
high-geared cycle is fast on the level, but a bad hill-climber. The
low-geared machine shows to disadvantage on the flat, but is a good
hill-climber. Similarly, the express engine must have large
driving-wheels, the goods engine small driving-wheels, to perform their
special functions properly.
In order to travel fast over level country, and yet be able to mount
hills without undue exertion, we must be able to do what the motorist
does--change gear. Two-speed and three-speed gears are now very commonly
fitted to cycles. They all work on the same principle, that of the
epicyclic train of cog-wheels, the mechanisms being so devised that the
hub turns more slowly than, at the same speed as, or faster than the
small chain-wheel,[42] according to the wish of the rider.
We do not propose to do more here than explain the principle of the
epicyclic train, which means "a wheel on (or running round) a wheel."
Lay a footrule on the table and roll a cylinder along it by the aid of a
second rule, parallel to the first, but resting on the cylinder. It will
be found that, while the cylinder advances six inches, the upper rule
advances twice that distance. In the absence of friction the work done
by the agent moving the upper rule is equal to that done in overcoming
the force which opposes the forward motion of the cylinder; and as the
distance through which the cylinder advances is only half that through
which the upper rule advances, it follows that the _force_ which must
act on the upper rule is only half as great as that overcome in moving
the cylinder. The carter makes use of this principle when he puts his
hand to the top of a wheel to help his cart over an obstacle.
[Illustration: FIG. 223.]
[Illustration: FIG. 224.]
[Illustration: FIG. 225.]
Now see how this principle is applied to the change-speed gear. The
lower rule is replaced by a cog-wheel, C (Fig. 223); the cylinder by a
cog, B, running round it; and the upper rule by a ring, A, with internal
teeth. We may suppose that A is the chain-ring, B a cog mounted on a pin
projecting from the hub, and C a cog attached to the fixed axle. It is
evident that B will not move so fast round C as A does. The amount by
which A will get ahead of B can be calculated easily. We begin with the
wheels in the position shown in Fig. 223. A point, I, on A is exactly
over the topmost point of C. For the sake of convenience we will first
assume that instead of B running round C, B is revolved on its axis for
one complete revolution in a clockwise direction, and that A and C move
as in Fig. 224. If B has 10 teeth, C 30, and A 40, A will have been
moved 10/40 = 1/4 of a revolution in a clockwise direction, and C 10/30
= 1/3 of a revolution in an anti-clockwise direction.
Now, coming back to what actually does happen, we shall be able to
understand how far A rotates round C relatively to the motion of B, when
C is fixed and B rolls (Fig. 225). B advances 1/3 of distance round C; A
advances 1/3 + 1/4 = 7/12 of distance round B. The fractions, if reduced
to a common denominator, are as 4:7, and this is equivalent to 40
(number of teeth on A): 40 + 30 (teeth on A + teeth on C.)
To leave the reader with a very clear idea we will summarize the matter
thus:--If T = number of teeth on A, _t_ = number of teeth on C, then
movement of A: movement of B:: T + _t_: T.
Here is a two-speed hub. Let us count the teeth. The chain-ring (= A)
has 64 internal teeth, and the central cog (= C) on the axle has 16
teeth. There are four cogs (= B) equally spaced, running on pins
projecting from the hub-shell between A and C. How much faster than B
does A run round C? Apply the formula:--Motion of A: motion of B:: 64 +
16: 64. That is, while A revolves once, B and the hub and the
driving-wheel will revolve only 64/80 = 4/5 of a turn. To use scientific
language, B revolves 20 per cent. slower than A.
This is the gearing we use for hill-climbing. On the level we want the
driving-wheel to turn as fast as, or faster than, the chain-ring. To
make it turn at the same rate, both A and C must revolve together. In
one well-known gear this is effected by sliding C along the spindle of
the wheel till it disengages itself from the spindle, and one end locks
with the plate which carries A. Since B is now being pulled round at the
bottom as well as the top, it cannot rotate on its own axis any longer,
and the whole train revolves _solidly_--that is, while A turns through a
circle B does the same.
