Upon the block thus prepared was set the central stone of the next course, having a similar hole in the middle, so as to receive the upper portion of the marble plug. Hence it is clear that no force or pressure of the sea, acting horizontally on any one of these central stones, could move it from its position, unless it were able to cut in two the marble plug; and to prevent the upper stone from being lifted, in case its mortar was destroyed, it was fixed down by four trenails. The blocks surrounding the central were dove-tailed together as before; and thus one course rose above another without any interruption, except from the occasional inrush of the waves or violence of the weather. [Sidenote: Smeaton's industry.] In his superintendence of the difficult and laborious work, Smeaton's activity and perseverance were unwearied. As soon as it had been so far accomplished as to present the appearance of a level platform, he could not deny himself the pleasure of a promenade upon it; but making a false step, and being unable to recover himself, he fell over the brink of the masonry, and among the rocks on the west side. As it was low water at the time, he received no serious injury. He dislocated his thumb, however, and as medical assistance was not available, he set it himself,--afterwards returning to his work. The incident is characteristic of the firmness and resolution which Smeaton exhibited throughout his busy career. [Sidenote: Building the light tower.] The ninth course was laid on the 30th of September, and concluded the operations for the year. On the 12th of May 1758, Smeaton and his "merry men" returned to the lonely wave-washed rock, and were delighted to find their work intact. The cement seemed to have become as hard as the stone itself, from which, indeed, it was scarcely distinguishable. Lusty arms and willing hearts made rapid progress; and by September, the twenty-fourth course was reached and laid. It completed the "solid" part of the building, and was designed to form the floor of the store-room; so that Smeaton had good reason to be satisfied with the progress made. But he knew how great an advantage it would be to exhibit a light in the coming winter; and therefore he resolved on completing the storeroom, if within the range of the possible, and planting a light above it.