ON TUMBLER, OR LEVER LOCKS.
Security being the primary object in all locks, any considerations as to
mechanical ingenuity and graceful decoration give place to those which
relate to safety. A spring lock may be ingenious and even beautiful in
its construction, but an imitative key will easily open it. Hence arose
the invention of wheels or wards; and as wards failed in
trustworthiness, they in their turn yielded to something better. We have
already explained how the insecurity of mere warded locks arises; and we
shall have something more to say on the subject in a future chapter. It
is sufficient here to remark, that wards, springs, screws, alarums,
wheel-work, escutcheons,--all, however useful for particular purposes,
are wanting in the degree of surety which we require in a lock. Hence
the invention of _tumblers_, _levers_, or _latches_, which fall into the
bolt and prevent it from being shot until they have been raised or
released by the action of the key. We have been unable to ascertain at
what time, or in what country, or by whom, tumbler-locks were invented.
The invention has been claimed by or for persons subsequently to the
year 1767, when the celebrated French treatise (_Art du Serrurier_)
already referred to was published; and yet this treatise contains
numerous examples of simple tumbler locks of ingenious construction, as
will presently be shewn.
[Illustration: fig. 17. Simple tumbler lock.]
One of the most elementary forms of tumbler-lock is shewn in fig. 17. In
this case the bolt, instead of having two notches in the bottom edge,
like those in the back-spring lock, fig. 6, has two square notches or
slots in the upper edge; and as the key acts upon the bolt, these
notches must of course share in whatever movements the bolt is subjected
to. Behind the bolt is a kind of latch or tumbler (the lower part of
which is shewn by dotted lines), with a stump or projecting piece of
metal at _a_; the tumbler moves freely on a pivot at the other end, and
is made to rise through a small arc whenever the key acts upon the bolt.
When the bolt is wholly shot, the stump falls into one notch and
prevents the motion of the bolt; when wholly unshot or withdrawn, the
stump falls into the other notch, and equally prevents the motion of the
bolt. It is not, therefore, until the key, by elevating the tumbler, has
raised the stump out of the notch, that the bolt has freedom of
movement. If the shape of the key does not enable its web to effect this
elevation to a sufficient degree, the bolt remains immovable; and to
this extent a certain additional security is obtained by making the
shape of the key significant as well as the wards.
[Illustration: fig. 18.]
[Illustration: fig. 19. Old French lock.]
The tumbler-principle, as we have said, is difficult to trace to its
origin on account of the various aspects which it presents; but the
great French treatise proves that the locksmiths of France were familiar
with tumbler-locks a century ago. The plates of that work represent the
details of numerous locks, on the upper edge of the bolts of which were
notches called _encoches_, as at _o k_ fig. 18; into these notches sank
a small iron stud or stump called the _arrêt du pêne_, or bolt-stop,
shewn in fig. 19, attached to the upper portion of the _gâchette_ or
tumbler, which, for the sake of economy of metal, is made in the form of
a triangular spring in front of the bolt _k i_; and not until the key,
by its circular action, had raised this stud out of one or other of the
notches, could the bolt move to the right or left. The stud was
generally fixed to a spring which forced it down again into the notch as
soon as the action of the key had ceased. Sometimes, however, the stud
was fixed to the bolt, and the notches were in a separate tumbler or
_gâchette_ (see E E, fig. 21); and in other instances, again, the stump
was fixed to the case of the lock and caught into notches in the bolt.
