MICHIGAN ACADEMY OF SCIENCE. 41 



showing the direction of the wind. At Saginaw, W. S. and Bay City the amount of varia- 

 tion was 23°, and at Midland 24°. Our maximum observation on land is 5° less than 

 for Saginaw, 2° less than at Bay City, while Midland is 8° lower. The maximum land 

 observation is 4° less than at West Saginaw, 1° less than at Bay City and 10° higher 

 than at Midland, showing somewhat more stable conditions. Likewise the minimum 

 water temperature is 1° more than at Saginaw, 4° greater than at Bay City and 12° greater 

 than for Midland. Maximum water temperature is 15° less than at West Saginaw, 12° 

 less than at Bay City, and 2° less than at Midland. It is apparent, as we shall see further 

 on, that this would very considerably modify the temperature near the adjacent shore 

 with the wind from off the water. 



It rained during the night of August 15 and 16, clearing up by noon time, the wind being 

 from the northeast during the period of fair weather. Our land temperature increased 

 17.7°, water temperature 8° or 45 per cent. This very considerably higher ratio of the 

 water is very likely due to the action of the wind sweeping down the bay exposing rela- 

 tively a larger water surface to the wind within a unit of area, and to the action of the 

 waves in entrapping particles of air. Not having the temperature of the rain water w'hich 

 fell during the night it is impossible to state how this would modify that of the water in 

 the bay. The increase of the water temperature during the day dropped only 3° from 

 7:00 p. m. to 5:30 a. m. the next morning, while that of the land fell 9° in the same interval. 

 It is apparent that under such water conditions, and with the breeze on shore, we would 

 have the climate somewhat modified, the main tendency being to check sudden variations 

 of land temperature and to increase the same. While the maximum amount of land 

 temperature increased 17.7° that at Midland varied 20°, at Bay City 21°, and. at West 

 Saginaw 22°, showing a slightly modified temperature variation when compared with the 

 preceding day as well as for the day under discussion. On land our minimum temperature 

 was 12° higher than for Midland, 2° higher than for Bay City and 1 ° higher than at Saginaw, 

 indicating a consideralile amelioration of conditions near the bay. On the other hand 

 maximum observations were 9.7° loAver for Midland 1.3° higher for Bay City, and 3.3° 

 greater for West Saginaw. Comparing the maximum and minimum water temperatures 

 with those at the three cities inland we find that the lowest minimum at Midland was 

 19°, at Bay City 9° and at Saginaw 8° less. Reversely the maximum at Midland was 

 7° lower than the bay, at Bay City 4° higher and at Saginaw 6° higher. 



August 17, the day was clear with the wind from the west during a greater part of the 

 forenoon, and shifting to the north by 1:00 p. m. The land temperature increased 18°; 

 that of the water 6° or 33 per cent, being somewhat inteimediate between periods when 

 the wind is off and on shore. The main trend of the bay is noitheast. At Bay City the 

 total amount of variation Avas 15°, at Saginaw 22° and at Midland 24°. It is apparent 

 that this northerly wind was quite pronounced in ameliorating the climate of Bay City 

 which is situated directly south of the bay "about 1 .5 miles. It is also apparent that Saginaw 

 is benefited to a considerable lesser extent, being some 14 miles farther south, the result . 

 is much less noticeable. Apparently these on shore winds' are only pronounced in modify- 

 ing climatic conditions within relatively circumscribed areas. This deduction is also 

 Ijorne out by an examination of the isothermal charts of lower Michigan for 1903 and 

 1904 to which we have already had occasion to refer. An average of 12 readings on land 

 and water gives 72.8° for the former and 73.9° for the latter, at our station near Tobico 

 bay. The minimum land temperature there was 2° greater than for Bay City and Saginaw, 

 and 12° greater than for ^Midland to the westward. On the other hand the maximum 

 land temperature at Midland was 6° lower, at Bay Citv 5° lower, and at Saginaw 2° higher. 

 I believe that insular climates are more pronouncedly influenced in preventing minima 

 temperatures than the reverse. As we shall see farther on this is due to the very con- 

 sideral:ile capacity water has of absorbing heat during the day and retaining the same to 

 a greater capacity at night. Comparing the minimum water temperature our readings 

 near Tobico show the water 9° warmer than the land there, at Midland 21° warmer, at 

 Saginaw and Bay City 11° warmer. With the maximum water temperature the ther- 

 mometer at Midland was 3° colder and at Saginaw 5° warmer. 



During August 18 the sky was clear with an easterly wind blowing on shore. The 

 land temperature only increased 18° while that of the water increased 9° or 50 per cent. 

 Comparing this with those previously discussed it was noted that with a noith wind blowing 

 diagonally across the bay, that the ratio of water to land temperature was 33 per cent, 

 with a northeasterly wind blowing down the bay of 45 per cent, while that from the east 

 as just given is 50 per cent. While theoretically we might expect the greater increase 

 of water temperature with a full Iireeze coming from the northeast down the main trend 

 of the bay, this result is very probably modified by the shallow waters of the lower reaches 

 of Saginaw bay. giving greater plav to wave action. This on shore action, as noted above, 

 is not only pronounced in increasing relatively the greater warmth of the water, but also 



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