To get an _increase_ of gearing, matters must be so arranged that the
drive is transmitted from the chain-wheel to B, and from A to the hub.
While B describes a circle, A and the driving-wheel turn through a
circle and a part of a circle--that is, the driving-wheel revolves
faster than the hub. Given the same number of teeth as before, the
proportional rates will be A = 80, B = 64, so that the gear _rises_ 25
per cent.
By means of proper mechanism the power is transmitted in a three-speed
gear either (1) from chain-wheel to A, A to B, B to wheel = _low_ gear;
or (2) from chain-wheel to A and C simultaneously = solid, normal, or
_middle_ gear; or (3) from chain-wheel to B, B to A, A to wheel = _high_
gear. In two-speed gears either 1 or 3 is omitted.
* * * * *
AGRICULTURAL MACHINES.
THE THRESHING-MACHINE.
Bread would not be so cheap as it is were the flail still the only means
of separating the grain from the straw. What the cream separator has
done for the dairy industry (p. 384), the threshing-machine has done for
agriculture. A page or two ought therefore to be spared for this useful
invention.
[Illustration: FIG. 226.--Section of a threshing machine.]
In Fig. 226 a very complete fore-and-aft section of the machine is
given. After the bands of the sheaves have been cut, the latter are fed
into the mouth of the _drum_ A by the feeder, who stands in the
feeding-box on the top of the machine. The drum revolves at a very high
velocity, and is fitted with fluted beaters which act against a steel
concave, or breastwork, B, the grain being threshed out of the straw in
passing between the two. The breastwork is provided with open wires,
through which most of the threshed grain, cavings (short straws), and
chaff passes on to a sloping board. The straw is flung forward on to the
shakers C, which gradually move the straw towards the open end and throw
it off. Any grain, etc., that has escaped the drum falls through the
shakers on to D, and works backwards to the _caving riddles_, or moving
sieves, E. The _main blower_, by means of a revolving fan, N, sends air
along the channel X upwards through these riddles, blowing the short
straws away to the left. The grain, husks, and dust fall through E on to
G, over the end of which they fall on to the _chaff riddle_, H. A second
column of air from the blower drives the chaff away. The heavy grain,
seeds, dust, etc., fall on to I, J, and K in turn, and are shaken until
only the grain remains to pass along L to the elevator bottom, M. An
endless band with cups attached to it scoops up the grain, carries it
aloft, and shoots it into hopper P. It then goes through the shakers Q,
R, is dusted by the _back end blower_, S, and slides down T into the
open end of the rotary screen-drum U, which is mounted on the slope, so
that as it turns the grain travels gradually along it. The first half of
the screen has wires set closely together. All the small grain that
falls through this, called "thirds," passes into a hopper, and is
collected in a sack attached to the hopper mouth. The "seconds" fall
through the second half of the drum, more widely spaced, into their
sack; and the "firsts" fall out of the end and through a third spout.
MOWING-MACHINES.
[Illustration: FIG. 227.]
The ordinary _lawn--mower_ employs a revolving reel, built up of
spirally-arranged knives, the edges of which pass very close to a sharp
plate projecting from the frame of the mower. Each blade, as it turns,
works along the plate, giving a shearing cut to any grass that may be
caught between the two cutting edges. The action is that of a pair of
scissors (Fig. 227), one blade representing the fixed, the other the
moving knife. If you place a cylinder of wood in the scissors it will be
driven forward by the closing of the blades, and be marked by them as
it passes along the edges. The same thing happens with grass, which is
so soft that it is cut right through.
HAY-CUTTER.
The _hay-cutter_ is another adaptation of the same principle. A
cutter-bar is pulled rapidly backwards and forwards in a frame which
runs a few inches above the ground by a crank driven by the wheels
through gearing. To the front edge of the bar are attached by one side a
number of triangular knives. The frame carries an equal number of spikes
pointing forward horizontally. Through slots in these the cutter-bar
works, and its knives give a drawing cut to grass caught between them
and the sides of the spikes.
