This invention consists in the use of a series of slides provided with teeth or racks, and arranged with a bifurcated bolt into the parts of which the ends of the slides work or pass, and a series of bits attachod to separate arbors placed one within the other, and operated by means of keys or knob$. In our illustrations, Fig. 1 is a horizontal section of the lock, and Fig. 2 a transverse one, and from them and thefollowing description the lock will be understood. A represents the case of the lock which is of metal and of the usual quadilateral form. The bolt is formed of two bars, B, being connected at their inner ends by the bar, C, that is connected by a rod, D, to a crank pulley, E, on the end of the shaft of the knob, F. By this means the bars, B, are moved in and out ---------------------------------------------------------- S by turning the knob, F, The bars, B, work, oue at the upper end and the other at the lower end of the case, A, and between the top and bottom plates of the case and longitudinal plates, a a, the inner ends of a-being connected to a bar, b. G. represents a serias of slides which are placed one over the other and fitted together, each slide having a longitudinal recess, c, made in it, at one side of its center and a projection, d, at the opposite side, the ledge or projection of one side fitting into the corresponding recess of its adjoining one. The ends of the slides, G, pass through openings in the plates, a; corresponding openings being made in the bars, B. The slides, G, are made of such a length that when adjusted centrally with the case, their ends will be flush with the outer edges of the first mentioned opening, and springs, G', are fitted in the case to keep the slides in their proper place. To the front side of each slide, G, a series of teeth, ", are attached, and in addition to these there are some yielding or elastic teeth, "', placed one at each end of the teeth, I., giving or yielding only in one direction, and being . perfectly rigid in the other. represents a series of bits which are attached to bosses, i, each of these being attached to arbors, jki m, fitted one within the other, each arbor being allowed to work independently of the others. Each arbor passes through the outer plate of the lock, :md each is provided at its outer end with a knob or thumb wheel, n. The bits, H, are so placed that one will be opposite each slide, G, and the bits are placed at such a distance from the teeth, ", of the slides, that the bits will gear into them, and move the slides as the bits are turned. The bars, B, when pushed outward from the case, A, are retained in that state by the slides, G, which are moved promiscuously, so that their ends will project into the openings in B, some of the slides fitting into one bar and some into the other, and in order to shut the bars back into the case, A, the slides, G, must all be so moved that their ends will be flush with the outer edges of the openings in the plates, a a. This is effected by having a mark, g, on each knob or wheel, n, coinciding with the position of its bit, A, and then when the lock is locked, the person must note the movement he gives each slide by counting the turns of the knob or wheel, n, through which it was moved, or an index plate may be attacheq to the outer plate of the lock in order that the position of each slide may be noted by the person who locks the lock. This being done, the same person of course can move the slides in proper positions, so as to liberate the bars, and therefore allow them to be moved back by turning the knob, F. The elastic teeth, "', arc to prevent the bits, H, being stopped, when the slides have been moved the full extent of their movement in one direction, the teeth, "', yielding to the action of the bits. When, however, the bits act upon the teeth in the opposite direction, that is, the direction in which the slides can move, the teeth, 1/, will not yield or give, and the slides will be moved, the teeth, "', acting 'in the latter case as stationary teeth. By means of the yielding cogs the positions of the slides are prevented from being discovered by being tampered with, the bits being allowed to turn completely round any number of times. ' One or more of the slides, G, may be used, and the lock therefore made as complex as desired, and placed beyond the reach of burglars. This lock is the invention of Mr. Joseph A, Bradeu, of La Grange, Ga., to whom a patent was granted June 8, 1858, and from whom any further information can be obtained.