379 



TABLE 1. 



Showing the half-hourly (and in two places the quarter-hourly) 

 co-ordinates of altitude of the average semi-diurnal lunar tidal 

 wave at Chicago, on Lake Michigan, derived from 9184 obser- 

 vations made between January \st and July \st, 1859. 



The accompanying profile, marked Fig. 1, shows the mean semi- 

 diurnal tidal wave at Chicago, projected from the foregoing co-ordi- 

 nates, embracing every vicissitude of winds and weather, &c., which 

 occurred during the whole six months' observations. It shows the 

 altitude of this mean tidal wave to be, at its summit, one hundred 

 and forty-six thousandths (.146) of a foot, equal to If inches; and 

 the average time of high-water is thirty minutes after the time of 

 the moon's meridian transit. 



