In 1930 temperature readings were taken much earlier in the season 

 than in 1929, but they were not continued so far into the autumn period. 

 On April h, when the first temperatures were taken at Station l58, the mean 

 temperature was 2.9" (Table 10, Fig. 8). In the following weeks the tempera- 

 ture increased rapidly, and reached 22.2" on June 26, or somewhat earlier 

 than in 1929. The highest point of the season (25.0") was found on August 1, 

 very close to the time of maximum for 1929 as indicated by the record at Sta- 

 tion 8F. By August I9 the temperature had lowered to 22.11°, and by September ! 

 to 22.0". In the latter part of September the temperature fell rapidly, and 

 on October 1 it was about the same as on June 11. The records at Station 8F 

 and 37A are similar to that at Station l58, except that they show lower temp- 

 eratures for most of the comparable dates. 



If we compare the records of temperature at Station 158 for 1929 and 

 1930, we find that the water was noticeably warmer in 1930 (Tables 8 and 10; 

 Pi.g. 8). This fact is even more clearly shown in the records of Station 8F 

 (Tables 9 and 11; Fig. 9). The explanation may be found in the records of 

 air temperatures at Sandusky for those two years. Reference to Table k will 

 show that, on the average, each of the months of May, June, July, August and 

 September was warmer in 1930 than in 1929. April and October were warmer in 

 1929 than in 1930, but for April 1929 j data on water temperatures are lacking, 

 and the records of October 1930 were made very early in the month. 



The stations located in shallow water at the mouths of small rivers 

 showed a more rapid response to changes in air temperature than the stations 

 in deeper water; they were warmer in periods of rising temperature and cooler 

 in periods of falling temperature. The temperatures at Station 126 (Detroit 

 River) were similar to those at other stations in the open water of the west- 

 ern part of Western Lake Erie. During 1929 temperatures were taken at Sta- 

 tions 126, and 117 (off Monroe), within a period of two hours on five dates. 

 The mean of the five values was 19.65° at Station 126 and 20.6' at Station 

 117, or a difference of slightly less than 1.0". A similar but smaller dif- 

 ference was noted between Stations 126 and 13)4 (Middle Sister) on four dates 

 in the ?ame year. The explanation for the small difference is probably that 

 the water coming from Lake Huron is warmed considerably in passing through 

 shallow Lake St. Clair before entering Detroit River. Maumee Bay was charac- 

 terized by high temperatures diiring the summer period. 



Transparency 



Transparency was measured by means of a Secchi disc 20 centimeters in 

 diameter, painted entirely white. Readings were always made on the shady 

 side of the boat. The disc was lowered until it disappeared from view, then 

 raised until it appeared, and the mean of the two readings recorded. Read- 

 ings were male to the nearest one tenth meter. 



The water of Western Lake Erie is characterized by low transparency. 

 The highest reading taken during the two seasons of 1929 and I930 was ii.8 



ss 