* * * * *
SOME NATURAL PHENOMENA.
WHY SUN-HEAT VARIES IN INTENSITY.
The more squarely parallel heat-rays strike a surface the greater will
be the number that can affect that surface. This is evident from Figs.
228, 229, where A B is an equal distance in both cases. The nearer the
sun is to the horizon, the more obliquely do its rays strike the earth.
Hence midday is necessarily warmer than the evening, and the tropics,
where the sun stands overhead, are hotter than the temperate zones,
where, even in summer at midday, the rays fall more or less on the
slant.
[Illustration: FIG. 228.]
[Illustration: FIG. 229.]
The atmospheric envelope which encompasses the earth tends to increase
the effect of obliquity, since a slanting ray has to travel further
through it and is robbed of more heat than a vertical ray.
THE TIDES.
All bodies have an attraction for one another. The earth attracts the
moon, and the moon attracts the earth. Now, though the effect of this
attraction is not visible as regards the solid part of the globe, it is
strongly manifested by the water which covers a large portion of the
earth's surface. The moon attracts the water most powerfully at two
points, that nearest to it and that furthest away from it; as shown on
an exaggerated scale in Fig. 230. Since the earth and the water revolve
as one mass daily on their axis, every point on the circumference would
be daily nearest to and furthest from the moon at regular intervals, and
wherever there is ocean there would be two tides in that period, were
the moon stationary as regards the earth. (It should be clearly
understood that the tides are not great currents, but mere thickenings
of the watery envelope. The inrush of the tide is due to the temporary
rise of level.)
[Illustration: FIG. 230.]
[Illustration: FIG. 231.]
WHY HIGH TIDE VARIES DAILY.
The moon travels round the earth once in twenty-eight days. In Fig. 231
the point _a_ is nearest the moon at, say, twelve noon. At the end of
twenty-four hours it will have arrived at the same position by the
compass, but yet not be nearest to the moon, which has in that period
moved on 1/28th of a revolution round the earth.[43] Consequently high
tide will not occur till _a_ has reached position _b_ and overtaken the
moon, as it were, which takes about an hour on the average. This
explains why high tide occurs at intervals of more than twelve hours.
[Illustration: FIG. 232.--Relative positions of sun, moon, and earth at
"spring" tides.]
[Illustration: FIG. 233.--Relative positions of sun, moon, and earth at
"neap" tides.]
NEAP TIDES AND SPRING TIDES.
The sun, as well as the moon, attracts the ocean, but with less power,
owing to its being so much further away. At certain periods of the
month, sun, earth, and moon are all in line. Sun and moon then pull
together, and we get the highest, or _spring_ tides (Fig. 232). When sun
and moon pull at right angles to one another--namely, at the first and
third quarters--the excrescence caused by the moon is flattened (Fig.
233), and we get the lowest, or _neap_ tides.
[39] In both Figs. 207 and 208 the degree of expansion is very greatly
exaggerated.
[40] As the sun passes the meridian (twelve o'clock, noon) the
chronometer's reading is taken, and the longitude, or distance east or
west of Greenwich, is reckoned by the difference in time between local
noon and that of the chronometer.
[41] For much of the information given here about clocks and watches the
author is indebted to "The History of Watches," by Mr. J.F. Kendal.
[42] We shall here notice only those gears which are included in the hub
of the driving-wheel.
[43] The original position of the moon is indicated by the dotted
circle.
INDEX.
NOTE.--Figures in italics signify that an illustration of the thing
referred to appears on the page.
Aberration, spherical, of lens, 243.
Acoustics, 294.
Achromatic lens, 243.
Action carriage of piano, 283.
Advancing the spark, 102.
Air-gun, _342_.
Air-pump for cycle tyres, _340_;
for Westinghouse brake, 199.
Alternating currents, 164;
dynamo, 164.
Amperage, 125.
Angle of advance, 57, 58;
incidence, 268;
reflection, 268.
Aorta, 360.
Arc lamp, 182.
Archimedes, 412.
