line must continue to rise for some time even though 

 the level at Buffalo is falling. Thus the level at Port 

 Stanley would reach a maximum some time after the 

 Buffalo maximum (always assuming the nodal line to 

 be west of Port Stanley), and this would also account 

 for the larger observed amplitude than might be ex - 

 pected near the nodal line. Figure 21 illustrates the 

 foregoing suggestion. Third, the 14-hour oscillation 

 may give rise to a progressive wave originating from 

 either Long Point or the point at Rondeau Harbor 

 which upon reaching Port Stanley would cause the de- 

 layed maxima and minima. 



It is frankly admitted that the true cause of the 

 lag is not known, and that the problem will no doubt 

 remain unsolved until additional field observations 

 are made. 



The presence of two primary seiches, or oscil- 

 lations, is well established. The best available 

 values for their periods are 14. 1 hours for the length- 

 wise (east -west), and 2. 7 hours for the crosswise 

 (north -south) oscillations. These values are believed 

 to be correct within 0. 2 hour. 



The marginal zones of the lake are usually 

 very muddy during and immediately following on- 

 shore storms, and the line of demarkation between 

 the muddy water and the deeper, clear water is 

 often very sharp. This line of demarkation runs 

 parallel with, and 1-4 miles from, the shore line, 

 depending on the depth of water. As only a few 

 of the stations are near the shore, observations were 

 seldom made in muddy water. Aside from the sea- 

 sonal increase, it is evident that both the quantity 

 of plankton and the amount of bottom silt held in 

 suspension during the following storms are the pri- 

 mary factors controlling the transparency. 



The most favorable situation for high readings 

 at a given station was a clear day with the sun 2 or 3 

 hours from the meridian and when the observation 

 was taken on the lee and shady side of the boat. 

 The light rays reflected from the surface did not then 

 interfere with vision. At a favorable position, the 

 transparency was as much as 10 percent greater than 

 at an unfavorable position. 



TRANSPARENCY 



The Secchi-disc readings for all of the stations 

 are listed with the station data (table 6). The max- 

 imum reading of 12. 3 meters was obtained at sta- 

 tion 54 on September 6, 1929, after several days of 

 comparatively calm weather; and the minimum 

 readings of 0. 6 meter occurred at station 26 on May 

 20, 1929. On both occasions the sea was choppy and 

 the sky cloudy. The maximum and minimum values 

 during the 1928 survey were 10. 5 and 2. meters. 



The monthly means of the readings over the 

 whole lake in 1929 were: June, 2. 5 meters; July, 

 3. 3; August, 4. 1; September, 6. 1; and the mean of 

 the 19 stations occupied in May was 1.0 meter. 

 Thus the mean transparency increased as the season 

 advanced. 



The decrease in transparency following a period 

 of stormy weather is well illustrated in the Septem- 

 ber observations. During this month we find a mean 

 of 8. 5 meters for the stations east of Erie, Pa. , and 

 a mean of only 3. meters for the remainder of the 

 lake. The observations over the eastern part were 

 taken during the following moderate to calm weath- 

 er, and those of the western part following a week 

 of very stormy weather. 