It will be seen, when we come to treat of tumbler-locks of later date,
that there was much in these early locks to point out the way. Fig. 19,
copied from the French work, represents a lock of the box or casket
kind. Two staples, fixed into the cover, fall into two cavities or
receptacles at C _d_; and a short bolt in each receptacle catches into
each staple, one near _g_ and one near _h_. The small bolt _q_ is
attached to the upper extremity of the lever _q r s_, fig. 19, and shewn
separately in fig. 20; and by the pressure of a spring _a_ (fig. 19)
upon this lever, the bolt _q_ is kept locked in the staple. The
vertical portion of this spring presses at its lower end on another
spring _p_ (fig. 19) of singular curvature; and attached to the
horizontal part of this second spring is the stud, which falls into a
notch in the top of the bolt. The action of these parts, then, is as
follows: when the key is placed upon the key-pin at Z, and turned round
in the direction in which the hands of a watch move, the bitt presses
against the tail _s_ of the lever, moves it upon its centre Z, fig. 19,
_v_, fig. 20, to the left, and consequently moves the upper part _q_ to
the right, drawing it out of the receptacle and liberating the staple
within C. Thus it will be seen that the lever _q r s_, held in one
position by the spring _a_, forms in itself a simple kind of spring
catch-lock, and was, in fact, formerly used as such, without any other
appendages except the staple in the lever, into which the catch _q_
fitted on shutting down the lid. So also we may regard the other
portion, fig. 18, or _k i p h_ (fig. 19), as forming a separate lock;
for the key after having passed S comes in contact with the triangular
spring, which it raises thereby, lifting the stud out of the bolt, and
exerting pressure against the barbs of the bolt _n_. Fig. 18 shoots the
bolt _k_, and also the short bolt _l_, which passes through the staple
in the cavity _d_, fig. 19.
[Illustration: fig. 20.]
The lock represented in the four following figures is also from M. de
Réaumur’s chapter on locks in the work referred to. In this lock the
tumbler-principle is carried out in a very elaborate manner, for not
only is the stump or stud H (fig. 23) attached to a very strong spring
(best shewn at H, fig. 22), which holds it with considerable force in
one of the three notches of the principal bolt R S (fig. 24); but there
is also a second set of notches E E in the _gâchette_ G O (fig. 21), and
a pin attached to one of the plates of the lock fits into one of these
notches, thereby preventing the bolt from being moved until the
_gâchette_ is lowered by the revolution of the key; so that in
attempting to pick this lock, not only must the spring H be raised so as
to release the stud from the notches of the great bolt, but the
_gâchette_ must be lowered to disengage the fixed pin from the notches.
There is yet a third source of security. Attached to the large bolt are
short projecting pins F (fig. 21), against which an arm or detent, G F,
of the _gâchette_ projects, thus preventing the bolt from being shot
back by any pressure applied to its extremity S.
[Illustration: fig. 21. Details of an old French lock.]
[Illustration: fig. 22. Another view of the same.]
[Illustration: fig. 23. Another view of the same.]
[Illustration: fig. 24. The two bolts detached.]
There are a few details relating to this remarkable lock, which may as
well be introduced here in order to complete the description. The
principal bolt can be shot twice, or be _double-locked_; hence it is
furnished with three barbs for the key to act against, and with three
notches for the spring-stud. The lower bolt I K can be shot by the
horizontal pressure of the button P (figs. 22, 23), which is situated on
the inner side of the door to which this lock is attached, so that a
person inside the room can secure the door against any one on the
outside who is not furnished with the proper key, for it must be
remarked that the small bolt as well as the large one is acted on by the
key. Now supposing the small bolt to be shot or locked, it is kept so by
the pressure of the coiled spring Q (figs. 21, 22). But this small bolt
is connected with the large one by means of the bent lever O N M (figs.
21, 24), which turns on a pin N attached to the main bolt. Now, when
both bolts are either fully shot or unshot, the arm O N lies flat
against and parallel with the main bolt; but when the large bolt is
unshot and the small one not moved, the arms O N, N M, fall into an
inclined position, and the arm O N passing a little below the main bolt
comes within the range of the web of the key, which in its revolution
causes the bent lever to move upon its centre N, thereby restoring O N
to its horizontal position, and at the same time causing the arm N M to
move from right to left, or in the direction for unshooting the small
bolt; the end of this arm thus catches into a mortise V (figs. 21, 24)
in the small bolt, and immediately unlocks it.
But to return to the subject of tumbler-locks. About the year 1778, Mr.
