=The Alcoves.=--The alcoves behind the screens are in two stories, like the arcading, and are intended to contain a collection of the most necessary standard books on all important topics. The entrance from the floor of the Reading Room is through the central arch of the screen. One may pass through doors in the partitions from one alcove to another, on either floor; and by means of a winding staircase inside each of the piers one may go up or down, not only from story to story, but, on the one hand, into the basement below, and, on the other, to the space between the inner and the outer dome above. Altogether, the alcoves have a capacity, with their present shelving, of 130,000 volumes. The cases are of iron, and similar in a general way to those in the large stacks, to be described later; but they are built against the walls, according to the older method of library arrangement, and with very little attempt to combine them in a real stack system, properly so called. The upper shelves in the lower story are reached from a small iron gallery; in the second story a step-ladder must be used--the only instance in the whole building where a book-shelf cannot be reached by a person standing on the floor. [Illustration: PHILOSOPHY. BY BELA L. PRATT.] In front of each of the great piers of the Rotunda is an engaged column, so called because it is not quite clear of the mass behind it, which serves as the ultimate support of a statue placed between the arches upholding the dome. In height, base, and capital, it is the same as the pier with which it is connected, and, like it, is sheathed in Numidian marble, but not so dark in tone, since the burden resting on the column includes no part of the dome, and is therefore much lighter than that borne by the pier. The engaged columns, however, join with the piers to carry an elaborate entablature some seven feet in height, which, finding its way in and out of the alcoves from pier to pier, completely encompasses the room. The color of the entablature, which is entirely of stucco, is a cream or ivory white, like the dome, touched sparingly with gold. The mouldings, which are of the usual Greek patterns employed in Renaissance architecture, are very rich and heavy. The topmost member of the cornice is boldly projected upon a series of modillions, the soffits between being ornamented with rosetted coffers--gilt on a blue ground. The frieze is enriched with an arabesque of Renaissance ornament in relief, including antique urns and lamps; garlands enclosing tablets; and winged half-figures. The general design of the frieze, as of all such work in the Library, is by Mr. Casey as architect; the individual figures, however, were modelled by Mr. Weinert.