Armature, 162.
Arteries, 358.
Arterial blood, 359.
Atmospheric pressure, 350.
Auditory nerve, 272.
Automatic brakes, 188;
signalling, 228;
stoker, 399.
Backfall, 298.
Balance-wheel, 419.
Ball cock, 366, _367_.
Balloon, fire, 323;
gas, 347.
Barometer, aneroid, 328, _329_;
and weather, 331;
Fortin's, _326_;
meaning of, 325;
simple, _328_;
wheel, _327_.
Beau de Rochas, 89.
Bell, diving, _332_;
electric, 119, _120_.
Bellows of organ, 303.
Bioscope, 266.
Blades, turbine, _81_, 83.
Block system, 201, 212.
Blood, arterial, 359;
circulation of, _356_, _357_, 360;
venous, 359.
Blower-plate, 393, _394_.
Boat, sails of, 346.
Boiler, Babcock and Wilcox, _21_, 22;
explosions, 34, 391;
fire-tube, 21;
fittings, 31;
Lancashire, 25, _26_;
locomotive, _20_, 23;
multitubular, 21;
principle of, 15;
stored energy in, 32;
vertical, _25_;
water supply to, 39;
water-tube, 21.
Brakes, hydraulic, 188;
motor car, 110;
railway, 187;
vacuum, 189, _190_, _191_;
Westinghouse, 194, _195_, _197_.
Bramah, 363, 437.
Breezes, land and sea, 324.
Brushes of dynamo, 161, _172_.
Bunsen burner, 409.
Burning-glass, 232.
Camera, the, 233;
pinhole, _234_, _235_.
Canals, semicircular, 273.
Capillary attraction, 392;
veins, 358.
Carbon dioxide, 27, 359;
monoxide, 27.
Carburetter, 98, _99_.
Cardan shaft, 93.
_Carmania_, the, 83.
Centrifugal force, 382.
Change-speed gear, 105, 442.
Chassis of motor car, 92.
Circulation of water in a boiler, _17_, _18_, _19_;
of water in a motor car, 95, _97_.
Clarionet, 308.
Clock, first weight-driven, 412;
water, 410.
Clutch of motor car, 105.
Coal, as fuel, 15;
gas, 394;
gas making, 394;
gas plant, _396_;
gas, purification of, 397.
Cochlea, 273.
Coherer, 140.
Coil, Ruhmkorff, 121.
Coke, 395.
Combinations in Chubb lock, 436;
Yale lock, 436.
Combustion, 26, 393;
perfect, 28.
Compensating gear, 107, _108_.
Compound engines, 59;
arrangement of, 61;
invention of, 59.
Compound locomotives, 62.
Compound microscope, 261.
Condenser, marine, 71, _72_;
of Ruhmkorff coil, 123.
Conduit, 176.
Convex lens, image cast by, _236_.
Conjugate foci, 262.
Cornet, 308.
Corti, rods of, 274.
Coxwell, 348.
Cream separator, 381, _383_.
Current, reversal of electric, _130_, 131;
transformation of, 124.
Cushioning of steam, 55.
Cycle, gearing of, 439.
Cylinder, hydraulic press, _363_;
steam, _49_.
Danes, 382.
Dead point, 47.
De Brouwer stoker, 401.
Detector in Chubb lock, 435.
Diving-bell, _332_;
simple, _333_, _334_.
Diving-dress, 335.
Direction of current in dynamo circuit, 163.
Diver's feats, 338;
helmet, _336_;
lamp, _338_.
Donkey-engines, 68.
Doorstop, self-closing, 344.
Double-cylinder engines, 47.
Draught, forced, 28, _29_;
induced, 29.
Drum and fusee, _414_.
Durability of motor-car engine, 96.
D-valve, 67.
Dynamo, alternating, 164, 174;
brushes, _172_;
compound, 174;
continuous-current, 165;
multipolar, 169;
series wound, _173_;
shunt wound, _173_;
simple, 161, _162_.
