In the first designs for the Bell Rock Light-house, the writer had modelled a cofferdam, five feet in height, intended to have been erected of cast-iron, round the site of the building, that the work in its early stages might be continued for a longer period, both during the ebb and flood tides. The experience of last season’s work, however, shewed that the erection of the proposed cofferdam would have been attended with considerable difficulty; and, to have rendered such an apparatus equally useful during ebb-tide as flood-tide, would have required the pumping of water by machinery more complicated and powerful than the situation of the Bell Rock would have admitted. [Sidenote: Pumps.] This idea was therefore laid aside, and two Pumps, of a simple construction, were prepared, for clearing the foundation-pit of water. They measured about twelve feet in length, and were of a square form, both externally and internally, having each a void of ten inches. They were made of fir timber, three inches in thickness, strongly jointed, and put together with white-lead paint, having also a number of cross bars and bolts of iron, to strengthen them for withstanding the atmospheric pressure upon so considerable a surface. These pumps were furnished with a wooden spear or rod, having a cross head or handle at one end, and a leathern valve attached to the other. This valve was of a very simple construction; it collapsed when plunged into the water, and was inflated by the return draught delivering a quantity of water equal to the cubical contents of the void or chamber of the pump. [Sidenote: Winch-machines.] There were four Crabs or Winch-machines prepared for working the different purchases required in the various departments of the work, as, for example, in lifting the stones from the praam-boats, as represented in Plate XI. Another of these machines was fixed on the temporary wooden bridge of communication, erected between the Beacon-house and Light-house, as will be seen in Plate IX. Other two of these machines are likewise represented for raising the stones from stage to stage upon the building, as will be more particularly described in the letter-press description of this Plate. These machines were made wholly of iron, excepting the bushes for the gudgeons working in, which were of bell-metal. They were calculated to work with what is called _double and single purchases_, according to the weight of the stones to be lifted. They were very powerful in their operation: the winch or barrel being twelve inches in diameter, gave the single purchase a power of about fifteen to one, and the double purchase about sixty to one. These machines were calculated to work with five tons. The weight of the largest size was altogether about 10 cwt., so that they were not easily shifted by the impulse of the sea, when batted to the rock, as represented in Plate XI. _Building Materials._ [Sidenote: Stone.]