The building, says an accurate authority,[29] had hitherto been carried up solid as high as there was any reason to imagine it would be subjected to the heavy rush of the sea; that is, to 35 feet 4 inches above its base, and 27 feet above the top of the rock, on the common spring-tide high-water mark. At this elevation it was reduced to 16 feet 8 inches diameter; and it was needful to make the best use of this space, and economize it to the utmost advantage consistent with the one primary and indispensable condition of _strength_. The rooms were built with a diameter of 12 feet 4 inches, having for the walls a thickness of 2 feet 2 inches. These walls were made of single blocks, and so shaped that a complete circle was formed by sixteen pieces, which were cramped together with iron, and also secured to the lower courses by marble plugs as before. To prevent any humidity penetrating through the vertical joints, flat stones were introduced into each, in such a manner as to be lodged partly in one stone and partly in another. With all these ingenious precautions, the twenty-eighth course was completely set on the 30th of September. [29] “Smeaton and Lighthouses” (edit. 1844), pp. 57, 58. This, and the next course, received the vaulted floor, which formed at once the _ceiling_ of the store-room, and the _floor_ of the upper store-room. For additional security, therefore, a groove was cut round the upper surface of the course, in which was lodged a massive chain of iron. Upon this chain, in the groove, melted lead was poured, until the cavity was filled up. The next course was laid and completed in a similar manner; and by the 10th of October Smeaton had nearly perfected his arrangements for establishing a light and light-keepers at the Eddystone, when his hopes were suddenly stricken by a prohibition from the Trinity House, based upon legal difficulties. But this being at last removed, the work was recommenced for the next and last season on the 5th of July. On the 21st, the second floor was finished; on the 29th, the fortieth course was laid, and the third floor finished. [Illustration: SMEATON’S LIGHTHOUSE AT THE EDDYSTONE.] On the 17th of August 1759, the main column of the lighthouse was completed. Forty-six courses of masonry had been laid, and the graceful structure raised to its specified height of seventy feet. The last work done, very appropriately, was the engraving of the words “Laus Deo” (Praise be to God!) on the last stone set over the lantern. At an earlier date, Smeaton, with devout humility, had inscribed on the course beneath the ceiling of the upper store-room, “Except the Lord build the house, they labour in vain that build it.” The iron-work of the balcony and the lantern were next erected, and the whole was surmounted by a gilt ball. The internal arrangements of the lighthouse were as follow:— First, the store-room, with a doorway, but no windows. Second, the upper store-room.