Engineering Wonders of the World
Volume I

444 ENGINEERING WONDERS OF THE WORLD. to the actual results without conducting costly experiments. Two instances may be quoted to show the extreme rigidity of these structures. One tower in course of erection had just reached its full height, but was entirely with- out stays for the last 65 feet, which, being the top, was the slenderest portion. That evening was clear and fine and the glass steady, and the permanent stays being ready to attach on the morrow, the temporary ones usually used were for this once discarded. During the night there sprang up a gale, having a wind velocity of nearly 70 miles per hour, but it failed to make any impression on the tower. In the second instance, one of the towers developed a slight cork-screw twist owing to a small error in setting out, which, however, was not observed until the struc- ture had attained a height of about 50 feet. Although it was not detrimental to strength, it was decided to attempt a correction for the sake of appearances. A new hemp rope, four inches in circumference, was attached to each vertical, and carried at an acute angle to the side of the tower to a capstan on the ground. The four capstans were manned simultaneously, and a strain as nearly equal as possible put upon all four ropes. Just as the tower appeared to be straight, two of the ropes broke under the strain (the move- ment required was only about two inches), and the tower returned to its original form. The twisting strain on the tower at the moment of the ropes breaking may be safely estimated at not less than 16 tons at a radius of 10 feet and applied at a height of 50 feet above ground, and yet the only effect produced was a temporary movement of two inches at the point of application. It may be of some interest to give the results of the final plumbing tests applied after the towers had reached the full height and all the permanent stays had been fixed and made taut. The test was made in two Tests for Perpendicu= larity. ways—first, by means of a theodolite ; and secondly, by a heavy plumb-bob suspended down the centre. The latter test was carried out in each case in an almost absolute calm, with a line of fine piano wire on which was hung a weight of about 50 lbs., specially cast of lead and tested as to its accuracy. One tower showed a deviation at the base of one-eighth of an inch ; two a deviation of a quarter of an inch ; and the fourth (that with the twist) a deviation of five-eighths of an inch. It is hardly neces- sary to state that no attempt was made to improve on this result. The painting of the towers alone was a work of some magnitude. Each individual piece of timber or iron plate was given a good coat as soon as it was cut to size and before being fixed in position, Painting' and the whole of each tower tlle ^owers' received two more good coats after com- pletion. Each bolt-hole had a brush, previ- ously dipped in Stockholm tar, passed through it before inserting the bolt, which had also been dipped in the same preparation. All the unexposed ends of timbers were painted thoroughly with white lead, and every inch of steel wire was passed through a vat of paint before attachment. In May 1903 the station was visited by their Royal Highnesses the Prince and Prin- cess of Wales. His Royal Highness and most of the members of the party ascended to the top of one of the towers, from which a mag- nificent view of the grand coast-line of Mounts Bay is obtained. The towers were built on the assumption that- at the most five years would, see them superseded ; it is now seven years or more since their completion, and they are still as solid as ever, visible inland from the hills beyond Truro, 30 miles distant, and a landmark to those who go down to th© sea in ships.