14 



Indiana University Studies 



From this set of readings it is certain that no water was returning 

 to the windward side of the lake along either shore. It appears that 

 the water from the entire lake surface was at first moved toward 

 the lee side of the lake. The contour of the shores modified the 

 inshore currents and concentrated the water at the embayment 

 on the lee side at Boys' City. This piling up of the water at this 

 point produced a state of unstable equilibrium so that a return 

 current was set up. As the effect of the wind increased this return 

 current involved all the water from surface to bottom for some 

 distance out in the lake, certainly more than 150 ft. The point 

 where the return current passed beneath the wind-driven water 

 was not determined since our anchor would not hold the boat. 



In this lake there are no return currents near the shore such as 

 Juday postulates as possible nor are the conditions similar to those 

 described for Loch Ness by Wedderburn (1910, p. 124) when he says : 

 ''It also appeared that the return current was nearer the surface 

 at the windward than at the lee end of the lake, which is natural, 

 as it might be expected that they would follow the direction of the 

 isotherms." 



Oxygen 



The oxygen was determined by the Winkler (1888, 1889) 

 method. This method was introduced into lake work almost 

 simultaneously by Birge and Juday (1911) and Bronstedfc and 

 Wesenburg-Lund (1911), and is certainly the most accurate and 

 best adapted to lake work of any method available. The oxygen 

 was usually determined at 2-meter intervals to 10 meters, and then 

 at 5-meter intervals to the bottom. In the epilimnion, the oxygen 

 in the water approaches the saturation point. It is evenly dis- 

 tributed in windy weather, but during periods of stagnation the 

 curve becomes irregular. If there happens to be a relatively 

 luxuriant growth of algae at some particular level, and the water 

 above is not turbid, these plants by photosynthesis will often 

 make a noticeable increase in the oxygen at this level. This 

 amount often exceeds the saturation point. The levels, tempera- 

 tures, etc., of the supersaturations we have found are shown in 

 the table below: 



As I have stated above, ''surface" in these tables means on 

 the average about 1 dm. below the surface. It often happens 

 that there is less oxygen near the surface than in some of the lower 

 levels of the epilimnion. This is not always due to the increase 



