THE TIDES 305 



and Beyt Harbour at the entrance to the Gulf of Cutch, 

 Bombay, Karwar, Beypore, Paumben Pass, Madras, Vizaga- 

 patam, Diamond Harbour, Fort Gloster and Kidderpore 

 on the River Hooghly, Rangoon, Moulmein, and Port 

 Blair. Mr. Roberts, who was first employed as calculator 

 by the Committee of the British Association, has been 

 asked to carry on the work for the Indian Government, 

 and latterly, in India, native calculators under Major Baird, 

 have worked by the methods and forms by which Mr. 

 Roberts had worked in England for the British Associ- 

 ation. 2 The object is to find the values of the different 

 tidal constituents. We want to separate out from the whole 

 rise and fall of the ocean the part due to the sun, the 

 part due to the moon, the part due to one portion of 

 the moon's effect, and the part due to another. There are 

 complications depending on the moon's position declina- 

 tional tides according as the moon is or is not in the 

 plane of the earth's equator and also on that of the sun. 

 Thus we have the diurnal declinational tides. When the 

 moon is in the north declination (Fie. 131) we have (in 

 the equilibrium theory) higher water at lunar noon than 

 at lunar midnight. That difference in the height of high 

 water, and the corresponding solar noon tides and solar 

 midnight tides, due to the sun not being in the earth's 

 equator, constitute the lunar and solar diurnal declina- 

 tional tides. In summer the noon high water might be 

 expected to be higher than the midnight high water, be- 

 cause the sun is nearer overhead to us than to our Anti- 

 podes. 



By kind permission of Sir Frederick Evans, I am able 

 to place before you these diagrams of curves drawn by 

 Captain Harris, R.N., of the Hydrographic Department 

 of the Admiralty, exhibiting the rise and fall of tides in 

 Princess Royal Harbour, King George Sound, Western 

 Australia, from January ist to December 3ist, 1877, and 

 in Broad Sound, Queensland, Australia, from July I5th, 



3 Note of September 17, 1887. On the subject of Tidal Harmonic 

 Analysis see " Manual of Instructions for Tidal Observation," by Major 

 Baird, published by Messrs. Taylor and Francis, London, 1886; also the 

 Reports, of the British Association Committee " On Harmonic Analysis of 

 Tidal Observation*." -W. T. 



