Page:The museum, (Jackson, Marget Talbot, 1917).djvu/65

Rh hanging maps is not so apparent. In buying the stereopticon for the large lecture room it would perhaps be as well to provide a double-barrelled one, as it is certainly very convenient at times to have two pictures on the screen, side by side. Some museums may want to instal a reflectroscope by means of which it would be possible to throw upon the screen photographs or illustrations in books and other opaque material, in addition to the slides. There are several such machines on the market which are fairly satisfactory in a small room and with material which does not exceed 6x6 inches in size. Books are not as easily handled as the dealer usually represents them to be, and the strong focussing of light on the photograph or post card creates heat which is liable to burn it up if kept in too long.

Some museums have deemed it wise for the stereopticon to be in an adjoining room. In this case the end of the lens projects into the lecture room through a hole in the wall and all noise of the machine is shut off. In case this is done, some sort of a speaking tube has to be arranged so that the operator can get in touch with the lecturer, as a bell is not always sufficient to explain the lecturer's needs. Where two lecture rooms (a large one and a small one) are arranged side by side, some such system as this might permit