with less plant than ordinarily required.  For engineering work, such as sea walls, the hexagonal slabs, made of greater thickness than those employed for ordinary walling, will answer admirably, especially if the grooves be made proportionately larger.  By the use of these slabs the work may be built up with great rapidity.  For small domestic work, such as the dwellings of artisans, these slabs; which are of such a form as to render them easy of transport, may be supplied to the workmen themselves in order that they may erect their own dwellings, as, on account of the simplicity of this system and the absence of need of plant, any intelligent mechanic can do the work.

Any arrangement of independent scaffolding may be employed for this system, but that invented specially for the purpose by Mr. Frank West, as shown in Fig. 26 of our engravings, is to be preferred.  It not only supplies the necessary scaffold, but also the necessary arrangements for hoisting the slabs, as well as for raising the liquid concrete and depositing it behind the slabs.  It is really an independent scaffold, and may be used wherever a light tramway of contractor’s rails can be laid, which in crowded thoroughfares would of necessity be upon a staging erected over the footway.  The under frame is carried upon two bogie frames running upon the contractor’s rail, by which means it is enabled to turn sharp curves, a guide plate inside the inner rail being provided at the curves for this purpose.  The scaffold itself consists of a climbing platform made to travel up or down by means of four posts which have racks attached to their faces, and which are fixed to the under frame and securely braced to resist racking strains.  A worm gearing, actuated by a wheel on the upper side of the scaffold, causes the scaffold to ascend or descend.  A railgrip, made to act at the curves as well as on the straight portions of the rail by being attached to a radial arm fixed to the under frame, assists the stability of the scaffold where required, but the gauge of the rails is altered to render the scaffold more or less stable according to its height.  Combined with the same machine, and traveling up and down one of the same posts used for the scaffold, is an improved crane.  Its action depends upon the proposition in geometry that if the length of the base of a triangle be altered, its angles, and therefore its altitude, are altered.  A portion of the vertical post up and down which the crane climbs forms the base of a triangle, and a portion of the jib, together with the stay, forms the remaining two sides.  Hence, by causing the foot of one or the other to travel upward, by means of the worm gearing, the upper end of the jib is either elevated or depressed.