BAROMETRIC PRESSURES ON THE GREAT LAKES 79 



The column marked "5-day corrected mean" bears the same relation 

 to the corrected elevations as the column marked "5-day observed mean" 

 does to the observed elevations. The explanation made in the preceding 

 paragraph for groups containing six values or less than five values also 

 applies to the corrected elevations and 5-day corrected means. 



In the column "Corrected elevation," an occasional value is inclosed in 

 parentheses and the corresponding residual is also inclosed in parentheses. 

 Each corrected elevation contained in a parenthesis, such, for example, as 

 2.36 on June 2, 1910, at Buffalo, is one which has been identified by a definite 

 criterion, based on the preceding investigation, as being an abnormal dis- 

 turbed value which should be rejected in taking means. It is so re- 

 jected in this tabulation. , The criterion wijl be stated later in the proper 

 context. 



The residuals of the daily observed elevations from the 5-day observed 

 means, and the corresponding residuals of daily corrected elevations from the 

 5-day corrected means, as shown side by side in the last two columns of the 

 table, furnish an instructive indication of the relative accuracy of the 

 observed and corrected elevations. 



The preceding general explanations also apply to tables Nos. 20 to 23. 



MEAN ELEVATIONS OF LAKE ERIE. 



In tables Nos. 19 and 20 there are given elevations of the water surface of 

 Lake Erie as observed at the Buffalo gage and at the Cleveland gage. 

 Before this investigation had been made, the best available approximation 

 to the mean elevation of the whole surface of Lake Erie on a given day 

 would have been assumed to be the mean of these two observed elevations 

 at the two gages. Also, there are given in tables Nos. 19 and 20 the cor- 

 rected elevations from those gages. Each such corrected elevation is a 

 value for the elevation of the mean surface of Lake Erie after the cor- 

 rections have been applied for disturbances at each gage by barometric pres- 

 sures and by winds. The mean of these two corrected elevations, one for 

 the Buffalo gage and one for the Cleveland gage, is recognized from this 

 investigation to be the best approximation, on any given day, to the mean 

 elevation of the whole surface of Lake Erie for that day. 



Table No. 24 serves to place in juxtaposition these two mean values of 

 the mean elevation of the whole surface of Lake Erie, one without corrections 

 and the other with corrections for barometric effects and wind effects. The 

 table serves to enable one to compare the two sets of values, study their ac- 

 curacy by means of the 5-day means and the residuals, and so make prog- 

 ress in testing the over-all accuracy and reliability of the barometric cor- 

 rections and wind corrections. 



In table No. 24 the observed elevation for any day was obtained by 

 merely taking a mean of the two observed elevations for that day as re- 

 corded in table No. 19 for Buffalo and table No. 20 for Cleveland. 



