SYDNEY PHENOMENON.

Manawatu Standard, Volume LI, Issue 72, 24 February 1931, Page 5

SYDNEY PHENOMENON.

ENGINEERS EXPLAIN,

The harbour bridge, now rapidly nearing completion, has a * ghost (states a Sydney correspondent). At regular intervals eerie wails are heard, but unfortunately for those who have a leaning to the supernatural, the engineers have a simple explanation. The uncanny sounds were first heard on the approach spans. They began faintly, then rose in volume, and then died away. They were first attributed to'the siren of a vessel passing beneath the arch, but the persistence of the sounds soon attracted more minute attention. Engineers were informed that strange noises , had been heard. They endeavoured to find a solution of the phenomenon. It was not easy. Several -theories were advanced and as quickly rejected. It wa3 suggested that the rivfetting machines were reacting fin certain members, causing them to . take up the vibration in sympathy, in the same manner as a tuning fork. This was soon discounted, for the sounds came strongly even when there were no rivetters at work. It was then suggested that gusts 'of wind were responsible. On the roadway section there are several vertical pipes for drainage purposes, and it was thought that, under the influence of the wind, they were acting.as the pipes for some huge organ. The occurrence of the sound on a perfectly still day exploded that theory. Now a very simple solution of the mystery has been found. It has been observed that the wailing has been heard only on days during which the temperature has varied greatly. On a cloudy day, broken by short periods of strong sunlight, the wnils are particularly noticeable. On such days there is considerable movement at the expansion joints of each steel truss. Due to the weight of steel bearing on the plates on which each truss slides, the friction is considerable. Movement then takes place in a series of forward and backward jerks. This irregular movement sets up vibrations in the members constituting the framework of each truss, which acts as an enormous tuning fork.