Chap. IX.] SOLAR AND LUNAR GRAVITATION. 109 



the sun, than by the present method of taking as the 

 ' establishments ' the hours at which the first high 

 tide occurs at the various ports after the sun and 

 moon being in conjunction or opposition. 



For the time when the earth's course round the 

 moon is in conjunction with its course round the sun 

 is the normal hour of the monthly conjunction of the 

 lunar with the solar tide, and therefore the ' priming ' 

 and ' lagging ' of the tides throughout the month 

 may be calculated in a more simple and accurate 

 manner by considering this as the commencement 

 and close of the tidal months, and by reckoning the 

 cj^cle of variations in the alternate ' priming ' and 

 ' lagging ' of the tides through these intervals, instead 

 of through the intervals between the times of new 

 moon. 