Barron introduced that species of double-action (as it may perhaps be
termed) which so greatly increases the security of the simple tumbler,
fig. 17. In the tumbler-locks previously made, if the tumbler were
raised sufficiently high, the lock could be opened: there was no such
possibility as raising it _too_ high; but Mr. Barron, by his invention,
patented 31st October, 1778, rendered it absolutely necessary that a
limit should be put to the height to which the tumbler should be raised,
by rendering the bolt equally immovable whether the tumbler were too
much or too little raised. Another important improvement was the
introduction of two tumblers instead of one. The bolt has in its middle
a slot or gating notched on both edges, the notches being fitted for the
reception of studs fixed to the tumblers. Supposing the studs or stumps
of the tumblers to be resting in the lower notches, they require to be
elevated to the general level of the gating before the bolt can be
moved; whereas, on the other hand, if the tumblers were raised ever so
little too high, the studs will enter the upper notches, and prevent the
shooting of the bolt. The lower edge, or belly, of each tumbler is acted
on by the steps of the key during its circular movement; the leverage of
the key being so exactly adjusted as to raise the tumbler to the desired
height and no further. The tumblers are made unequally wide, so that
steps or inequalities in the bit of the key are requisite to lift them
both to the proper height. There are thus two improvements introduced:
there are two tumblers instead of one, and each tumbler has a double
instead of a single action.
This ingenious and very useful lock is represented, so far as regards
its governing principle, in fig. 25. The bolt is here seen to have a
peculiar slot or hole cut in it, consisting of a narrow horizontal
passage or gating, with three notches above it and three below it. These
double notches might be available even for one tumbler only; but Barron
used two or more for the sake of additional security. In fig. 25 there
are two tumblers shewn, expressed by dotted lines; both are hinged to
one pivot, both are raised by the same action of the key, but the stump
on the one tumbler does not coincide in position with that on the other.
It will be seen that if the studs of the tumblers rested in the lower
notches, they would require to be elevated to the level of the gating
before the bolt could be moved; while, on the other hand, if lifted too
high, the stumps would be caught in the upper notches, and would equally
prevent the passage of the bolt, The tumblers are unequally wide; and
the bitt of the key is stepped or notched in a corresponding way, that
there may be one step fitted to act upon each tumbler. Mr. Barron also
adopted the reverse arrangement of having the stump on the bolt, and the
openings in the tumblers; so that the principle of his patent may be
concisely expressed as being “an arrangement to allow a stump on the
tumbler to pass through an opening in the bolt, or a stump on the bolt
to pass through an opening in the tumbler.”
[Illustration: fig. 25. Action of Barron’s tumbler-lock.]
A very elaborate tumbler-lock, patented 23d February, 1790, by Mr.
Rowntree, contrasts remarkably with the simplicity of Barron’s lock. Mr.
Rowntree’s lock consisted of tumblers combined with revolving discs or
wheels. Its mechanism may be understood from the following description
and engravings. The same letters refer to the same parts in the several
figures.
[Illustration: fig. 26.
fig. 27.
fig. 28.
fig. 29.
fig. 30.
Details of Rowntree’s tumbler-lock.]
A A is the plate which encloses the whole mechanism of the lock, and
fastens it to the door; B B is the bolt, guided in its motion by sliding
under the bridges C D; E E are pillars which support a plate covering
the works; F are the circular wards surrounding the centre or key-pin;
and _a_ shews the position of the key, which, in turning round, acts in
a notch _r_ in the bolt, and propels it; G, the tumbler, is a plate
situated beneath the bolt, and moving on a centre-pin at _d_; it has a
catch or stump _e_ projecting upwards, which enters the notches _s_ or
_g_ in the bolt, and thereby retains the latter for backward or forward
motion, as the case may be; H is a spring which presses the tumbler
forward. The key _a_, in turning round, acts first against the part _c
c_ of the tumbler, and raises it so as to remove the stump from the
notches; it can then enter the notch _r_ in the bolt, and move it. So
far there is no particular security; but Mr. Rowntree sought to obtain
it by the following means. There is a piece of metal _h_ fixed to the
lower side of the tumbler, called the _pin_; when the tumbler is caught
in either notch of the bolt, the pin applies itself to a cluster of
small wheels I, fitted on one centre-pin beneath the tumbler; the edges
of these wheels stop the pin, and prevent the tumbler from being raised.
