L O 
With regard to the lock which Mr. Bramah prefents 
to the public as abfolutely perfect, he informs us, that the 
idea'of conftrufting it was firft fuggefted by the alarming 
increafe of houfe-robberies, which may reafonably be fup- 
pofed to be perpetrated in a great meafure by perfidious 
fervants, or accomplifiied by their connivance. Thus it 
is evident, that the locks which might exclude ordinary 
houfebreakers could be no fecurity againft faithlefs fer¬ 
vants, who, having conftant accefs to the locks, might ea- 
fily get falfe keys fabricated at their leifure. In confider- 
ing the fubjeft, our author was convinced, that his hope 
of fuccels depended entirely upon his ufing means as dif- 
fimilar as poffible to thofe by which the old locks were 
conftrufted ; as thefe, however varied, had been found in- 
fufficient for the purpofe. “As nothing (fays he) can be 
more oppofite in principle to fixed, wards than a lock which 
derives its properties from the motion of all its parts, I de¬ 
termined that the conftruftion of fuch a lock (liould be 
the fubjeft of tny experiment.” In the profecution of 
this experiment he had the fatisfaftion to find, that the 
lealt perfect of all his models fully afcertained the truth 
$nd certainty of his principle. The exclufion of wards 
made it neceflary to cut off all communication between 
the key and the bolt; as the fame paffage, which (in a 
lock jimply conftrufted) would admit the key, might give 
admiffion likewife to other inftruments. The office, there¬ 
fore, which in other locks is performed by the extreme 
point of the key, is here affigned to a lever, which cannot 
approach the bolt til! every part of the lock has under¬ 
gone a change of pofition. The neceffity of this change 
to the purpoles of the lock, and the abfolute impoffibility 
of effefting it otherwife than with the proper key, are the 
points to be afcertained j and this is effected in the fol¬ 
lowing manner. 
Fig. i fliows Mr. Bramah’s firft attempt to conftruft a 
lock upon this principle: which, to his furprife, turned 
out complete and perfect. A reprefents a common axis 
en which the fix levers, eroding the face of the lock, are 
united as on a joint. Each of thefe refts upon a feparate 
fpring fufficiently ltrong to bear its weight; or, if de- 
preffed by a fuperior force, to reftore it to its proper po¬ 
sition when that force is removed. B reprefents a frame 
through which the levers pafs by feparate grooves, ex¬ 
actly fitted to their width, but of fufficient depth to al¬ 
low them a free motion in a perpendicular direftion. The 
part which projects from the oppofite fide of the joint A, 
and is inferted in the bolt C, is a lever to which two of¬ 
fices are affigned ; one to keep the bolt in a fixed pofition, 
in the abfence of the key; the other, to give it its proper 
motion upon the application of the key. D D is a circu¬ 
lar platform turning upon a centre. On this the joint 
or carriage of the levers, and the fpring 3 on which 
they reft, are fixed; and the motion of this platform im¬ 
pels the bolt, in either direction, by means of the lever 
which is projected from the joint A. The inviolable re- 
ftraint upon this lock, by which means it is fubjefted only 
to the aftion of the key, is lodged in the part E, which is 
a thin plate, bearing at each extremity on a block, and 
having of courfe a vacant fpace beneath, equal in height 
to the thicknefs of the blocks on which it refts. By this 
plate the motion of the machine is checked or guided in 
the following manner: On the edge of the plate which 
faces the movement there are fix notches which receive 
the ends of the levers projefting beyond the frame B ; and 
while they are confined in this manner the motion of the 
machine is fo totally fufpended as to defy every power of 
art to overcome. To underftand in what manner the pro¬ 
per key of this lock overcomes thefe obftacles, it ir.uit be 
obferved, that each lever has a notch on -its extremity, 
and that thofe notches are difpofed as irregularly as poffi- 
ble. To give the machine a capacity of motion, thefe 
notches mull; be brought parallel to each other, and, by a 
diftinft but unequal preffure upon the levers, be formed 
into a groove in a direft- line with the edge of the plate 
E, which the notches are exaftly fitted to receive. The 
Vol. XII. No. 87*. 
