468 



WHAT. IS THE TIDE OF THE OBEX ATLANTIC? 



say when the idea ofderivingtid.es from this southern ocean arose. 

 Lieut. J. Cook, reporting tidal observations for the south Pacific, 

 asserted, in 1772* "I am fully convinced that the flood comes 

 from the southward, or rather from the southeast." Laplace 

 seems to have entertained a similar idea for the Atlantic, and 

 assigned a day and a half as the time it took a wave to come from 

 the " main ocean."' 



The earliest attempt to draw cotidal lines was in 1807, by Dr 

 Thomas Young. t It is a sketch of the British islands, with coasts 



mi/ / 



Figure 1 



of France and Norway and progressive tidal lines. The lines 

 were drawn straight, crossing the English channel nearly at right 

 angles to its axis, and in other places springing squarely off from 

 the shores. In a supplement to the Encyclopaedia Britannica, 

 written in 1823, Dr Young suggested the tracing of cotidal lines, 

 indicated sources of data, declared the scheme impracticable, 

 but collected and reduced the data for 150 stations, and described 



*PhiI. Trans., 1772, p. 357. 



f Lectures on Natural Philosophy, vol. i, pi. xxxviii. 



