THE TIDES. 183 



pass Manual, this is to say, the coefficients in the 

 harmonic expression 



A + B sin e + C cos 9 + D sin 2 6 + E cos 2 Q, 



for the deviation of the compass in an iron ship. 



The first instrument which I designed and 

 constructed for use as a Tide Predicter was 

 described in the Catalogue of the Loan Collec- 

 tion of Scientific Apparatus at South Kensington 

 in 1876; and the instrument itself was presented 

 by the British Association to the South Kens- 

 ington Museum, where it now is. The second in- 

 strument constructed on the same principle is in 

 London, and is being worked under the direction of 

 Mr. Roberts, analysing the tides for the Indian ports. 

 The result of this work is these books (Tide Tables 

 for Indian Ports) in which we have, for the first 

 time, tables of the times and heights of high water 

 and low water for fourteen of the Indian ports. 



To predict the tides for the India and China 

 Seas and Australia we have a much more difficult 

 thing to do than for the British ports. The 

 Admiralty Tide Tables give all that is necessary 

 for the British ports, practically speaking ; but for 