But each wheel has a notch cut in its circumference I; and it is only
when the wheels are so placed that all their notches lie in a right
line, that the pin can enter this compound notch and allow the tumbler
to rise. The wheels must therefore be all adjusted to position; and this
is effected by a number of levers K centred on one pin at _k_; at the
opposite end each lever has a tooth _m_ entering a notch in the wheel
belonging to it; so that when any lever is pressed outward, it turns its
wheel round. Now this pressure of the levers is brought about by a
spring _n_ applied to each; and when so pressed, the levers rest against
a pin _o_ fixed in the plate. The key is so cut as to determine the
extent to which the levers shall act upon the wheels. The key first
operates from the curved part _p p_ of the levers K, and raising them,
turns all the wheels I at once into the proper positions; in turning
further round, it then operates on the part _c c_ of the tumbler,
causing the latter to rise and to release the bolt; and in turning still
further round, it (the key) seizes the notch _r_ of the bolt, and shoots
it. The key is cut into steps of different lengths, as shewn at V V;
each step operates on its respective lever K in a different degree from
the others; the notch at _s_ acts upon the tumbler, and the plain part
_t_ moves the bolt.
We now proceed to notice the modern tumbler-lock. This was arranged by
Bird, whose patent, bearing date 29th October, 1790, was for a series of
four double-acting tumblers, differing in no respect from those patented
by Barron, and closely resembling those in use at the present time in
the best tumbler-locks. We will describe the modern tumbler-lock more
particularly when we have gone through a few historical details on the
subject.
Messrs. Mitchell and Lawton obtained a patent bearing date 7th March,
1815, for a lock in which were combined with the bolt and double-acting
tumblers, a series of movable wards, and a revolving curtain for closing
the key-hole. The action of the wards was peculiar. On introducing any
key or instrument, and passing it round, a number of movable wards or
pieces were thrown out so as to prevent the key from being turned back
or withdrawn. It was necessary therefore to pass round the key so as to
unlock the lock, and if that were not possible, as in the case of a
false key being used, it was held permanently, and could only be
released by destroying the lock, When the bolt was once shot, the wards
were carried up so as to leave a clear passage for the key. This lock
does not appear ever to have come into use, on account of the violence
required in case a wrong key should be used either by accident or
design.
The detention of a wrong key in this lock appears to have suggested the
contrivance of a _detector_. This was first made by Ruxton, whose patent
is dated 14th May, 1816. His detectors were of various kinds, the object
of each kind being to give information to the owner in case any one of
the tumblers should be overlifted in an attempt to pick the lock, which
fact would be discovered on the next application of the true key. This
is precisely the object of the detector in tumbler-locks at the present
day, and Ruxton accomplished it by somewhat similar means. He also had a
contrivance for holding a false key, as in Mitchell and Lawton’s lock;
and he recommended this form of detector in the following words: “It is
true that in this case the lock will have to be destroyed in order to
open the door: the result is frightful; but we think the more terrible
the result, the less likely would any one be to tamper with it.”
We now come to Chubb’s lock, patented 3d February, 1818, which consisted
of double-acting tumblers and a peculiar kind of detector. This lock has
been made the subject of various patents obtained in the years 1824,
1833, 1846, and 1847. This lock[4] consists of six separate and distinct
double-acting tumblers, all of which must be raised to a particular
height, neither more nor less, in order that the bolt may pass. It also
comprises a _detector_, by which, should any one of the tumblers be
lifted too high in an attempt to pick or open the lock by a false key,
it would be immediately detected on the next application of the proper
key. The tumblers are flat pieces of iron or steel, with the plane of
the surface vertical, and pivoted at one end; and the following is the
mode in which the key, the tumblers, and the bolt, are brought into
mutual action.
[4] The lock about to be described is the latest and most complete
form of Chubb lock up to the date of the Great Exhibition. The various
additions and alterations which have been made in the lock since that
date will be noticed in a subsequent chapter.
