170 



ANNUAL OF SCIENTIFIC DISCOVERY. 



On a close examination of all the observations embraced in this series, we 

 find one hundred and eighty-nine which we think ought to be rejected, 

 because influenced in an extraordinary decree by unfavorable winds, and we 

 think the average semi-diurnal lunar tidal-curve should rather be adopted, as 

 shown by the remaining eight thousand nine hundred and ninety-five obser- 

 vations. 



The general result will then stand as shown in the preceding Table (II.), 

 page 169. 



Under this view we have one hundred and fifty-three thousandths of a foot, 

 or l^ 8 ^ inch, as the general average height of this semi-diurnal tidal-wave 

 at its summit; and thirty minutes after the moon's meridian passage still 

 appears to be the average time of lunar high-water. 



A separate tabulation was made, for every quarter-hour of interval, of all 

 the observations which occui'red from twelve hours before to twenty-four 

 hours after the periods of new and full moon, for each lunation. In this way 

 we hoped to obtain, at each new and at each full moon, six semi-diurnal tides, 

 each of which would approximately represent a semi-diurnal spring-tide, and 

 a mean of all would tend to eliminate errors arising from the disturbing 



TABLE III. Shoiving the quarter-hourly coordinates of altitude of tJie average 

 semi-diurnal lunar spring tidal-wave at Chicago, on Lake Michigan, as 

 derived from 1200 observations made at and near the several periods of New 

 and Full Moon, between January 3d and June 2d, 1859. 



1 Low-water of lunar spring-tide. 2 Moon on Meridian. 



3 High-water of lunar spring-tide. 



4 Slightly discrepant, owing to a preponderance of unfavorable winds at this 

 particular period. 



