349 
1921-22.] The Invention of the Pilot Cable. 
“In 1921 this Prize (of 6000 francs) was awarded to M, Loth for various 
important devices having special applications in Navigation. In the ‘ Kapport 
de M. le Yice-amiral Fournier sur les creations scientifiques de M. W. A. Loth 
et leurs importantes et fecondes applications a la Marine’ {Comi)tes Rendus, t. 173, 
p. 1230) we read under the fifth section, on p. 1231, these words: — 
“ ‘ 5° Solution dll problmne de la conduite des navires a leur entree dans 
un port et, a leur sortie, en temps de brume et, en temps de guerre, pendant 
la nuit, les phares eteints, au moyen d’un cable guide. 
“ ‘ Ce cable elonge sur le fond de la mer est parcouru par un courant 
alternatif, de frequence musicale (600 a 1000 periodes par seconde). Ce 
courant cree dans I’espace environnant un champ magnetique variable^ 
special. La forme de ce champ varie avec la frequence. Ses lignes de 
force traversent les, surfaces de cadres fixes places a bord et au dessus des 
navires et disposes, d’apres la forme speciale du champ, de telle fa9on que 
tout batiment, sans autre moyen de se diriger, puisse connaitre a tout 
instant : 
“ ‘ 1“ La direction du cMde'; 
“ ‘ 2° Le nombre de degr^s d’inclinaison de sa route sur cette direction ; 
“ ‘ ?>^ Sa distance a ce guide et le cote ou il suit.’ ” 
In these sentences M. Loth is tacitly credited with the solution of a 
problem which was solved in essentially the same way^ by Mr C. A. 
Stevenson, F.R.S.E., twenty-nine years ago. The use of the pilot cable will 
be found described in a paper read by him before the Royal Society of 
Edinburgh on January 30, 1893, and published in that Society’s Proceed- 
ings, vol. XX, p. 25. In 1891 Mr Stevenson had already exhibited his 
apparatus at work to the Commissioners of the Northern Lighthouses ; 
in 1892 he took out a patent for the pilot cable ; and a few years later 
constructed a working model representing the French coast in the neigh- 
bourhood of Ushant, and showing how such a protecting cable could be 
used to warn ships off that dangerous shore. This model is still exhibited 
in the Royal Scottish Museum, Edinburgh. The following extract from 
the complete specification of Mr Stevenson’s patent of 1892 may be com- 
pared with the statement given above in the “ Rapport ” by Vice-Admiral 
Fournier. 
“ My invention consists of an entirely new method of warning vessels 
electrically of their position or of approach to a coast, shoal, mines, or any 
other danger. The apparatus consists of a submarine wire or wires laid down 
in the bed of the sea, river, or estuary, or out to any danger or anchorage or 
safe channel, through which intermittent currents are made to pass or the 
electrical state of which is made to alter by means of some form of electrical 
machine, generator, or battery. These currents or changes of electrical state 
are detected by a detector of such currents or of the change of magnetic 
influence or whatever it may be called, which detector may be on the ship or 
let down by rope or cable, or coiled round the hull of the vessel. Vfhenever 
