8 EFFECTS OF WINDS AND OF 



at any one time at various intervals since it was commenced in the summer 

 of 1911. In all, 31 persons have taken part. I have spent more than 2,000 

 hours on the investigation, none in routine work. 



OUTCOME OF THE INVESTIGATION. 



The outcome of the investigation may be very briefly characterized as 

 follows : 



(1) Reasonably accurate numerical expressions have been obtained for 

 the effects of barometric pressures on the elevation of the water surface at 

 the five stations, Buffalo, Cleveland, Milwaukee, Mackinaw, and Harbor 

 Beach, on Lake Erie and on Lake Michigan-Huron. With these expressions, 

 one may, from the distribution of barometric pressures ordinarily shown on 

 the forecast maps of the Weather Bureau, compute the disturbances in 

 elevation of the water surface thereby produced at the stations named. 



(2) The general method has been developed by which such a numerical 

 expression for the barometric effect at any station on any body of water may 

 be derived from observations of the water elevation at that station and the 

 forecast maps for the same period. 



(3) A general expression, including the necessary numerical constant, has 

 been obtained for the effect of winds, of any given velocity and direction, in 

 producing a disturbance of elevation of the water surface at any given sta- 

 tion, on any body of water, anywhere in the world. The data required in 

 regard to the station and the body of water are such as are ordinarily shown 

 on good charts, namely, the depths of the water at all points, the location of 

 the shore line, and the location of the station. 



(4) Four of the prevailing seiches, or free oscillations under the influence 

 of inertia, on Lake Erie and Lake Michigan-Huron have been isolated. 

 Their periods and probable methods of oscillation have been shown. The 

 relation between these seiches and the uncertainties in daily mean elevations 

 of the water surface at gage stations has been discerned. The appreciation 

 of this relation aids decidedly in obtaining accurate determinations of the 

 daily mean elevation of the mean surface of each lake. 



(5) The accuracy with which the elevation of the mean surface of any one 

 of the Great Lakes may be determined for any given day has been decidedly 

 increased. On Lake Erie the elevation of the mean surface of the lake may 

 now be determined as accurately from one day of observation at Buffalo 

 as it was formerly possible to fix it from 16 days of observation at that sta- 

 tion. Similarly, the elevation of the mean surface of Lake Michigan-Huron 

 may now be determined as accurately from one day of observation at Mack- 

 inaw as it was formerly possible to determine it from 6 days of observation 

 at that station. When one determines the fluctuation of elevation of the 

 mean surface of a lake he thereby determines the fluctuation in the total 

 water-content of the lake. 



(6) The relations of the new knowledge indicated in (1) to (5) to four out- 

 standing problems have become evident. The four problems are: 