The bolt shoots in and out of the lock in the usual way. It has a square
stud or stump riveted on one surface; and it is to furnish obstructions
to the passage of this stud that the tumblers are provided. All the six
tumblers are pivoted to one pin at the end, giving to each of them a
small leverage, each independent of the others. There are six springs
which press these tumblers downwards, one to each tumbler. There is a
longitudinal slot or gating in each tumbler, large enough to receive the
stud of the bolt; and unless all the six slots (supposing there to be
six tumblers) coincide in height or position, the stud will not have a
clear passage for moving to and fro. Now the slots are purposely made
nearer the upper edge in some of the tumblers than in others, all the
six being different in this respect; so that if they are all lifted
_equally_, the slots do not coincide, and the bolt and its stud will not
pass. The tumblers must then be raised _unequally_, those to be most
raised which have the slot nearest to the lower edge. To effect this,
the bit of the key is cut into six steps or inequalities, each to act
upon one particular tumbler, and each cut or stepped to the exact depth
which will suffice for the proper raising of the tumbler. The key is
inserted in the keyhole, and is turned; the six steps raise the six
tumblers all to the proper height, to leave a clear passage along the
slots; and the extreme end of the key then acts upon the bolt itself,
and shoots it. To unlock it again, the same or a duplicate key must be
used; for if another key be employed, differing by ever so little from
the proper one, some one or more of the tumblers will be lifted either
a little too much or not quite enough; and in either case the stud of
the bolt will catch above or below the slot, instead of having a clear
line of movement along the slot itself. After both locking and
unlocking, the springs force the tumblers down as far as they can go,
burying the stud in the recesses above the slot; so that the tumblers
must be raised by the key both for locking and unlocking.
The doctrine of chances has wide play in determining the relative
position of the six tumblers. In Mr. Chubb’s essay this part of the
subject is treated in the following way: “The number of changes which
may be effected on the keys of a three-inch drawer-lock is 1 × 2 × 3 × 4
× 5 × 6 = 720, the number of different combinations which may be made on
the six steps of unequal lengths (on a six-tumbler lock), without
altering the length of either step. The height of the shortest step is,
however, capable of being reduced 20 times; and each time of being
reduced, the 720 combinations may be repeated; therefore 720 × 20 =
14,400 changes. The same process, after reducing the shortest step as
much as possible, may be gone through with each of the other five steps;
therefore 14,400 × 6 = 86,400, which is the number of changes that can
be produced on the six steps. If, however, the seventh step, which
throws the bolt, be taken into account, the reduction of it only ten
times would give 86,400 × 10 = 864,000, as the number of changes on
locks with the keys all of one size (that is, with one key of definite
size in all save the lengths of the steps). Moreover, the drill pins of
the locks and the pipes of the keys may be easily made of three
different sizes; and the number of changes will then be 864,000 × 3 =
2,592,000, as the whole series of changes which may be gone through with
this key. In smaller keys, the steps of which are capable of being
reduced only ten times, and the bolt-step only five times, the number of
combinations will be 720 × 10 × 6 × 5 × 3 = 648,000. On the other hand,
in larger keys, the steps of which can be reduced thirty times, and the
bolt-step twenty times, the total number of combinations will be 720 ×
30 × 6 × 20 × 3 = 7,776,000.”
These enormous numbers have been the cause of much of the wonderment
which the six-tumbler locks have excited; and, as we shall see further
on, the Bramah lock presents still more of the marvellous in respect to
this ringing of the changes.
[Illustration: fig. 31. Chubb lock, with detector and six tumblers.]
The construction and action of the Chubb lock may be further illustrated
by means of an engraving, fig. 31, in which _b_ is the bolt of the lock,
with a stump riveted to it marked _s_. The six tumblers are shewn
perspectively, the front or anterior one being marked _t_; they all move
on the centre-pin _a_, but are nevertheless perfectly distinct and
separate, to allow of being elevated to different heights. At _d_ is
shewn one end of a divided spring, the divisions being equal to the
number of tumblers, one to each, and so bent that each spring may press
upon its particular tumbler. At _e_ is the detector-spring, so placed
that a projecting piece in the hindmost tumbler shall be near it; this
tumbler having also fixed into it a stud or pin _p_. This being the
arrangement, especially in relation to the stump _s_ and the tumblers,
it follows that all the tumblers must be lifted to exact and regulated
heights in order that the stump may pass through the longitudinal slits
of the tumblers; unless it can do so, the bolt cannot be withdrawn. As
there are gaps or notches in each tumbler both above and below the
proper line of passage, and as there are no ordinary means of
ascertaining when any one tumbler is lifted too high or not high enough,
the safety of the lock is greatly increased by this uncertainty;
especially when it is considered that this uncertainty is multiplied
sixfold by the different modes in which the six tumblers are slotted.
