Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

The force exerted by waves is well exemplified by what occurred during a storm at Peterhead some years ago, when blocks weighing 41 tons apiece were displaced at a level of 37 feet below low water, spring tides, the rise of the latter being 11 feet. On the same occasion a section of blockwork, weighing 3,300 tons, was shifted bodily two inches without dislocation. To move this mass, an energy equal to 2 tons per square foot must have been exerted simultaneously over the affected area. Something similar happened at Colombo during the construction of a break- water there, a length of wall at the outer end, 150 feet by 28 feet wide, founded at a depth of 20 feet below low water, being shifted inward as much as 15 inches, necessitating the resetting of this portion of the work. At the Tyne north pier works much damage occurred for several winters in succession from the same cause, resulting in the reconstruction of an outer section 1,500 feet in length. Depth to which wave action extends. It should be added, however, that wave disturbance occurs at considerably greater depths than those at which existing sea works arc founded. For example, Sir James Douglass, the well-known lighthouse engineer, recorded the fact that coarse sand was found on the gallery (120 feet above water level) of the Bishop Rock Lighthouse, off Scilly, where the depth of water is about 150 feet. Seeing that there is nowhere else that the sand could have come from, it follows that the material must have been washed up from the sea bottom and hurled into the air, a total height, from sea bed to gallery, of 270 feet. o OC