Ear, the, _271_, _273_;
a good, 274, 307;
sensitiveness of, 275.
Eccentric, _52_, 53;
setting of, 53.
Edison, Thomas, 310.
Edison-Bell phonograph, 310.
Electricity, current, 115;
forms of, 113;
nature of, 112;
static, 114.
Electric bell, 119, _120_;
signalling, 225;
slot, 226.
Electroplating, 185, _186_.
Electro-magnets, 117.
Endolymph, 272.
Engines, compound, 59;
donkey, 68;
double-cylinder, 47;
internal-combustion, 87, 95;
reciprocating, 44.
Escapement of timepieces, 416;
cylinder, _420_;
lever, 421, _422_.
Ether, 270.
Eustachian tube, 276.
Eye, human, 246, _247_;
self-accommodation of, 248.
Expansive working of steam, 56.
Faraday, Michael, 159.
Field, magnetic, 159;
magnets, 171;
ring, 174.
Filters, 374;
Maignen, _373_;
Berkefeld, 374.
Filtration beds, 372.
Flute, 308.
Flying-machines, 348.
Fly-wheel, use of, 48.
Focus, meaning of, 237;
principal, 238.
Foci, conjugate, 262.
Force, lines of, 116.
Forces, component, 345.
Free wheel, _440_.
Furring-up of pipes, 391.
Fusee, drum and, 414.
Galileo, 259, 325, 416.
Galilean telescope, _259_.
Gas, coal, 394;
governor, 402;
meter, 405;
traps, 374;
works, 394.
Gasometer, 397;
largest, _398_, 399.
Gauge, steam, 36, _38_;
water, 35, _36_.
Gear, compensating, 107, _108_.
Gear-box of motor car, 105.
Gearing of cycle, 439.
Glaisher, 348.
Gland, 50, 363.
Glass, flint and crown, 242.
Going-barrel for watches, 415.
Gooch reversing gear, 65.
Governors, speed, 67;
of motor car, 103, _104_.
Graham, 418.
Gramophone, 317;
records, 319, 321;
reproducer, _318_.
Hairspring, 412.
Hay-cutter, 451.
Heart, the, 355;
disease, 361;
rate of pulsation of, 361;
size of, 357.
Heat of sun, 451.
Hele, Peter, 412.
Helmet, diver's, _336_.
Helmholtz, 274, 308.
Hero of Alexandria, 74.
Herschel, 261.
Hertz, Dr., 138.
Hertzian waves, 138.
Hot-water supply, 386.
Hour-hand train in timepieces, _429_.
Household water supply, 364.
Hughes type-printer, 134.
Hydraulic press, 361, _362_.
Hydro, 385.
Ignition of charge in motor-car cylinder, 100, _101_.
Image and object, relative positions of, 239;
distortion of, 245.
Incandescent gas mantle, 407;
electric lamp, 179.
Incus, 272.
Index mechanism of water-meter, 37.
Indicator of electric bell, 119.
Induction coil, 121;
uses of, 125.
Injector, 39;
Giffard's, _41_;
principle of, 40;
self-starting, 42.
Interlocking of signals, 204, 222.
Internal-combustion engine, 87.
Iris of eye, 249;
stop, 249.
Kelvin, Lord, 158.
Keyless winding mechanism, 425, _426_, 428.
Kite, 345.
Lamp, arc, 182;
how it works, 392;
incandescent, 179;
manufacture of incandescent lamps, 180.
Lap of slide-valve, _57_, 59.
Larynx, 306.
Laxey wheel, _380_, 381.
Leads, 208.
Lenses, 231;
correction of for colour, 240, _241_;
focus of, 236;
rectilinear, _245_;
spherical aberration in, 243.
Levers, signal, colours of, 208.
Limit of error in cylinder, 52.
Light, electric, 179;
nature of, 230;
propagation of, 231.
Li Hung Chang, 157.
Lindsay, James Bowman, 145.
Lines of force, 116, 162.
"Linking up," 65.
