Engineering Wonders of the World
Volume I

372 ENGINEERING WONDERS OF THE WORLD. SEVERAL COURSES OF A LIGHTHOUSE FITTED TOGETHER AT THE QUARRY TO MAKE CERTAIN THAT THE STONES FIT ACCURATELY. built the tower solid in the lower part, made it of circular form above with a curved profile, and added an overhanging curved cornice to throw back the crests of waves. (See Fig. 3.) Although Smeaton’s tower was not free from defects, and may not have been altogether desirable for so exposed a situation, the general idea was correct, and virtually served as a model for the many larger and better lighthouses built during succeeding years. As an example, let us turn to the Bell Rock Lighthouse, built in 1806 by Bell Rock D -p. - , a , . , R. Stevenson. ±igs. 5 and 6 Lighthouse. show that Smeaton’s general profile and system of dovetailing have been followed, although th© latter structure em- bodies undoubted improvements. One \ of these is the height of 100 feet as compared with 68 feet, thus raising the lantern above the highest breaking and reflected storm waves ; another is the' greater thickness of the walls, obviating the vibration from which Smeaton’s tower suffered ; and a third is the adoption of lintel stones for the floors, so shaped as to dovetail into the outer walls, as represented in Fig. 7. The latter arrange- ment is much superior to that in the former Eddystone Lighthouse, where the floors were genuine arches exerting thrust against the outer walls. To counteract this force chains were embedded in the masonry (see Fig. 8), but the result could not possibly be so satis- factory as the form of construction adopted by Stevenson. Owing to the great mass of solid material near the base of the Bell Rock tower, the centre of gravity of that structure is low, a circumstance giving stability against failure by overturning. The same feature is