870 L O € K. 
is the key-hole, which likewife forms a paflage through the 
barrel in a parallel line with the cells which furround it. 
This figure reprefents the frame, in which the aftive parts 
of the lock are depofited. Fig. 4 fliows a fpiral fpring 
lodged in the bottom of each cell, and occupying one half 
of the fpace, the other being filled with a Aider relling 
upon the fpring, and reprefented by fig. 5, the oftice of 
thefe Aiders exaftly correfponding with that of the levers 
in the Jock already defcribed. Thus, when lodged in their 
refpeftive cells, they are fuftained, like the levers, by the 
ela-fticity of the fprings upon which they reft, till a Supe¬ 
rior power is applied; and they are again reftored to their 
Rations by the re-aftion of the fprings when the weight 
is removed. The fideB of each Aider is projected beyond 
the circular furface/ as reprefented fig. 6 , in a manner 
fimilar to the projection of the levers in the former lock, 
beyond the curved frame in which they move. The point 
C, fig. 3, is projected through the interior groove into the 
fpace which forms the centre or key-hole, expreffed on 
the flat furface A. Fig. 7 reprefents the key. When 
this is applied, it muff of courfe encounter thefe interior 
projections; and,when prefled forward, the indented fpaces 
on its point, being unequal, will force the Aiders to unequal 
distances from their bearers; bringing the notches ex- 
prefled on their exterior projections in a direCt line with 
each other, in a manner fimilar to that by which the ef- 
feCt is produced upon the levers in the former lock. 
When the key is withdrawn, and the Aiders refume their 
ftations by the preflure of the fprings, the difpofition of 
the notches mult be irregular in the fame proportion that 
the indentations on the point of the key are unequal; 
and they muft neceflarily fall again into a ftraight line 
when aCted upon by the key. 
Fig. 6 fliows the barrel completely fitted for aCtion. Its 
interior end is capped with a plate, which unites its com¬ 
partments, and confines the fprings and Aiders within the 
cells to which they belong. From that plate proceeds the 
point A, which reprefents the lever by which the bolt is 
projected or withdrawn, according to the direction in 
which the machine performs its revolution. The parts 
of the movement being thus united, the interior end of 
the barrel is depofited in a bed reprefented fig. 3 . The 
ftation of the bolt is at A ; the lever which afts upon it 
being projected on the other fide. 
On this lock our author obferves, that it is excellent for 
ftreet-doors ; “ for no method of robbery (fays he) is more 
praCtifed, than gaining admittance info houfes by thofe 
keys, which, as is well known, may be procured at the old 
iron Aiops to fit almoft any lock in ufe. Such robberies 
are generally committed where the lervants are allowed to 
take the key with them when fent on errands, it being 
impracticable while the key is left in the lock. The va¬ 
riations, by which the production of correfpondent keys 
is avoided, have two iources; the one arifing from the 
changes that may be made in the difpofition of the le¬ 
vers ; the other from the number of points contained on 
the projected furface of each lever; by which the pofition 
cf its notch may, in the fmalleft degree, be varied. The 
variations produceable in the difpofitions of fix figures 
only, are 720 ; thefe, being progreflively multiplied by ad¬ 
ditional figures, will increafe by aftonifiiing degrees; and 
eventually fliow, that a lock containing twelve levers will 
admit of 479,001,500 changes ; which, with the addition 
of another lever, will increafe to 6,227,020,800. Thefe 
being again multiplied by the number of changes which 
the projected furface of the levers will admit in the dif¬ 
pofition of the notches, their amount wiil exceed nume¬ 
ration, and may therefore be properly faid to be infinite. 
The flighted inflection will at once fliow, that their con- 
ftruCtion precludes all poflibility of obtaining an impref- 
lion of their internal parts, which is neceflary for the fa¬ 
brication of a falfe key ; for it will beeafily feen, that the 
politions into which the levers are forced by the preflure 
of the key in opening the lock, can no more.be afcer- 
uined when the key is withdrawn, than the feal can be 
copied from its impreffion oh a fluid, or the courfe of a 
fliip be difcovered by tracing it on the furface of the 
waves. But inviolable fecurity is not the only excellence 
they poffefs ; the fimplicity of their principle gives them 
likewife a great advantage over locks that are more com¬ 
plicated, in point of duration ; for, their effential parts be¬ 
ing fubjeCt to no friction, nor expofed to any poflible ac¬ 
cident from without, they will be lefs affeCted by ufe, and 
lefs liable to Hand in need of repair.” 
