1866.] 



the West Coast of Scotland. 



43 



coast, while the times of slack water are nearly the same throughout the 

 whole region in question. In a great part of this region the current, which 

 sets for six hours in one direction, has no distinct title to be considered 

 either a flood tide or an ebb tide. The consequence is, that to describe 

 the laws of the currents by reference to the time of high and low water, 

 introduces great and unnecessary complexity. The application to the 

 currents of the method first applied by Admiral Beechey to the tidal 

 stream of the English Channel and German Ocean (Phil. Trans. 1851, 

 p. 703) introduces at once order and simplicity, and makes that intelligible 

 which before was only a confused maze. 



In the following paper an attempt is made, from the materials to be 

 found in the charts of the Admiralty Survey of the west coast of Scotland, 

 now nearly completed, to obtain a first approximation to a tidal chart of 

 the west coast of Scotland. For this purpose I have, with the kind assis- 

 tance of Commander Evans, F.R.S., the first Naval Assistant to the 

 Hydrographer of the Navy, deduced from the charts all the information 

 to be there found as to the direction and times of change of the tidal 

 streams, as well as the times of high and low water. The latter are indi- 

 cated in the usual way by Roman numerals, v.hich, to avoid confusion, are 

 always within the land. The times of change and direction of the currents 

 are described by a particular symbol which I have found convenient for 

 the purpose, and which I will now describe. 



In the seas which we are considering, the stream at any point generally 

 flows for six hours in one direction and for six hours in the opposite direc- 

 tion. This may be conveniently indicated by the following symbol : — 



which indicates a stream flowing from XII. o'clock to VI. towards the east, 

 and from VI. to XII, towards the west. 



In this notation, for simplicity, the interval of the tide is considered as 

 12 hours instead, as it really is, about 12" 25°". The hours are expressed 

 in Greenwich mean time. 



The same symbol is adapted to the case of a stream flowing longer in one 

 direction than in the other. Thus in the Sound of Sanda the stream at full 

 and change may be indicated by 



V ^- j 



indicating that it flows seven hours towards the west and five hours to the 

 east. 



The velocity of the stream may be expressed by the length of the fi -ure, 

 or sometimes more conveniently by separate lines, the termxinations of which 



are well marked as | ], the length of the lines indicating either the 



velocity at the middle of the stream, or, if it is found more convenient, the 

 whole distance which a particle of water moves in one tide. 



E 2 



