the Society, for the infpection of the Public.

Defcription of the Plate of Mr. Marshall's Secret Escutcheon.

A, the barrel in which the bar B slides: part of this barrel is concealed within the rollers, but the ends of it appear at a and b, fig. 1.

B, the bar with projecting teeth by which the rollers C prevent its being drawn back till the nick in the recefs is brought exactly over the tooth: the square end of this bar is feen at c, fig. 2.

C, a roller, of which there are five, each composed of two circles, the outer circle having four rows of letters at equal distances engraved on its furface, with small knobs, for the more commodiously turning the rollers round, the inner circle D being movable within the outer one on the barrel A: to the furface of each of the inner circles, is faftened a small fpring,

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fpring, d ferving to keep the outer circle in its place, till an alteration in the pofition of the letters which are the foundation of the fecret, is intended to be made ; and within the inner circle is a recefs to prevent the bar B being drawn back, unless the teeth and the nick are in their proper fituations, at which time, by drawing back the bar by the fquare end, c, fig. 2. which is otherwife retained in its proper place by means of the featherfpring, the catch e, fig. 1. is released, and the door f of the efcutcheon is thrown open by the fpring, g.

When an alteration of the arrangement of the letters on which the fecret depends, is defired, the bar B must be held back by the square end c, while one or more of the outer circles are turned round till the letters chofen are uppermoft; the efcutcheon cannot afterwards be opened till that fame arrangement is again made, and fo on according to whatever fituation of the letters the owner may

choose :

choose: hence it is evident that which ever of the letters have been chosen must, at the time of opening the efcutcheon, be brought in one line to the upper furface of the rollers; and then the bar being drawn back, the door of the efcutcheon will be thrown open.

Fig. 1. reprefents the under or inner fide of the efcutcheon, and fig. 2, the upper or outer fide, and appears as when fixed over a lock, and covering the keyhole.

Nov. 24, 1784.

THE filver medal was voted to Mr. Taylor, of Petworth, for his improvement of Latch Locks, of which the following is an account, extracted from his letter on that fubject.

The latch, or spring bolt of door locks on the common conftruction (whether mortice,

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mortice, cafe, or rimmed locks) is very liable to be out of order, as foon as the oil is dried up between the tumbler and tail of the latch, from the erroneous manner in which the tumbler is made to act; and more especially, when the lower arm of the tumbler is engaged, for then the friction is very great, and the bolt very hard to be moved. To remedy these defects, I beg leave to fubmit to the judgement of the Society, a method I have lately thought of, and put in execution, of constructing, at a fmall expence, the tumbler and tail of the latch or fpring bolt, in fuch manner, that the lock may be conftantly used for many years, without any oil to thofe parts, and always move alike both ways, that is, by turning the knob or handle either to the right or left, and with lefs force of the hand in turning it.

The alteration which conftitutes the difference between this lock and thofe in common ufe is, that the tumbler is reverfed,

verfed, fo that the curved fide of the tumbler act against two ftubs fixed on the tail of the latch, and thrufts it easily back, whether the knob is turned to the right or left in opening the lock; behind the tail of the latch is alfo fixed a guide, having within it a groove, wherein runs a small friction-wheel, ferving to keep the latch in its direct fituation, and leffen its friction the arms of the tumbler are not fo long as they are generally made, because the latch or fpring bolt must move the easier by their being shorter,.

By the above conftruction, thofe parts of the tumbler and tail of the latch, that are in contact, move in a line, the nearest to the chord of a circle, whose radius is the arm of the tumbler, and confequently pass over the greatest space under the leaft angle poffible. The friction-wheel beforementioned, being placed on a ftub rifing from the tail of the latch, and in a line with the centre of the tumbler, and having the spring that pushes the latch or bolt L 4 forward