=149. Metal Bookcases with Absolute Shelf Adjustments.=--The best and most used English variety of metal bookcase with absolute shelf adjustment is that which has been installed in the public libraries of Worcester, Shoreditch, Huddersfield, Lambeth, Perth, the Patent Office Library, London, Islington and elsewhere. It consists, as shown in Figs. 31, 34 and 35, of strong steel uprights, in which are formed continuous grooves, which carry and support shelf brackets designed to grip at any point by automatic means. These brackets will slide up and down the uprights to any point, while a small controlling lever is depressed, but the moment this is released the bracket will become firmly fixed in place, and will remain there till again moved, whatever weight may be placed upon the shelf which it supports. These brackets can be pushed up without touching the controlling lever, and will always grip at the point where they are left. To push them down, the controlling arm must be depressed as already described. The shelves for this type of case may be either metal or wood, but probably good oak shelves will be found as satisfactory as any. Standard cases made in the dimensions given in Section 145 are usually divided down the middle, at the back of each set of shelves, by means of a wire-work grill. This does not obstruct oversight, light or air, yet serves to prevent books on one face of the standard from being accidentally or otherwise transferred to the opposite face. There are points of safety, convenience and adjustability about metal bookcases which make them preferable to all other forms. [Illustration: FIG. 34.--Details of Lambert’s Adjustable Metal Shelving (Section 149).] =150.= A special form of this type of metal bookcase has been designed for book-storage in small spaces, and as applied to the India Office Library, London, and Bodleian Library, Oxford, has been found convenient and economical. The same shelf adjustment is used, but the presses instead of resting on the floor are swung from iron girders, so as to slide easily whenever wanted. These presses are swung closely side by side and drawn out, one at a time, as required. A somewhat similar plan for increasing the storage capacity was introduced into the British Museum many years ago, the chief difference being that the sliding presses go face to face with the existing standards, one here and there, instead of in solid rows as at the India Office. [Illustration: FIG. 35.--Metal Shelving, Patent Office Library, London (Section 149).] =151.= It is not proposed to describe every variety of iron or metal bookcase which has been introduced, such as the Library Bureau, Smith, Lawrence, Cotgreave, etc., and it will be sufficient to mention that in Britain, Germany and America there are several interesting forms used.