768 



The first column indicates the days when the 

 observations of 9h were nearest the epocha of 

 the syzygies, and quadratures. In the tempe- 

 rate zone a decade often suffices to ascertain 

 the periodicity of the atmospheric tides ; but the 

 preceding table renders it probable that within 

 the tropics, twelve days of observations, the 

 days of sizygies and quadratures, are not suffi- 

 cient to disengage the lunar effect from acci- 

 dental perturbations. More positive results 

 would be obtained, if, after having collected a 

 great number of observations made at the in- 

 stant of the passage of the sun and moon over 

 the meridian, the regular effects of the diurnal 

 period were defalcated. 