If, through the insertion of a false key, or by any other cause, any one
of the tumblers be raised above its proper position, the detector spring
_e_ will catch the hindmost tumbler, and retain it so as to prevent the
bolt from passing; and thus, upon the next application of the true key,
it will be instantly felt that some one of the tumblers has been
overlifted, because the true key will not unlock it. To relieve the bolt
from this temporary imprisonment, the key must be turned the reverse
way, as for locking; all the tumblers will thus be brought to their
proper position, and allow the stump to enter the notches _n n´_; the
bevelled part of the bolt will then lift up the detector-spring, and
allow the hindmost tumbler to fall down into its proper place; and all
this being effected, the lock may be opened and shut in the ordinary
way. The pin _p_ is so adjusted that if any one of the tumblers--front,
back, or intermediate--be lifted too high, the pin will be lifted with
it, and will catch into the detector-spring, thus producing the result
just described.
[Illustration: fig. 32.
Key to Chubb’s lock.]
The key is represented in fig. 32. It has six steps, besides a terminal
step to act upon the bolt. The height of each step, or the distance to
which it extends from the pipe of the key, depends of course on the
height to which its corresponding tumbler is to be lifted; and it
matters not whether the steps of the key are adjusted to the slots of
the tumblers, or the slots to the steps, provided the agreement be
brought about. It is simply a matter of manufacturing convenience that
the key-steps are cut first and the tumbler-slots afterwards. We may
here remark that _bit_, or _bitt_, is the name given, somewhat
indefinitely, either to the whole flat part of a key, or to the small
stepped portions of it. The flat part was formerly termed the _web_ of
the key, probably from the _webbed_ appearance of the keys to complex
warded locks.
After the reading of Mr. Chubb’s paper before the Institution of Civil
Engineers, Mr. Owen narrated one or two circumstances connected with the
early history of Chubb’s lock. A convict on board one of the
prison-ships at Portsmouth dockyard, who was by profession a lock-maker,
and who had been employed in London in making and repairing locks for
several years, and subsequently had been notorious for picking locks,
asserted that he had picked with ease one of the best of Bramah’s locks,
and that he could pick Chubb’s locks with equal facility. One of the
latter was secured by the seals of the late Sir George Grey, the
Commissioner, and some of the principal officers of the dockyard, and
given to the convict, together with files and all the tools which he
stated were necessary for preparing false instruments for the purpose,
as also blank keys to fit the pin of the lock. A lock exactly the same
in principle was placed in his hands, that he might examine it and make
himself master of its construction. If he succeeded in opening the lock,
he was to receive a free pardon from the Government, and a reward of
100_l._ from Messrs. Chubb. After trying for two or three months to pick
the sealed lock--during which time, by his repeated efforts, he
frequently over-lifted the detector, which was as often re-adjusted for
his subsequent trials--he gave up the attempt. He stated that Chubb’s
were the most secure locks he had ever met with, and that it was
impossible for any man to pick or to open them with false instruments.
Mr. Owen further stated, that in order to compare the merits of Bramah’s
and Chubb’s locks, he had suggested a mechanical contrivance, which was
applied to one of Bramah’s six-spring padlocks belonging to the Excise.
It was hung upon a nail, in a vertical position, secure from lateral
oscillation. A self-acting apparatus was then applied, consisting of a
pipe with hexagonal grooves, and a stud or bit corresponding with the
division of the lock, and secured to it by a spring. In the grooves of
this pipe small slides were inserted, which pressed against the spring
keys of the lock; to these slides were attached levers, acted upon by
eccentrics, moved by a combination of wheels, whose teeth differed in
number so as to perform the permutation required for the different
depths of the spring keys, corresponding with those of the proper key to
the lock. The automaton machine was set in motion by a line working over
a barrel, and acted upon by a weight; and was thus left acting upon the
mechanism for a considerable time. At right angles to the pipe or false
key was attached a rod and weight; and when the notches in the spring
keys were brought in a line with the plane of the plate or diaphragm of
the lock, the rod and weight turned the false key, opened the lock, and
stopped the further motion of the automaton. In that state the slides
indicated the exact depth of the grooves in the proper key, and gave the
form of a matrix by which to make a key similar to the original one. The
automaton worked during a period varying from half an hour to three
hours, according to the state of permutation of the apparatus at the
moment of being applied, compared with that of the slides in the lock.
