With infinite difficulty a small corps of daring workmen and appliances of the simplest description, together with materials, were got out to the rock upon the first favourable day when there was a very low tide. An outer wall of bricks was built piecemeal, and the space within was filled with concrete. This stood, and so the engineer secured a level plinth upon which to place his tower. He selected an octagonal building, the angles of which touch the circumference of a circle 20 feet in diameter described on the rock. It was to be 50 feet in height, bringing the warning light about 40 feet above high-water. The beacon was to be a concrete monolithic structure at least for the greater part of its height, as the light was to be of the unattended class. Accordingly, the mould was formed by setting a cast-iron post, 18 inches in height, at each corner of the octagon, this support being anchored into the solid rock beneath. These posts contained grooves to admit sliding wooden uprights, which were to be firmly wedged, these joists being inclined to take the angle, or batter, proposed for the tower. Heavy transverse pieces of timber were laid between these posts, forming a capacious octagonal box, into which the concrete was poured. As the filling process behind the wooden wall advanced, angle pieces of steel were superimposed and bolted up. [Illustration: THE JUMENT LIGHT RECENTLY ERECTED OFF USHANT. This beacon was built with a legacy left by M. Potron, a distinguished French traveller, in the interests of humanity.] The security of the structure occupied the sole attention of the engineer. When work had to cease, and the boat put off with the workmen after a spell of toil, the engineer would watch the rising tide and the waves sweeping over his structure, until at last it disappeared from sight. As the tide fell he followed the receding waters just as eagerly, and gave a sigh of relief when he saw that the tower was still withstanding the blind forces of Nature. In the early stages an effort to protect the work, when the men had to retreat before the rising tide, was made by covering it with a heavy piece of sailcloth, lashed down and weighted in position with huge masses of pig-iron. This served its purpose for a time, but finally the sea got the upper hand, tore the canvas from its lashings, and carried it away, together with the whole of its weights. Then a wooden protective device was employed, and this likewise held out until a particularly unfriendly September gale smashed it to matchwood, as well as damaging the concrete slightly here and there.