Behind the screen is a blackboard which can be used when the stereopticon is not needed. In addition, on both sides are racks upon which maps can be hung and raised or lowered by means of a very simple device. They are so hung that several maps or charts can be arranged, one above the other, and yet so that they can be exhibited with a minimum of effort on the part of the lecturer. Mechanical devices of this sort are a nuisance when overdone. The late Dr. Meyer of Dresden was one of the first to introduce a large number of such systems into his museum and the student will readily perceive which of them are more ingenious than practical. [See F. A. Bather, Many Inventions, Museums Journal, vol. IV, page 202, and Dr. A. B. Meyer, III Bericht über einige neue Einrichtungen in Dresden, 1903.]
Common sense is a prime requisite for any one connected with a museum. It must be possible to tell the difference between a device which will be expensive to instal and not very satisfactory after it is installed, and one which is absolutely essential to the working of the museum. In the case mentioned, the presence underneath the table of the switches which control the curtains and the lights, is excellent. The advisability of having a disappearing blackboard and arrangements for