C K. 8fl§ 
leaf! motion of the machine, while the levers are in this 
pofition, will introduce the edge of the plate into the 
groove ; which, controuling the power of the fprings, will 
give liberty to the levers to move in a horizontal direc¬ 
tion as far as the fpace between the blocks which fupport 
the plate E will admit, and which is fufficient to give the 
machine a power of acting on the bolt. The impoffibi¬ 
lity of thus bringing the notches on the points of the le¬ 
vers into a direft line, fo as to tally with the edge of the 
plate E by any other means than the motion and impulfe 
of the key, is that which conftitutes the principal excel¬ 
lence of this lock. 
The key, fig. 2, exhibits fix different furfaces, againft 
which the levers are progreffively admitted in the opera¬ 
tion of opening the lock; the irregularity of thefe fur- 
faces fliows the unequal and diftinft degree of preffure 
which each lever requires to bring them to their proper 
bearings, in order to put the machine in motion. Hence 
it appears, that, unlefs the various heights of the furfaces 
expreffed cn the bit of the key are exaftly proportioned 
to the feveral diftances neceffary to bring the notches into 
a ftraight line with each other, they mull remain immova¬ 
ble ; and (fays our author), as one ftroke of a file is fuffi¬ 
cient to caufe fuch a difproportion as will prove an in- 
furmountable impediment to their motion, I may fafely 
aftert, that it is not in art to produce a key or other in- 
ftruinent, by which a lock, conftrufted upon this princi¬ 
ple, can be opened.” On this principle it would even 
be a matter of great difficulty for any workman, however 
fkilful, to conftruft a key for the lock when open to his 
infpeftion : “for the levers being raifed, by the fubjacent 
fprings, to an equal height in the frame B, prefent a plane 
furface; and confequently convey no direction that can 
be of any ufe in forming a tally to the irregular furface 
which they prefent when acting in fubjeftion to the key.” 
Unlefs therefore we can contrive a method to bring the 
notches on the points of the levers in a direft lin<% with 
each other, and to retain them in that pofition till an ex- 
aft impreffion of the irregular furface, which the levers 
will then exhibit, can be taken ; the workman will be 
unable to fit a key to the lock, or to move the bolt. This 
procefs mult be rendered extremely troublefonie by means 
of the fprings; and, if fuch difficulties occur even when 
the lock is open to the infpeftion of a fkilful workman, 
much more mult we fuppofe it out of the power of one 
who has not accefs to the internal parts to make a falfe 
key to a lock of this kind. Thefe difficulties render it 
neceflary, in making locks of this kind, not to fit the key 
to the lock, as is ulual in other locks, but to fit the lock 
to the key. In this kind of lock, therefore, the key mult 
be made firft ; and the inequalities upon the furface of 
the bit worked as chance or fancy may direft, without 
any reference to the lock. The key being thus completed, 
and applied to the furface of the levers, will, by a gentle 
preffure, force them to unequal diftances from their com¬ 
mon ftation in the frame B, and fink their points to un¬ 
equal depths into the fpace beneath the plate E. While 
the levers are in this pofition, the edge of the plate E will 
mark the precife point at which the notch on each lefrer 
mud be exprelled. The notches being cut by this direc¬ 
tion, the irregularity which appears when the levers re- 
fume their ltatioa in the frame B, and the inequality of 
the receffes on the bit of tiie key, will appear, as a feal and 
its correfponding impreffion. 
The following is a lock contrived upon the fame prin¬ 
ciple, but more curious, and, in our author’s opinion, 
more extenfively ufeful. Fig. 3 reprefents a circular 
block of metal divided from the centre into eight com¬ 
partments, eacli containing a cell whjcli forms a paffage 
through tiie block, as is reprefented by the fmall "circles 
defcribed on the flat furface A. In each of thefe cells 
two grooves are cut at oppofite points, which open a com¬ 
munication with tire centre at one point, and with the 
fpherical furface of the block or barrel at the other, The 
fmall circle, which marks the centre of the fiat furface A, 
10 M is 
