which show us, with great probability, the uses to which the keys were put, and it is to these that we must turn in any attempt to trace back the history of the mechanism from the commencement. The process is one, the merits and demerits of which have been too often discussed to need comment here. In the absence of direct archæological evidence we have no alternative but to avail ourselves of survivals as far as possible. The materials, however, in the case of locks are so abundant that it will not be necessary to tax our imagination unduly in order to fill in the links that are found wanting.

Of the bar, whether of wood or iron, used for fastening up the door on the inside, little need be said, nor are we at a loss for a commencement in the common door bolt. Figs. 2 and 3, Plate I., represent the inside view and section of a wooden bolt now in use on barns and outhouses at Gastein, in Austria, and like many of the ordinary appliances which in most countries are now made of metal, it is there constructed entirely of wood, and is such a bolt as might have been used in the most primitive state of society. It is intended to open from the outside, where the handle, consisting of a flat oblong piece of wood (fig. 3, a, Plate I.), communicates, by means of a neck of wood, with the bolt b on the inside, and when shoved home to fasten the door, the neck moves along a slit in the door shown by the dotted line, fig. 2, c c, Plate I. Such a bolt can of course be opened by any one whether from within or without, and it has the further insecurity of being liable to be forced open accidentally by anything that might catch the handle, there being no fastening within to keep it securely in its place when shut. The simplest contrivance for remedying this latter defect would be to insert a peg or pin into the bolt, which might be left hanging by a string fastened to a staple when the door is open, and when bolted, inserted vertically into a hole in the top of the bolt in front of the upright guide or staple through which the bolt slides, as represented in figs. 4 and 5, Plate I., and it could be got at from without through a hole in the door. By this means the bolt would be kept securely in its place when shut, but it would require two motions both in opening and shutting the door.

Anything calculated to save time in a process of such ordinary occurrence as the opening and shutting of a door would be speedily adopted, and it would soon be found that by fixing the pin vertically in a slide, so as to fall freely, and making the lower end smooth, so as to slide along the upper surface of the bolt as the latter was drawn back, it might easily be so contrived that when shut it should fall by its own weight into the hole in the bolt, as represented in figs. 6, 7, 8, Plate I.; in the former of which it is shown open, and in fig. 7, shut, with the pin down in the hole, so as to secure it from being drawn back until the pin is raised, which might be done from the outside by means of a hole in the door, through which the string might be made to pass, as shown in the section, fig. 8. By this contrivance the bolt would only require one motion to shut it securely, and it might also be placed in the inside; but to open it again two motions would be necessary as before.

Still, however, the fastening would be accessible to everyone, and in a condition of society in which property must always have been insecure, it would become a great desideratum to construct a bolt which could be drawn back only by the use of a key, which the owner might carry about with him, and thereby secure his goods and chattels whilst he himself was absent in the fields, or in the hunting grounds. So necessary a requirement of every day life must have forced itself upon the notice of the greater part of mankind, and it is not surprising, therefore, to find that this stage of the development of the lock forms the point of trifurcation of three separate branches of improvement. Two of these are of the nature of tumbler locks, and consist of apparatus for raising the pin or pins by which the bolt is secured when they fall into the holes provided for them on the upper surface of it. It was for this reason that they were termed tumblers, because they tumble into the holes when the lock is closed. The third branch led off in another direction.

In order that the mind may not wander from the lines of continuity whilst I treat each of these three branches separately, I shall class them as A, B, and C in the diagrams, at the same time allowing the numbers of the figures to run on continuously from this point of departure. By this means I shall be best able to show the ramifications into which this mechanism, like all similar contrivances to which these papers relate, separate as they increase in complexity.

The common door bolt (figs. 2 and 3, Plate I.) having continued to be available as an inside fastening, in addition to more complex contrivances for securing doors, has continued to be universally employed up to the present time, and may be compared in nature to those fossil species, which, having never become unsuited to their environment, have survived throughout successive geological periods, whilst the forms represented in figs. 4 to 8, Plate I., being makeshifts, have disappeared as soon as they were superseded, and thus they constitute the "missing links" of our developmental series.

The two great desiderata in the stage of the lock that we are now considering were security and rapidity, both of which must have forced themselves on the notice of the primeval householder each time he crossed the threshold of his door. I shall begin with branch A in which security only appears to have been aimed at, and then proceed to those in which security and rapidity were combined. The first idea which suggested itself was to put a bolt in a box, so that no one could get at it to lift the tumbler without a key especially adapted to enter the box and raise it, but as long as only one tumbler was used it must have been very easy to pick such a lock by raising the tumbler with any sharp-pointed instrument that might be introduced into the hole. By using two tumblers, it would be impossible to raise them both at once, except by a key constructed with projections or teeth to fit into notches or holes in the tumblers, which teeth must necessarily be at the same distance apart as the notches, and as the tumblers were hidden in the box, no one unacquainted with the contrivance could make a key to fit the lock, which by this means afforded to some extent the security that was requisite.

Scandinavia appears to have been the headquarters of this class of locks, or at any rate the part of the world in which they have chiefly survived at the present time; one of the simplest of which is represented in figs. 9A, 10A, and 11A, Plate I., from the Faroe Islands. e is the wooden block into which is cut a horizontal groove for the bolt a, and two vertical grooves in which the pins or tumblers, d d, play, and when the bolt is shut to, they fall of their own accord into the holes f f. The key, c, is passed horizontally into another groove cut for it in the block, above and parallel to the one for the bolt. Two notches are cut in the tumblers to enable the key to pass, and when pressed in horizontally as far as it will go, the teeth of the key, b b, coincide exactly with the notches in the tumblers, so that when the key is afterwards raised vertically, it raises the tumblers, by means of the notches, out of the holes, f f, on the upper surface of the bolt, and the bolt can then be drawn out by the hand. It will be seen that this lock requires as many motions as the bolt (figs. 6, 7, and 8, Plate I.). It requires only one motion to shut it, when the two tumblers fall into the holes and keep it fast, but to open it, it is necessary to use both hands, one to raise the key and the other to draw out the bolt. It may therefore be termed for