Engineering Wonders of the World
Volume I

THE MARCONI TOWERS, POLDHU, CORNWALL. 441 SECTIONAL PLAN OF TOWER, SHOWING METHOD OF ARCHED BRACING. A, Verticals; B, Inside Brace; C, Outside Brace; D, Distance Block, and E, Diagonal Tie-bolts. ously to be expected on a cliff 120 feet above sea-level, fully exposed to the Atlantic. Only those who have experienced Tremendous r , , one can realize what a genuine Al* Atlantic gale means, though some idea may be conveyed by the fact that on one occasion the Robinson anemometer at the station registered a wind velocity of 104 miles per hour. Allowing for the inherent inaccuracy of the instrument at this excessive speed, the velocity must have been at least 95 miles per hour, exerting a- pressure of about 30 lbs. per square foot. An empty metal-lined packing-case, some 3' 6" cube, and weighing nearly 3 cwt., was bowled across the ground like a football, ultimately smashing it- self against a stone wall. Any one attempting to cross the open had to do so on hands and knees. An iron weather-vane on the top of the Poldhu Hotel was bent 20° out of the perpendicular. Yet not a stick was stirred on either of the four towers. That serious damage was not done in the neighbour- hood on this occasion is due to the fact that everything built by man in the dis- trict is designed to withstand these violent gales. The principal materials of which the towers are composed are Baltic timber rough sawn into planks, such as may be readily obtained from any timber merchant; iron bolts, Details of , o . . the Towers, varying m size from £ men up to inches diameter ; mild steel plates ; and stranded steel wire, of which to form the stays. The construction is similar to that used for what is known as a “ Scotch derrick,” frequently employed as a support for temporary cranes on large buildings in course of erection. As will be noticed in the illustrations, however, the usual cross bracing is replaced by a zigzag system in order to obtain greater rigidity; and to avoid racking or distortion from the square form, long bolts pass through the vertical members diagonally. The total height of each of the structures is 275 feet from the ground, of which 215 feet is contributed by the tower, the remainder by the 60 feet mast fixed at the top. The width of each side is 21 feet at the ground and 9 feet at the crown, where is placed a platform 15 feet square to give room to manipulate the aerials, a matter which at the time of erection required some consideration, because a final form and size of aerial necessarily had to be decided on after comparison of experimental results, a course which involved the constant changing of aerials at all times of the day and night. The vertical members or corners are made up of planks 11* x 3", bolted together side by side in fours, so as to form a total section of 11" x 12", and so arranged that no two joints occur at Wire Cable n • Stays. the same point. Where out- side planks meet, the joint is further strength- ened by an iron plate thick. The trans- verse members or braces are each composed