^2 , Public Parks. 



quantity of rain that falls, and causes local currents of air, thus 

 partially changing the prevailing winds of this latitude, producing 

 necessarily local changes of temperature. These local undulations 

 are most marked in the spring, owing to the fact that the specific 

 heat of land is only one-quarter that of water, and it both absorbs 

 and gives it out more rapidly ; while water, on the other hand, 

 absorbs it more slowly, stores up a greater quantity, and parts with 

 it less readily, owing, no doubt to the difference in the conducting 

 and radiating properties of both. It is mainly owing to this fact 

 that our springs are so cold, raw, and long continued ; that is, the 

 water is not as soon heated as the land, thus giving rise to local 

 changes of temperature, and of winds. In the autumn the heat 

 of the water is less readily abstracted than that of the land, thus 

 causing the temperature in the immediate vicinity of the lake to be 

 milder than even at localities further south and west, as, during 

 last September, October, and November, the mean temperature 

 of Springfield, was nearly the same as at Chicago.* This was no 

 doubt owing to the fact that the temperature of the lake was more 

 than ordinarily high in July and August ; as, on July 20th, the ther- 

 mometer indicated 72°t at a depth of thirty feet, while the mean 

 temperature of the air, on the same day, was 83% and even 

 later the extraordinary warmth of the water that passed through 

 the Tunnel attracted attention, and it was supposed that the water 

 supplied to the city, did not come through the Tunnel, and that an 

 accident had occurred, and the supply was being pumped up from 

 near the shore. The mean temperature of the lake is no doubt the 

 same as that of the land for the year, differing only in the absorbing 

 and parting power of heat ; as is evidenced by the fact that the 

 freezing point only obtains a short distance from the shore. It will 

 therefore be seen how, for eight months of the year, and sometimes 

 even nine, the lake exercises a wholesome inffuence upon the health, 

 counteracting, to some extent, the great and sudden changes incident 

 to our level and open topography, while during the remaining 

 months it is injurious to health, on account of the cold and chilling 

 eflfect it has, in addition to causing sudden changes. Owing to its 

 large evaporating surface, it supplies a large amount of the oxygen 

 that is consumed here, thus purifying the atmosphere. 



* A gricuUural Bureau Reports. 

 t Langguth. 



