108 



EFFECTS OF WINDS AND OF 



mean observed elevations and for the Lake Michigan-Huron mean cor- 

 rected elevations, are of a high degree of accuracy. The determination of 

 relative accuracy must be made mainly by other methods in this case. 

 However, an examination of the two graphs makes it clear that both are of a 

 very high degree of accuracy. 



MONTHLY AND SEASONAL MEAN ELEVATIONS. 



The following tables, No. 26 for Lake Erie and No. 27 for Lake Michigan- 

 Huron, show the monthly and seasonal mean observed elevations and mean 

 corrected elevations of the water surface, first, for the separate gage stations, 

 and in the last two columns for the lake as derived from the means from the 

 stations named. These means monthly and seasonal are based directly 

 on the values shown in tables Nos. 19 to 25, and on similar tables, which are 

 not published, for the season of 1909 on Lake Erie and the season of 1910 

 on Lake Michigan-Huron. 



TABLE No. 26. 

 [Mean observed and mean corrected elevation =570+ feet.] 



PROBABLE ERRORS AND WEIGHTS. 



The residuals as tabulated in tables Nos. 19 to 25, inclusive, are evidently 

 a test of the accuracy of the observed elevations and of the corrected ele- 

 vations corresponding to these residuals. It is desirable to study these 

 residuals and formulate the conclusions from them. 



If N independent determinations are made of a quantity which is constant, 

 and the residuals are taken of the separate determinations from the mean of 