Mr. Bramah’s locks may be arranged fo as to require a 
new and different key in cafe the original ftiould be loft 
or ftolen; for this purpofe the lock muft be opened, and 
the Aiders taken out and changed into different grooves; 
a new key muft now be made, with the grooves of the 
fame depth as the original key, but arranged in a differ¬ 
ent order, correfponding with the new arrangement of the 
Aiders. The old key will not now open the lock. An¬ 
other great advantage of thefe locks is, that, from the cir- 
cumftance before explained of the bolt having no aftion. 
to turn the barrel, though the barrel has a great power to> 
flioot the bolt, a ftrong lock may have but a very fmall 
key. For inftance, the bolt of the lock at fig. 1 is of 
great ftrength, while the key, fig. 2, is fo fmall, that it may 
be earrjed fufpended to the watch-chain; and then it will 
not be in danger of being loft or miflaid, fo as to give op¬ 
portunity for ill-difpofed perfons to make a falfe key from 
it, unknown to the owner. 
Fir. Bramah’s locks continue to be mod generally in 
ufe, though others difplaying great ingenuity have been 
brought forward at different times. For fome of thefe 
patents have been obtained, as that of Mr. Spears, de¬ 
fcribed in the viiith volume of the Repertory of Arts. 
Others have been at once generoufiy given to the public ; 
and accounts of them may be feen in the Tranfa£tions of 
the Society for the Encouragement of Arts, &c. particu¬ 
larly in vols. iii. xviii. xix. xxiii. We {hall devote the re¬ 
maining fpace of the prefent Engraving to a defcription 
of Mr. Timothy Marfhall’s fecret efcutcheon, from the 
third volume (now fcarce) of thofe Tranfaftions. 
The marquis of Worcefter appears to have invented 
fome fecret efcutcheons ; for, in his Century of In ventions, 
publifhed in 1663, at N° 72, after having fpoken of three 
kinds of locks invented by him, he fays, “An efcutcheon 
to be placed before any of thefe locks with thefe proper¬ 
ties: The owner, though a woman, may with her delicate 
hand vary the ways of coming to open the lock ten mil¬ 
lion times beyond the knowledge of the fmith that made 
it, or of me w'ho invented it.” 
Many attempts have been made to form a machine equal 
in its properties to the defcription here given; and from 
thence, it is probable, arofe the kind of padlocks which 
have been long made in this country, in great numbers, 
which, having feveral letters on different rings, can only be 
opened when a certain fet of thofe letters is arranged in one 
order; but this was in nodegree equal to the end propofed ; 
for, befides the workman who made it being at all times 
informed of the pofition the letters muft be in, and confe- 
quently enabled to open it, the letters and rings admit¬ 
ting of no variation of place, at the will of the owner 5 
referving, at the fame time, a power of opening the lock; 
whenever the proper arrangement became known, the fe¬ 
cret was divulged, and all lecurity at an end; but, by the 
improvement made by Mr. Marfliall, the letters or figures 
allowing an almoft infinite variety of changes, the owner 
may, in one minute, alter the fecret in fucii a manner, 
that even the maker would be as unlikely fo open it as 
he would be of gaining the higheii prize in a lottery by 
the chance of a fingle ticket. Thus this kind of efcut- 
cheon is infinitely more fecure than any hitherto in ufe, 
efpecialty as the alteration of the letters may be made 
every day for years, without recurring to their firlt (fate; 
and, as the ow ner may at one time chooic to truft a friend 
or a domeftic with the fecret, lb that they might have re- 
courfe to his valuables, See. he may alio at another time 
with to exclude them from that privilege, which this con- 
3 ' trivance 
