In order to determine the level of the top of the base-pieces, boning-sticks were placed in the lines of the columns, and when the base-piece had been approximately fixed, a piece of wood was placed on it edgeways, the top of which was to range with the top of the boning-sticks. This was easily arranged by looking along them; and the workmen drove down the base-piece with a wooden mallet till the desired level was obtained.

From what has been previously stated, it may be gathered that the base-pieces had to be fixed truly upright in one direction, but slightly inclined in the other; and to effect this a plumb-rule was made, on which the deviation from the perpendicular line was marked; and this, when applied to those faces of the base-pieces which were to incline, served to show when the proper inclination was arrived at, whilst an ordinary plumb-rule applied to the other upright faces tested their vertical position.

The first column was raised on the ground on the 26th of September, but little more than two months after the tender had been accepted. In the meantime, many of the different castings had already arrived on the ground, and a considerable advance had been made in the carpenter's work for the gutters and other parts. The semi-circular ribs for the transept roof were also being put together, and stacked in such a manner as not to stand in the way of the other works.

VIEW OF CRANE AND PROVING-PRESS.

We may mention here that every casting, as it came on to the ground, was weighed and registered, and every girder proved, as already described; in doing which considerable assistance was derived from one of Mr. Henderson's patent Derrick cranes, which was erected near the proving-apparatus. By its means a girder was raised from the waggon in which it arrived, placed on the weighing-machine, weighed, removed to the proving-press, tested, raised again, and deposited on the ground in a stack, in less than four minutes.

(Fig. 1.)(Fig. 2.)(Fig. 3.)
HENDERSON'S DERRICK CRANE.PART OF HENDERSON'S DERRICK CRANE.PART OF HENDERSON'S DERRICK CRANE.

BRIEF description of this useful engine may not be out of place here. It consists of an upright mast (E), steadied when the crane is in use by two sloping stays (F F). These stays are fixed into horizontal timbers (G) on the ground, connected with the foundation-plate (H) on which the mast turns. At the foot of the mast is fixed a combination of wheels and working handles for raising the weight, technically called a crab. A beam (A) working at the bottom in a socket (B, Fig. 3) fixed to the foot of the mast, but hanging out from it in a sloping direction, is called the DERRICK, and forms the principal peculiarity of the crane, as it can be raised more to the upright line, or lowered to slope more outwards, as may be desired, by means of the chain (C). The advantage of this is obvious; for a weight may thus be raised from or deposited at any point within a circle of a certain radius, depending on the length of the derrick; whereas, in an ordinary crane, the weight can only be placed at points upon the circumference of that circle. The whole engine revolves on a pivot (H, Fig. 2) at the foot of the mast. Cranes of this description are made varying in power from one to forty tons, and with derricks ranging from twenty to sixty feet radius.