The Submarine Torpedo Boat
Its Characteristics And Modern Development

DESIGN OF THE SUBMARINE TORPEDO BOAT 95 the measurement of a very small angle and an assumed dimension for a base line. So far however, variations of these two systems are the best means at our disposal. The periscopes should have a field of vision of as near 45° as possible, compatible with proper illumination when showing objects at their true distances. All lenses and prisms must be free from imperfections and from spherical and chromatic aberration. The magnetic eyepieces should have a power of about 40, and a field as near 15° as possible. The binocular type should be preferred owing to the lesser degree of eye strain it affords, and soft rubber guards should be fitted. It is essential that these instruments be designed so as to allow all lenses and prisms to be accessible for cleaning. Arrangements must also be made for circulating dry air through each instrument and for hermetically sealing them after drying. Signalling and Interior Communication The advance in signalling devices and interior com- munications has kept pace with the rapid improvement made in other lines of .equipment for submarines. For surface navigation they consist of practically the same methods used on any other vessel, signalling being done by wireless communications, sirens, flag and shape in the day, and by wireless, sound and light signals at night. Port- able search-lights are also fitted on the bridge. It is only within the last five years however, that any means of signalling under water has been perfected. Now all boats are fitted with submarine bells and receiving and sending apparatus. It has been found that sound waves are transmitted under water nearly four times as