shore. The temperatures off both shores 

 may, therefore, be combined as shown below. 

 The number of records is shown in paren- 

 theses. 



Proper comparisons indicated that the 

 1930 and 1931 records of all months from 

 May to September and of all regions may be 

 combined to ascertain the discrepancies 

 between the bottom temperatures of the shal- 

 low and deep stations. The temperatures 

 averaged 4.3* (39,7° F,) in the shallow 

 waters that averaged 61 meters (200 ft,) 

 and 4,0° (39,2° F . ) in the deep waters with 

 an average of 114 meters (374 ft,). The 

 bottom temperatures actually declined gra- 

 dually with increased depths as shown in 

 the following table. 



Since no significant differences were 

 observed between the average bottom temper- 

 atures of 1930 and 1931 and of the several 

 months, they were combined to compare the 



data of various regions, although the depths 

 of the waters had to be considered. The 

 temperatures of depths beyond 185 meters 

 (607 ft.) and of October and November were 

 excluded. The trends were the same along 

 both shores. Data of the opposite regions 

 have, therefore, been combined as recorded 

 below. The number of records is shown in 

 parentheses. It appears that although the 

 average bottom temperatures decreased con- 

 sistently from south to north the discrep- 

 ancies were small not exceeding 0.3° (0.54° 

 P.). 



STATIONS IN 

 UPPER LAKE MICHIGAN PROPER 



Temperatures were obtained on 46 

 days in Upper Lake Michigan proper during 

 June 3-September 12, 1932, and on three 

 days during June 17-July 7, 1930 (table 9). 

 The depths ranged from 32 to 79 meters 

 (105 to 259 ft.) and averaged 64 meters 

 (210 ft.) at 17 designated shallow stations 

 and varied from 82 to 144 meters (269 to 

 472 ft.) and averaged 110 meters (361 ft.) 

 at 23 deep stations. Surface temperatures 

 recorded on the same day or two consecutive 

 days showed differences between 2 deep or 

 2 shallow stations as great in a restricted 

 section as in widely separated areas or as 

 between shallow and deep waters during the 

 same periods. The waters of the upper lake 

 are, therefore, considered a unit through- 

 out the period of observation with respect 

 to temperatures. 



During June 3-10 the surface temper- 

 atures rose from a minimum of 5.7° (42,3° 

 F,) to 10,5° (50.9° F.); the average was 

 7.9° (46.2° F.). The limits of the other 

 periods are based on the similarity of the 

 temperatures. Only the average tempera- 

 tures need to be compared. The average 

 increased from 15.2° (59.4° F. ) of the 

 period June 14-July 14 to 18.0° (64,4° F.) 

 during July 19-30, 19.7° (67.5° F.) during 



Shallow stations 



Deep stations 



Meters Feet 



4.1(18) 39,4 

 4.0(24) 39.2 

 3.9(27) 39.0 



24 