We confess that it is difficult to understand the action of this
automaton from Mr. Owen’s description. We imagine that the false notches
would effectually prevent the operation of the instrument, and openings
would be required on each slide to bring it back, so as to meet the
motions of the machine.
Mr. Owen did not state whether his apparatus had been successful with
one only of Bramah’s locks or with several; nor did he describe any
apparatus invented with the view to the picking of Chubb’s locks. He
stated, however, that in order to ascertain the effect of friction on
one of these last-named locks, it was subjected to the alternate
rectilinear motion of a steam-engine in Portsmouth dockyard, and was
locked and unlocked upwards of 460,000 times consecutively, without any
appreciable wear being indicated by a gauge applied to the levers and
the key, both before and after this alternate action. Mr. Owen concluded
by expressing his individual opinion that Chubb’s lock had never been
picked. “The detector was the main feature of its excellence; and
additional precaution, therefore, was only departing from its
simplicity, and adding to the expense, without any commensurate
advantage.”
In a subsequent chapter the degree of security afforded by various
descriptions of locks, and the obstacles which they present of being
picked, will come under notice; we therefore now proceed to describe
briefly a few other tumbler-locks, or application of the
tumbler-principle.
In Mr. Somerford’s lock, for which the Society of Arts gave a premium in
1818, an attempt was made to improve upon the ordinary action of
tumblers. In most such locks, all the tumblers must ascend, although to
different heights, before the stud of the bolt can pass through the
slots; “which arrangement,” says Mr. Somerford, “gives an opportunity of
introducing a nail, or a piece of stout wire, into the lock, and thus
raising the tumblers without the necessity of using the key.” In his new
lock, however, he made one lever to ascend while the other descended, by
a somewhat complicated arrangement of slotted plates above and below the
bolt. The key was so perforated as to be much endangered in respect to
strength.
In Davis’s lock there is a double chamber with wards on the side of the
key-hole. The key is inserted into the first chamber and turned a
quarter round; it is then pushed forward into the inner chamber, where
there is a rotating plate containing a series of small pins or studs,
which are laid hold of by the key. By turning the key, the plate is
moved round, the tumbler is raised, and the bolt is shot backwards and
forwards. This lock, which is somewhat expensive, is used to some extent
on Cabinet despatch-boxes.
The lock invented by Mr. Nettlefold is so constructed, that when the
bolt is shot out by the key, two teeth or quadrants are projected from
the sides of the bolt, which take a firm hold of the plate fixed on the
door-post or edge. This construction is said to answer well for
sliding-doors.
Mr. Alfred Ainger, in 1820, received a silver medal from the Society of
Arts for a draw-back spring latch, in which the objects proposed were
the two following--to render the lock more difficult of violation by a
pick than those ordinarily in use; and to apply to it a key of which no
ordinary person could take an impress, and which would be difficult of
access even in a workman’s hand. The key is very peculiar; its pipe
consists of three divisions, the section of the upper and lower
divisions being circular, and that of the middle division triangular;
the triangular portion is intended to give motion to some part of the
interior of the lock during the rotation of the key. There are collars
fixed on the extremity of the key, to act each on one tumbler; and there
are modes, by varying the arrangement of these collars on an octagonal
stem, to give something like a permutation to the number of variations
to which the action of the key may be subject. The notches or slots are
rather in the bolt than in the tumblers; and there are many
peculiarities in the general arrangement.
In a lock invented and patented by Mr. Parsons, the tumblers are of a
particular form, being hinged on a pivot at their centres, and working
into and out of two notches cut in the under side of the bolt. It must
be obvious that many variations in the adjustment of the tumblers of
locks might be made, without vitiating the principle on which the action
depends.
Many inventors have tried the use of an expanding web to the key, so
planned that if the step of the web be long enough to reach the tumbler,
it would be too long to pass through the key-hole; and therefore a
principle of safety would operate by enabling the key to adjust itself
at one moment to the size of the key-hole, and at another to the height
of the tumbler. Mr. Machin of Wolverhampton invented such a key in 1827.
