98 IOWA ACADEMY OF SCIENCE 



THE METEOROLOGICAL DATA. 



The month of July, 1915, is reported to have been an unusually 

 cold and rainy month for that time of the year. The maximum 

 temperature ranged between 70° and 87° Fahr., and the mini- 

 mum from 44° to 70.5° Fahr. The relative humidity varied 

 from 52 per cent to 100 per cent, was often close to 100 per cent 

 and very often above 90 per cent. The details of the data are in 

 the tables that follow, and are made use of in the analyses of the 

 curves. 



COMMENTS ON PLATES III AND 111 A. 



On June 30 the barometric pressure at the north end o£ the lake 

 in excess of that at the laboratory was sufficient to cause a rise of 

 .00095 of an inch in the level of the lake at the laboratory. The 

 preceding day there was no difference in the barometric pressure 

 at these two extremes, but there was a gradual fall in the level 

 of the lake, suggesting the need of a record of precipitation, evap- 

 oration, intake and outflow. Observations on precipitation and evap- 

 oration were begun July 5. 



July 1 the level of the water fell quickly a quarter of an inch on 

 change of wind from southeast to northwest. 



July 3 the excess of barometric pressure at the laboratory over that 

 at north end of the lake should have caused a lowering of the water 

 of .0021 of an inch at the laboratory and have maintained that differ- 

 ence that day and the next. To make such a variation evident the 

 apparatus should magnify the movement at least thirty times, and 

 preferably fifty. 



July 5 a light southwest wind during the afternoon, aided some- 

 what by evaporation, sent the pointer below the bottom of the scale. 

 July 7 the wind shifted to the nortneast, and the water rose quickly 

 one and one-half inches (from the bottom of the scale to that height), 

 which level it maintained approximately for about three days. 



July 7 the excess of barometric pressure at Arnold's Park over 

 that at the laboratory would cause a rise of .015 of an inch. 



July 8 the excess of barometric pressure at East Okoboji (north 

 end of the lake) would cause a rise of .03 of an inch in the level of 

 the water at the laboratory. 



July 12-15. If allowance be made for evaporation the general course 

 of the line is horizontal during a short period of clear weather with 

 medium to light winds. There are, however, rythmic curves noticeable 

 with a maximum variation of about one-fifteenth of an inch on the 12th, 

 13th and 14th, apparently due to variations in the wind; and also 

 variations lasting from one to three hours amounting to 1-30 inch for 

 which no suitable explanation is at hand. The long variations of ap- 



