174 POPULAR LECTURES AND ADDRESSES. 



elation, 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 

 Association. 1 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 

 declinational 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 (Fig. 27) we have (in the equilibrium 

 theory) higher water at lunar noon than at lunar 

 midnight. That difference in the height of high- 



1 Note of September 17, 1887. On the subject of Tidal Har- 

 monic Analysis see " Manual of Instructions for Tidal Observa- 

 tion," by Major Baird, published by Messrs. Taylor and Francis, 

 London, 1886 ; also the Reports of the British Association Com- 

 mittee "On Harmonic Analysis of Tidal Observations." W. T. 