The web of the key is movable on a countersunk pin, on which it can so
far slide as to be drawn one-eighth of an inch from the barrel. The
key-hole is of such a size as to admit the key only when the web is
pressed close up to the barrel. When the key in this state is
introduced, and is begun to be turned round, one of the notches in the
web works into a raised circular edge of steel, placed eccentrically
with regard to the lock-pin; so that as the key is turned, the web
becomes drawn out, and is at its greatest elongation when it arrives at
the tumblers: in the second half of its circular movement, the key
becomes contracted to its original dimensions, and can then be removed
from the lock.
Another mode of modifying the key has been introduced by Mr. Mackinnon,
the object being to enable any person to change at will the pattern or
arrangement of the movable parts of a lock and key; or to keep the key,
when not actually in use, in such a state as to render it unavailing to
any one but himself. It was a complex arrangement, which does not seem
to have come much into use.
The lock invented by Mr. Williams, in 1839, may be designated a
pin-lock, involving a principle analogous in many points to that of the
Egyptian lock. This lock has a series of pins which reach through the
cap, and are pressed to their places with a key like a comb or a
rake-head. On the inner end of each pin is a flat piece of steel, in
which is cut a notch for the passage of the bolt; but this passage is
not clear until the notches in all the pieces of steel are in a right
line. The pins are movable, and can be pushed either too far or not far
enough to bring about the coincidence of position in the notches; and on
this ground they are “double-acting.” Now the teeth of the key are of
irregular lengths, each having a length just suited for pushing the pin
to the proper depth: any other lengths of teeth would fail to open the
lock. There is a mechanism of springs and levers to shoot the bolt when
the pins in the plate are rightly adjusted. The arrangements in respect
to the key are singular and somewhat awkward. The teeth which lock the
bolt are not the same as those which unlock it, the user having to
change ends and adjust the bit to a socket-handle. This is one among
many examples in which a lock embodies several principles, the inventor
having set himself the task of combining the excellences of many diverse
locks.
In respect to the tumbler-locks generally, the simplicity of action, the
strength of construction, and the non-liability of disarrangement, have
given them a high place among safety-locks. The only danger seemed to
be, that any person once obtaining possession of the key could take an
impression from it, and thence form a key which would command the lock.
Attempts have been occasionally made to obviate this danger, by
supplying the key with movable bits which could be changed at pleasure,
so as to constitute any number of effectively different bits in
succession. But the locks being so constructed that the bolt could only
be moved when the tumblers were in a certain position, the owner was
placed in this predicament: that it was useless to alter the arrangement
of the bits in the key, unless the tumblers were altered in a
corresponding manner; and this would entail the removal of the lock from
the door, and the re-arrangement of the interior mechanism.
One of the great defects of tumbler-locks made previously to the last
ten years was, that the tumblers, when lying at rest in the lock,
presented at their _bellies_ or lower edges precisely the same
arrangement as the steps of the key. Indeed, in many locks of the
present day, a good idea of the form of the key may be gained by feeling
the bellies of the tumblers. The bellies are in fact cut out so as to
compensate for the circular motion of the key, to allow them to remain
at rest while the stump is passing through the gating. Even in
tumbler-locks of the best construction the tumblers will vibrate more or
less during the motion of the key; a defect which must be provided
against in adjusting the lock, or the stump will be caught in its
passage through the gating. Mr. Hobbs provides a simple remedy by
enlarging the back part of the gating, the effect of which is as
follows: when, in shooting back the bolt, as in unlocking, the key has
got to its highest point, the stump enters the narrow end of the gating;
but in shooting the bolt forward, as in locking, the stump enters the
gating before the key has got to its highest point, and to allow for the
slight vibratory motion of the tumblers during the passage of the stump,
the gating is widened. The usual method of adjustment is to alter the
forms of the bellies of the tumblers, thus greatly risking the security
of the lock, a defect which was clearly perceived by Bramah [see pp.
67-70], and was one of the reasons which induced him to construct locks
with slides instead of tumblers.
American locks on the tumbler-principle, and the relation which all such
locks bear to the Bramah lock, will be better understood after the
details of the following chapter.