372 Prof. G. H. Darwin. On an Apparatus for [Dec. 15, 



The values of <f and of \ne will be different for each kind of tide, 

 and the following table gives their numerical values. 



As it does not appear worth while to evaluate the tides written 

 below the line, no use will be made of the last six results given in 

 this table. 



7. On the periods over which the means are to be talten in evaluating 

 the tidal constants. 



We have considered in previous sections the treatment of the group 

 of tides which are associated with solar time, when the period of ob- 

 servation is less than a year, and we have now to consider the other 

 tides. 



It is important that the means be taken over such a number of 

 days that the perturbation arising from other tides shall be mini- 

 mised. 



The perturbation between semi-diurnal and diurnal tides is always 

 negligible. It is therefore only necessary to consider the action of the 

 tides M 2 , S 2 in the case of semi-diurnal tides, and that of K x and O for 

 diurnal tides. 



