becomes more difficult. A system used in some places has certain advantages. A slot in the wall at a convenient hanging level is arranged. This slot is composed of two metal bars or two angle-irons let into the wall in such a way that one side is flush with the wall and they come together leaving a slot about ½ inch wide. Metal hooks are provided with a bar on the back. These hooks when turned can be pushed through the slot and when in place hold firmly against the metal edge of the angle-iron. With this system it is possible to hang the pictures very close against the wall and then there remains only the slot, which makes a somewhat disagreeable line around the wall. This same system, however, when used at the height of the ordinary moulding is not objectionable. In some museums where the walls are plastered, a wooden board about 3 inches wide has been let into the wall and painted the same color as the plaster. In this way pictures can be put up with nails or screws as desired, which is obviously an advantage, especially where collections have to be changed very frequently, when much time is saved.
In hanging pictures from mouldings, there are several processes which can be used. One frequently seen in European museums consists of using an iron about 1½ inches wide and per-
