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.