Locks, 430;
Barron, 433;
Bramah, 437;
Chubb, 433, 434;
Hobbs, 437;
simplest, _431_;
tumbler, _432_;
Yale, _436_.
Locking gear for signals, 205.
Locomotive, electric, 178;
advantages of, 179.
Lungs, 359.
Magic-lantern, 263, _264_.
Magnet, 115;
permanent, 115, 116;
temporary, 115.
Magnetism, 115.
Magnetic needle, influence of current on, 129.
Mainspring, invention of, 412.
Malleus, 272.
Marconi, 140, 146.
Marine chronometers, 415;
delicacy of, 425.
Marine speed governor, 71.
Marine turbine, advantages of, 84.
Maudslay, Henry, 363.
Maxim, Sir Hiram, 348.
Micrometer free wheel, 441.
Micro-photography, 265.
Microscope, 254;
compound, 261, _263_;
in telescope, 257;
simple, _254_.
Mineral oil, 392.
Mirror, parabolic, 261, _262_;
plane, _267_.
Morse, 132, 145;
code, 128;
inker, 142;
sounder, 132.
Motor car, the, 92;
electric, 177.
Mouth, 307.
Mowing-machines, 450.
Musical sounds, 277.
Nerve, auditory, 272;
optic, 246.
Nodes on a string, 285;
column of air, 291.
Note, fundamental, 285;
quality of, 285.
Niagara Falls, power station at, 174.
Organ, the, 294, _300_;
bellows, 303;
console, 305;
echo, solo, swell, great, and choir, 301;
electric and pneumatic, 305;
largest in the world, 306;
pedals, 298;
pipes, 295;
pipes, arrangement of, 295;
sound-board, _296_;
wind-chest, 297.
Otto cycle, 91.
Overtones, 285.
Pallets of organ, 297.
Parallel arrangement of electric lamps, 184.
Paris, siege of, 265.
Pedals of organ, 298.
Pelton wheel, _377_.
Pendulum, 412;
compensating, 418, _419_.
Perilymph, 272.
Perry, Professor, 16.
Petrol, 98.
Phonograph, 310;
governor, _311_;
recorder, 312, _313_;
records, making of, 319;
reproducer, 315;
tracings on record of, _317_.
Pianoforte, 277;
sounding-board, 280;
striking mechanism, 281;
strings, 281.
Piccolo, 308.
Pipes, closed, 289;
flue, 301;
open, 292;
organ, 295;
reed, 301, _302_;
tuning, 302.
Piston valve, 67.
Pneumatic tyres, 341.
Poldhu, signalling station at, 138.
Points, railway, 208, _210_;
and signals in combination, 211.
Poles of a magnet, 115.
Popoff, Professor A., 138, 145.
Power, transmission of, 175.
Preece, Sir William, 145.
Primary winding of induction coil, 122.
Pump, air, 340;
bucket, 352, _353_;
force, 354;
most marvellous, 355;
Westinghouse air, 199.
Railway brakes, 187;
signalling, 200.
Rays, converging and diverging, _256_;
heat, concentrated by lens, _232_;
light, 232, 235, 236, 237.
Records, master, 319, 320.
Reciprocation, 51.
Reed, human, 306;
pipes, 301, _302_.
Reflecting telescope, 260.
Relays, telegraphic, 133, 141.
Retina, 247.
Retorts, 395.
Reversing gear, 62;
Allan, 65;
Gooch, 65;
radial, 66.
Rocking bar mechanism for watches, 425.
Rods of Corti, 274.
Ruhmkorff coil, 121, _122_.
Safety-valve, 32, _33_, 391.
Sand-glasses, 411.
Scissors, action of, _450_.
Secondary winding of induction coil, 122.
Series arrangement of electric lamps, 183.
Series winding of dynamo, _173_.
Shunt wound dynamo, _173_.
Sight, long and short, 250.
Signalling, automatic, 228;
electric, 225;
pneumatic, 225;
power, 225.
Signal levers, _206_.
Signals, interlocking of, 204;
position of, 202;
railway, 200;
single line, 215.
