the 13th frame back will contain the cards of all books one day overdue, the 14th of those two days overdue, and so on. The detection of overdues by this means is easy and certain, and a check can be kept upon the books liable to be fined. The counter space required is very large, and this no doubt has been the chief reason of its non-adoption by other libraries.
The indicators used for simply showing the public whether a book is in or not, depend upon some system of card charging or book-keeping for recording the issue. One of the earliest of these, which is still in use at the Birmingham central library, is the "Morgan" Indicator. It has lately been improved and superseded by the "Simplex," manufactured by the same maker, and shown in Fig. 28. It consists of a frame in which numbered diagonal shelves are placed, the numbers showing when the book is in, and are hidden when the book is out. The method of work is for the borrower, or assistant, to enter the number or name of the book required upon a coloured slip of paper. This is placed in the frame, and covers the number of the book from public view. Different coloured slips are used for different periods of time, and so the overdues are seen at a glance. The borrower's ticket. may have coloured ends, and be placed over the number instead of the coloured issue slips.
The "Chivers'" Library Indicator, shown in Figs. 29 and 30, differs materially from the others described in this chapter. An indicator for a thousand numbers consists of four movable blocks, enclosed in
