Engineering Wonders of the World
Volume I

380 ENGINEERING WONDERS OF THE WORLD. house, 100 feet above high water, was torn from its bracket during a severe storm and washed away, together with Extraordinary flagS^ag anj ladder lashed of Waves. to the SalleiT A fragment of the bell was afterwards found in a cleft of the rock, and may be seen to-day at Trinity House. It seems almost incredible that water should rise to the appal- ling height of 100 feet in volume sufficient to sweep away huge masses of metal. That they did so is beyond all doubt. Sir James Doug- lass, who for two years worked with his father in the construction of the granite tower, stated in 1892 that in heavy seas “ the primary wave flowed freely over the rock at a height of about 50 feet above its summit. There was very little break in the wave, except on the tower itself ; and there a rather lighter wave rose and reached the cavetto of the lantern gallery, where was produced a third and still lighter wave of heavy spray, which struck the lan- tern, and, rising far above it, drove a long way to leeward, sometimes nearly a third of a mile.” ; Fig. 20 is a sketch prepared from a diagram by Mr. W. T. Douglass, and gives a striking idea of the wild seas raging about the Bishop Rock, whose sugar-loaf formation doubtless aggravates the height of the waves in that stormy outpost. While hurricanes were in progress, the tower of 1851 vibrated so much that objects were shaken from shelves in the living rooms, prisms of the lighting apparatus were fractured, and, finally, some blocks of granite were split by the excessive strain. These alarming occurrences led in 1874 to the application of heavy iron bolts to the interior surface of the walls ; but despite this rein- forcement further evidences of damage ap- peared in 1881, among them being the break- ing away of pieces of granite weighing half a hundredweight each from the face of the The Tower badly- damaged. outer blocks. Consequently, for the third time, the Trinity House were called upon to legislate for the Bishop Rock Lighthouse. Acting on the advice of Sir James Douglass, they determined to case the tower with masonry dovetailed horizontally and verti- cally from foundation to ser- vice-room level, and to con- tinue th© tower upward for four additional stories, with a An External Casing required. new lantern whose focal plane would be Fig. 21.— BISHOP ROCK LIGHT- HOUSE. IMPROVED TOWER (Douglass, 1887). 146 feet above high water, and showing a light having a range of about 20 miles. The out- line of the im- proved tower, constructed un- der the super- intendence of Mr. W. T. Douglass, is given in Fig. 21. It was de- signed to pro- vide for the a dditional height of 36 feet, and to utilize to the utmost the width of foun- dation afforded by the rock. The granite blocks forming the casing and new stories ranged in weight from 2 tons to 3£ tons. They were carefully dressed and erected temporarily in the work- yard at St. Mary’s. To provide for the conveyance of material from that island to the rock a small twin- screw steamer was bought. This vessel, origin-