As the weight of such lead roofing considerably exceeds that of the glass ridge-and-furrow covering, it was necessary at the point where it crosses the wide span of the main avenue to introduce some stronger roof-girders than those used elsewhere; of these there are two on either side of the transept, the inner one of which has also to sustain two of the large arched ribs with their superincumbent roofing, and its strength is therefore increased in proportion to the additional load placed upon it. The extra-strong roof-girders are six feet deep, or twice that of the others; but their general construction is similar, the diagonal ties forming a kind of latticework, and thus keeping up the same character. These, like all the roof-girders of large span, are constructed principally of wrought-iron. Those who visited the building during its erection, and were among the fortunate few who were enabled to ascend to the "lead-flat," must have been very much struck with the singular appearance presented by the great expanse of acres of glass stretching in long lines of "ridge-and-furrow" roofing on each side of the centre, while the eye, penetrating the transparent covering, became lost in endeavouring to follow the apparently intricate lines of the interior. Such a view might fairly be said to justify the title of "Crystal Palace," by which this building is so commonly known; and it would require no great stretch of imagination to believe that it had been reared by fairy hands, as a votive offering at the world's jubilee of labour. But we must descend again to the interior, to point out the arrangement of the offices for the staff of the Executive. The principal of these are naturally placed in the centre, on either side of the principal entrance, where they occupy in two storeys the space underneath the gallery, which is continued uninterrupted over them. The entrances at the end are also flanked by offices of less extent. The outer inclosure of these spaces is formed with glazed sashes, similar to those which are placed on the exterior of the building, and boarded partitions divide the interior. The rooms are arranged to be heated and lighted by gas when required, and ample means of ventilation are provided. The simplicity of the construction renders it very easy to extend or contract the accommodation much more readily than would be possible under ordinary circumstances.