=The Nave Aisles.=--We will first point out an unnoticed feature in the great piers at either end. Their inner faces as seen from the aisles have recesses or niches for the reception of monuments, and other recesses are generally found in the wall opposite. At the west of the aisles there are eight of these altogether, just behind the coupled columns. They are repeated in all the great piers leading to the dome, but although of sufficient height to permit of the introduction of life-sized effigies, still remain unoccupied. The coupled columns are repeated at the entrances to the chapels. At both ends the perspective is narrowed; at the west by the chapels, at the east by the breadth of the great piers. The windows stand in recesses which are segments of circles. Their sides are made to represent piers with concave surfaces. These latter carry an entablature from which spring the round window arches. Festoons run below the actual windows, the concave side piers have panels, and the round arches above diamond-shaped patterns. There are only three windows on either side--the chapels taking the place of a fourth--and the depth of their recesses points out the thickness of the walls. Between each recess are Composite pilasters in couples, with others opposite against the piers. These correspond with the lesser pilasters of the arcading, and from them spring transverse arches, as in the great central aisle. The vaulting, owing to the severies being nearly square, is regular; in other respects similar to that already described. The height is much less than that of the greater aisle, reaching only to the first stage of the latter. =The West Chapels.=--They may best be described as squares of 26 feet, with apses or tribunes at either end which increase the length to 55 feet. They suffer sadly from want of light, the one window in each being altogether insufficient; but Wren had to do what he could. He panelled them with oak, and made them of the same height as the aisles, with vaulting of his favourite kind, drawn out to meet the windows. The North Chapel is called the Morning Chapel, from its original use for morning prayer on weekdays. The mosaic above the altar is in imitation of a fresco by Raphael. That at the west end, by Salviati, is in memory of William Hale Hale, a voluminous writer and editor of the "Domesday of St. Paul's," who was a Residentiary, Archdeacon of London and Master of the Charterhouse. He died in 1870. The stained-glass window is in memory of the metaphysician, Henry Longueville Mansell, Dean of the Cathedral, who died suddenly, after a rule of three years, in 1871. It is by Hardman, and represents the Risen Christ and St. Thomas. [Illustration: THE GEOMETRICAL STAIRCASE.]