THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOUKNAL OF SCIENCE. 



[SIXTH SERIES.] 



JUL Y 1918. 



I. Scientific Signalling and Safety at Sea, 

 By Prof. John Jolt, M.A., D.Sc.', F.R.S., F.G.S.* 



[Plate I.] 



I. Approaching the Coast. 



THE most common-place and often one of the most urgent 

 of the problems which confront the sailor is the deter- 

 mination of his position upon near approach to the coast. 

 We may, indeed, say that the determination of latitude and 

 longitude at any time is solely in preparation for that stage 

 of the voyage when the ship draws near the land. The 

 special difficulties sometimes attending the solution of this 

 problem are known only to those who have endeavoured to 

 make a landfall or pick up a lightship in wild or thick 

 weather or in the calm obscurity of a fog. 



In our Admiralty Sailing Directions or Pilots we read that 

 there is no help for the sailor in a fog save unreliable fog- 

 signals and the use of the lead. The whole passage as 

 ordinarily given is intimately connected with our subject 

 and highly instructive. " Sound is conveyed in a verv 

 capricious way through the atmosphere. Apart from wind, 

 large areas of silence have been found in different directions 

 and at different distances from the fog-signal station, 

 in some instances even when in close proximity to it. 



* Communicated by the Author. Being the Tyndall Lectures 

 delivered at the Royal Institution, April 1918. 



Phil. Mag. S. 6. Vol. 36. No. 211. July 1918. B 



