54

CONSTRUCTION OF TIIE BUILDING.

Their strength;

Their attachmentto connecting-pieces.

The connecting-pieces ;

'Flie attachment tothem oi’ girders

nection aud attachment of the necessary girders, which serve at once to supportthe galleries and roof, and to tie the various compartments of the building intoone vast network. The columns are made hollow, in order to convey thewater from the roof of the building; and the thickness of the metal of which theyare composed varies, according to the weight each column is intended to support,from | of an inch to li inch. The square faces already mentioned add, however,considerably to the sectional area of the metal, upon the amount of which thestrength of the column in a great measure depends.

The extraordinary strength to resist compression in the direction of its length,which the cylindrical form conveys to any material, was illustrated by ProfessorCowper, in a lecture delivered by him in the building to the members of theSociety of Arts. In a series of experiments with a common quill, and even witha straw, Professor Cowper demonstrated the great force required to crush suchslight objects, and, arguing from their comparative scale, illustrated satisfactorilythe great strength of the columns in the building.

Beneath the capital, which surrounds the upper part of the column, are con-cealed projections similar to those at the bottom of the column. These projectionsserve to attach to the columns what have been technically designated as con-necting-pieces. The peculiar office of the connecting-pieces is to afford, by asmall and consequently easily modified casting, the means of securely retaining,and connecting in all directions, the various girders throughout the building.

In fig. 4, we have endeavoured to exhibit the peculiar formation of thoseportions of the connecting-pieces, which serve to effect the end desired. Theprojections, or, as they are technically termed, “ snugs,” are cast upon the upperand lower portions of the connecting-pieces, and act partly as brackets and partlyas hooks, clutching over, supporting, and retaining, projections cast upon the endsof the standards of the girders. In order to retain the girders in a verticalposition, and to prevent any lateral movement, the bottom face of that portion ofthe girder which rests upon the corresponding projection of the connecting-piece,is formed with what is called a tenon, which drops into a mortice-hole (A, fig. 4),cast in the face of the projection of the connecting-piece with which it comes incontact. The top face of the portion of the girder, over which the hook cast upon

Fisr. 4.