EYE OF THE SUBMARINE

Nelson Evening Mail, 30 May 1916, Page 2

EYE OF THE SUBMARINE

A submarine T>oat sight-tube was invented as far back as-' 1854, byi Marie Davy, and 50 years later such lubes had begun to take practical shape. The periscope is the eye of the submarine, and in principle it is simple; in practice, it is <a very complicated piece of apparatus. Its details are quite secret, and it is probable that each navy has its own particular type of instrument. .Essentially (says the Marine Engineer and Naval Architect) it consists of a tube having, at its upper end, projecting through the surface, a right-angled reflecting prism, through which an image of a comparatively small portion of the sea is reflected through a similar prism at the lower end of the tube into an eye-piece, conveniently placed for the operator, who always stands facing forward. To obtain, a view of any part of the horizon, the tube can. be turned round- in any direction in azimuth. The tube is moderately large, requiring an electric motor to turn It rapidly. * With a periscope, such as described, if an image of a ship right forward is erect, that of a ship right aft will be inverted. That would' be most confusing to the commander, -and to obviate it, another prism is introduced to erect the image. This —the erecting prism—has to be rotated : at twice the rate of the main tube, in I order to obtain a constantly erect image. The eyepiece is arranged so that the operator gets a true perspective view of the field with slight magnification, and has an angle of vision of 50 degrees in a horizontal plane. An aeroplane directly overhead cannot be seen through the periscope. 'Considerable practice is required to ena'ble the instrument to be used' effectively. The periscope is not required for navigating when submerged deeply; in fact, it would- be useless., as it is impracticable to see half the length of the boat in ordinary sea water. Two periscopes are sometimes fitted in large craft, one for the, use of the captain, and) one for an observer, who is continually sweeping the horizon. __ The horizon, with the periscope four feet out oi the water, is barely two and a half miles distant.