Silencer on motor cars, 109.
Siphon, _351_.
Slide-valve, 49, 50, 51;
setting of, 53.
Sliders, 297.
Sound, nature of, 270;
board of organ, 296;
board of piano, 280.
Spagnoletti disc instrument, 212.
Sparking-plug, _102_.
Spectacles, use of, 249.
Spectrum, colours of, 230.
Speed governors, 67, _68_, _69_;
Hartwell, 70;
marine, 71.
Speed of motor cars, 110.
Spot, blind, in eye, 251;
yellow, in eye, 251.
Spring balance for watches, 419;
compensating, 423, _424_.
Stapes, 272.
Steam, what it is, 13;
energy of, 14;
engines, 44;
engines, reciprocating, _45_;
expansive working of, 59, 81;
gauge, 36;
gauge, principle of, 37;
turbine, 74;
turbine, De Laval, 76, _77_;
turbine, Hero's, 74;
turbine, Parsons, 79, _80_;
volume of, as compared with water, 15.
Stephenson, George, 63, 375.
Stop, in lens, 244;
iris, 249;
use of, 244.
Sun-dial of Ahaz, 410.
Syntonic transmission of wireless messages, 143.
Talking-machines, 310.
Tapper in wireless telegraphy receiver, 141.
Tappet arm, 205.
Telegraph, electric, 127;
insulator, _133_;
needle, _128_;
recording, 133;
sounder, 132.
Telegraphy, high-speed, 135;
wireless, 137.
Telephone, 147;
Bell, _148_;
circuit, double-line, 155;
circuit, general arrangement, _152_, 153;
exchange, _154_, 155.
Telephony, submarine, 157.
Telescope, 257;
Galilean, _259_;
prismatic, _260_;
reflecting, 260;
terrestrial, _259_.
Threshing-machine, 447, _448_.
Thurston, Professor, 31.
Tides, 452;
high, 453;
neap and spring, 455.
Timbre, 285.
Tompion, Thomas, 412.
Torricelli, 325.
Trachea, 306.
Train staff signalling, 216;
single, 216;
and ticket, 217;
electric, 218.
Transformation of current, 124, 176.
Transmission of power, 174, _175_.
Transmitter, Edison telephone, 150;
granular carbon, 150, _151_.
Triple-valve, 196.
Trolley arm, 176.
Turbines, steam, 74.
_Turbinia_, the, 79.
Tympanum, 137, 271, 272.
Universal joint, 93.
Vacuum brake, 189, _190_, _191_.
Vacuum chamber of aneroid barometer, _330_.
Valve, piston, 67;
safety, 32;
of internal-combustion engine, 89.
Valves of the heart, 357.
Veins, 358;
capillary, 358;
pulmonary, 361.
Ventral segments, 291.
Ventricles, 357.
Vibration of columns of air, 288, 289;
of rods, 287;
of strings, 278;
of strings, conditions regulating, 278.
_Viper_, the, 86.
Virag, Pollak--high-speed telegraphy, 136.
Vitreous humour, 246.
Voltage, 121, 161.
Vowel sounds, 308.
Wasborough, Matthew, 51.
Watches, first, 412.
Water cock, _365_;
engines, 375;
gauge, 35, _36_;
jacket, 19, 95;
meter, _368_;
supply, 371;
turbines, 174, 376;
wheels, 375.
Watt, James, 51, 69, 375.
Welsbach incandescent mantle, 407.
Westinghouse air-brake, 194, _195_, _197_;
George, 194.
Wheatstone needle instrument, 128, 131;
automatic transmitter, 135.
Wind, why it blows, 323;
action of on kites, 345;
on sails, 346.
Windmills, 375.
Window, oval, in ear, 272;
round, in ear, 272.
Wireless telegraphy, 137;
advance of, 145;
receiver, 140, 141;
syntonic, 143;
transmitter, 138, _139_.
Yale lock, _436_, _437_.
Yellow spot, in eye, 251.
Zech, Jacob, 414.
Zeiss field-glasses, 260.
THE END.