BAROMETRIC PRESSURES ON THE GREAT LAKES 



69 



lag determinations in this case, 0.1 hour, therefore corresponded to a dis- 

 crepancy in elevation of the water surface of less than 0.01 foot. 



TABLE No. 15. 



For the purposes of this table the words hour and hours are designated as hr. 



Values marked with minus signs are negative lags or anticipations. 



* In these cases no determination of the lag was possible, because the two values of which 

 the ratio should serve to determine the lag were of opposite sign. 



fThis value, not determinable from the observations, was assumed to be +6 hours, the 

 same as the lag as determined for the E-W effects at this station. 



STUDY OF PROPORTIONALITY FACTORS. 



Additional evidence as to the accuracy and reliability of the computed 

 barometric effects is afforded by a study of the proportionality factors P 

 and P n at the various stations. 



The formula (16) and (17), page 16, for barometric effects were derived 

 upon the assumption that the water of the lake remained continuously in 

 equilibrium under the influence of gravity and the barometric pressure. The 

 proportionality factors P w and P n were then introduced (see pages 16-18) to 

 take account of the modifications which would probably be produced by fric- 

 tion and by inertia. It was recognized that such modifications would prob- 

 ably be dependent to a considerable extent upon the configuration of the 

 shores and bottom of the lake and might to a considerable extent be peculiar 

 to each gage location. The modified equations for barometric effects 

 which were the basis of this investigation are shown as (18) and (19) on 

 page 17. 



