4 EFFECTS OF WINDS AND OF 



the whole surface of each lake. The manner in which the conclusions 

 reached in this investigation may be applied to other lakes or bodies of water 

 and may help in solving various problems is briefly indicated. 



DATA USED AND ACKNOWLEDGMENTS. 



No new observations were made in this investigation. The necessary 

 observations, in great abundance, and of adequate accuracy and reliability, 

 had already been made. The principal data used include hourly and daily 

 observed elevations of the surface of Lake Erie and Lake Michigan-Huron 

 at five gage stations, observed hourly wind directions and velocities at five 

 points near these two lakes, and the observed barometric pressures twice 

 per day at six points. 



The hourly elevations of the water surface which were used on Lake Erie 

 covered 48 selected days at Buffalo and 52 selected days at Cleveland. On 

 Lake Michigan-Huron the hourly elevations of the water surface which were 

 used covered 34 days at Milwaukee, 42 days at Harbor Beach, and 42 days 

 at Mackinaw. 



The daily mean elevations of the water surface which were used on Lake 

 Erie covered the months August-October 1909 and June-October 1910 

 eight months in all. Each daily mean was the mean of 24 hourly values for 

 that day obtained from the records of the automatic gages which had 

 operated at Buffalo and Cleveland. The two sets of daily means were 

 entirely separate and independent for the two stations Buffalo and 

 Cleveland. 



On Lake Michigan-Huron the daily mean elevations of the water surface 

 which were used were separate and independent series at each of the three 

 stations, Milwaukee, Mackinaw, and Harbor Beach, each covering the 

 months June-September 1910 and June-September 1911 eight months in 

 all. Each daily mean was the mean of 24 hourly values for that day obtained 

 from an automatic gage. 



The observed hourly winds which were used had been obtained from 

 recording anemometers and wind vanes as operated at the U. S. Weather 

 Bureau stations at Buffalo, Cleveland, Milwaukee, Port Huron (Michigan) 

 and Sault Ste. Marie (Michigan). For each hour the total travel of wind in 

 that hour was observed and the prevailing direction to the nearest of the 

 principal points, N, NE, E, SE, etc., at intervals of 45. The hourly winds 

 used at the stations named cover all of the months named in connection 

 with the daily mean elevations of water surface and also all of the separate 

 days for which hourly water elevations were used. 



The observed barometric pressures at six stations near the two lakes were 

 read from the isobars (lines of equal barometric pressure) as shown on the 

 daily forecast maps as prepared at the U. S. Weather Bureau at Chicago for 

 the use of the forecaster at that station. Two such maps are made for each 

 day, one showing the facts at 8 a.m., 75th meridian time, and the other facts 

 at 8 p.m., 75th meridian time. The barometric pressures used in this investi- 

 gation were for the two times named on each of the dates covered by the 



