42 SEVENTH REPORT. 



pari passu, in modifying that of the adjacent land to the west. It is also true' that the 

 modification of temperature would be greater during the night. Comparing the land 

 minimum with that of the water near Tobico we hnd the water 9° warmer at 5:30 a. m. 

 and 3° warmer at 6:45 p. m. At Midland the temperature was 14° colder; at Bay City 

 and Saginaw 10° colder. Relatively, however, Midland was much warmer than the usual 

 ratio of temperatures with Bay City and Saginaw, very likely due to this easterly Avind. 

 The maximum land temperature at Tobico was 5.2° greater than at Bay City, .8° less than 

 at Saginaw, 2.8° less than Midland, and .1° less than the bay, showing quite stable climatic 

 conditions under these circumstances. Reversely our water minimum was 9° greater 

 than the land near Totjico, 23° greater than at Midland and 19° greater than at Bay City 

 and Saginaw. The water maximum was 5.3° greater than a^t Bay City, .7° less than 

 at Saginaw, and 2.7° less than Midland, indicating a constantly increasing divergence 

 going away from the bay. 



During August 22 and 23 observations were taken consecutively from 1 p. m. to 11:15 

 a. m. The weather was clear, wind from the northwest, shifting to the west during the 

 morning of the 23rd. During that time the land temperature fell from 76° at 3 p. m. 

 to 50° at 5:30 a. m., or 26°, the maximum change of water temperature during approxi- 

 mately the same time being 8.5° or 32.6 per cent, of the change on land. During the 

 forenoon of the 23rd the land temperature rose 24° by 11 :15 a. m. and the water temperature 

 increased 5.7° within the same time, or 23.75 per cent. While during the afternoon the 

 maximum land temperature was 1.8° greater than the water at 5.30 a. m. the next morn- 

 ing the lowest land temperature was 16° less than the minimum water temperature, show- 

 ing the very considerable capacity of the water to retain heat during the night. Our 

 maximum land temperature near Tobico is 1° greater than at Bay City and 2° less than at 

 Midland and West Saginaw. On the other hand our minimum land temperature was appar- 

 ently 8° less than at Bay City, 9° less than that of Saginaw, and 10° less than Midland. 

 Maximvun and minimum land temjieratures on the other side of the bay, and in the path 

 of the wind, would be of value in this connection. Comparing our water maximum of 

 the 22nd with that of the land, we find Bay City .5° greater, i\Iidland and Saginaw 3.5° 

 greater. The wind, however, l)eing from the northwest and west, M'e would expect greater 

 modifications of land temperatures over in the "Thumla," rather than in the places above 

 mentioned. The minimum water temperature on the 23rd is 22° greater than for Midland, 

 21° more than at Saginaw and 8° greater than at Bay City, showing to what extent the 

 temperature of Bay City was benefited by its jjroximit}' to the bay. An average of our 

 land and water temperatures near Tobico are respectively 64.5° and 69.9° during the entire 

 period of about 24 hours. 



During the 24 hours ending at 5:30 a. m., August 26, 1904, we haA'e a continuous series 

 of land and water temperatures. The weather was fair with quite a strong westerly 

 wind blowing throughout that time. The average of 18 readings give a land temperature 

 of 67.07°, that of the water being 69.9° for the same time. During the 25th the land and 

 water temperature increased 13° and 7.5° respectively, the ratio Ijeing 57.6 per cent, 

 followed by a minimum drop of 39° and 12.2° of the land and water at 5:00 a. m. on 

 the 26th of the following morning, or only 31 per cent of change of the water relative to 

 the land. Land and water temperatures taken simultaneously on the other side of the bay 

 would be desiral^le for comparison here. These readings, however, clearly show the prop- 

 erty water has of absorl^ing and retaining heat. During the 25th our maximum land tem- 

 perature was 85° with 80° for Midland, 82° for West Saginaw and 83° for Bay City. Re- 

 versely our minimum land temperature on the morning of the 26th is 46° near Tobico, 43° 

 for Saginaw, 44° for Bay City and 60° for Midland. To show clearly the cause of insular 

 climate it would be well to have inaximum and minimum land observations on the east 

 side of the bay in the "Thumb" for comparison with those at Midland to the westward. 

 During the same time our maximum and minimum water temperatures were 75.5° and 63.3° 

 as compared with those given above. 



The average of all these observations gives an average water temperature of 72.11°, 

 that of the land being 72.38°. It is more probable, however, as shown by our readings 

 for 24 hours, that the average water temperature is about 4° greater during the latter 

 part of August than that of the land. The ratio of change of water temperature relative 

 to that of the land is less than 34.4 per cent. In this factor, taking into account the pre- 

 vailing southwesterly winds, is at least a partial explanation of the insular climate of 

 lower Michigan. Moreover the temperature of the water, as a rule, being greater than 

 that of the land from about 7 o'clock in the evening until about 9 o'clock the following 

 day, the tendency would be to increase the temperature of the adjacent shores. On the 

 other hand, the land tefiiperature being greater during the remainder of the day, the water 

 would tend to establish an equilibrium negatively, the two means of variation probably 

 approaching that of the average of the two factors, land and water. The more prolonged 



