The next proceeding was to excavate the holes for the concrete, on which the base-pieces were to stand. To do this, the stakes marking the centres of the columns had to be removed, and it was therefore necessary to adopt some method of finding those centres again with precision. For this purpose a large carpenter's square, as it is called, was made. This instrument forms a right-angled triangle, and in this instance was used in the following manner:--The centre of its longest side, or hypothenuse, was marked by a line, which, if continued, would pass through the right angle of the triangle, and at an equal distance along each of the other sides of the triangle from the right angle an upright saw-cut or notch was made. The square was then placed horizontally, so that the line marked on the hypothenuse coincided with that of the centres of a row of columns, and so that the right-angled corner of the square touched the nail marking the exact site of a column. Two small stakes were then driven under the notches in the short arms of the square, and nails were driven into them through the notches. It will be seen that by these means the site of the first stake could easily be again ascertained after its removal. The holes for the concrete were then dug of an oval form and of the various sizes and depths required, and the concrete filled in to the proper height. The gravel used for the concrete was raised in a pit at one end of the ground. Next to the setting out of the positions of the columns, perhaps the operation of fixing the base-pieces was that in which the greatest accuracy was required; for as there were in some parts three storeys of columns to be fixed over them, any inaccuracy as to their level or position would be very much increased at the top of the building. To fix the base-pieces over the centres that had been determined for the columns, another carpenter's square was made use of, like that already described, but having the right-angled corner cut out to the form of the section of a column. This square being placed with the notches in its short sides over the two stakes already described, the upright portion of the base-piece was fitted into the notch at the angle; and as the reader will at once see, if he has followed us in the description of the various processes, its correct position was thus exactly found. 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.