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IOWA ACADEMY OF SCIENCE 



As might be expected the tidal effect (estimated at .0016 inch) 

 could not be detected at all in a direct reading device of this 

 kind; but the conditions involved deserve attention. The dis- 

 tance from the laboratory to Arnold's Park (west to east) is 



Fig. 4 — The recorder of variations in the level of the lake. 



two and three-fourths miles. From this line north to the head 

 of the lake the distance is three and a half miles, approximately 

 the same as the east and west stretch of water. When the east 

 and west stretch alone is considered it should be low tide when 

 the moon rises and high tide when the moon sets, with neutral 

 effect when the moon is on the meridian. When the north and 

 south stretch alone is considered it should be high tide when the 

 moon is on the meridian, with neutral effect when Vhe moon 

 rises and when it sets. Thus even these minute differences 

 almost exactly neutralize each other. 



Oscillations due to changes in barometric pressure were also 

 too minute to be detected by direct registration without magnifi 

 cation. One of several computations made to ascertain the mag- 

 nitude of such oscillations resulted as follows : On June 30 the 

 weather map gave a barometric pressure of .00041!/^ pounds 

 per square inch at West Okoboji (at the. north end of the lake) 

 in excess of that at the laboratory, which pressure would be 

 counterbalanced hydrostatically by a rise of .00095 inch in the 

 level of the lake at the laboratory. This difference in barometric 

 pressure was one of the most marked differences that occurred 

 during the period of observation. 



