III.—The distribution of the magnetic field and return current round a submarine cable carrying alternating current.—Part 1

• Published in: Philosophical transactions of the Royal Society of London. Series A, Containing papers of a mathematical or physical character Containing papers of a mathematical or physical character, 1924, Vol.224 (618), p.95-140
• Main Author: Drysdale, Charles V.
• Format: Article
• Language: English
• ISSN: 0264-3952; 2053-9258
• DOI: 10.1098/rsta.1924.0003

Among the scientific problems to which the late war gave rise, one of the greatest fundamental and practical importance is the determination of the conditions of propagation of impulses or disturbances of every kind below and above the surface of the sea. As sea water is a medium of fairly high electrical conductivity, the propagation of electromagnetic waves, especially of high frequencies, is greatly affected by the absorption in the water and the distortion at the surface. In view of the applications to signalling, the guiding of ships over submarine cables, and the actuation of mechanisms, a knowledge of the distribution of the intensity and direction of the magnetic field produced by a submarine cable or loop is of the greatest practical importance, apart from its scientific interest. The investigations described in the present paper commenced in January, 1918, when the writer was called to the Admiralty Experimental Station at Parkeston Quay, Harwich, for the purpose of devising control mechanisms actuated by submarine cables. It was immediately obvious that absorption by the sea water might prove to be a serious factor in diminishing the intensity of the magnetic field, and that low frequencies would therefore be preferable. Calculations were therefore made concerning the propagation of electromagnetic waves in the sea, but as these applied only to plane waves in an infinite medium it was also decided to make a few direct measurements on the absorption of the field produced by a 300 by 200 yard loop which had been laid down at the mouth of Harwich harbour, the result being to show that absorption had no serious effect at frequencies of 30 to 20 ~ per second. This result was sufficient for the immediate purpose.