158 STATE HORTICULTURAL SOCIETY. 



across the entire lake region, as if the whole surface were one unbroken land- 

 area. Still cruder is the isothermal chart of the United States "as determined 

 by the Smithsonian Institution,"* and published a year or two earlier than 

 Blodget's work. It will be understood, as a necessary inference, that the 

 charts based on the army observations,! as well as all previous attempts at 

 isothermal charts, fail totally to detect the local climatic influence which, as 

 we now know, bends the isothermal lines of our peninsula in the most extra- 

 ordinary manner. 



The peninsular situation of our State is something which arrests the atten- 

 tion of the most casual observer of the map of the northwest. It is not appar- 

 ent to observation, however, that our State is also a climatic peninsula ; and 

 yet, extended observation shows that our climate, in its seasonal means, is a 

 patch taken from the latitude of Ohio ; while in the moderation of its extremes, 

 it bears an analogy to the Floridian peninsula. Its climate is cut off from that 

 of Wisconsin and Iowa by a barrier as abrupt and as real as that which limits 

 our territory. That which constitutes the barrier in the one case, creates it in 

 the other. 



The nature of our climatic situation is exemplified in the comparative sta- 

 tistics of every cold wave which passes over the northwest. On the 18th of 

 November, 1880, for instance, while the thermometer was 5° at Milwaukee, it 

 stood at 18° at Grand Haven, and 10° at Port Huron. At the same time, it 

 was 8° at St. Louis, 2° at Denver, 4° at Dodge City, Kansas, and G° as far 

 south as Fort Gibson, Indian Territory. On the 19th of November, while the 

 thermometer marked 29° at Grand Haven, it was 13° at Port Huron ; and 

 farther south, it marked 14° at Chicago, 2° at Indianapolis, 11° at Louisville, 

 and 8° at St. Louis. 



The rationale of our peninsular climate is easy to understand. It involves 

 only two fundamental factors : 1. The presence of a large body of water on 

 our western boundary. 2. The prevalent westerly direction of our cold winds. 

 Lake Michigan is a body of water 360 miles long and 108 miles wide, with a 

 mean depth of 900 feet, and a superficial area of 20,000 square miles. You 

 could sink, in this lake, the three States of New Jersey, Delaware and Mary- 

 land. It contains 18| millions of millions of cubic yards of water,;}; or in 

 other terms, 3,400 cubic miles of water. This vast body of water maintains a 

 comparatively uniform temperature. Three months of summer warmth do not 

 suffice to elevate it much above the annual mean, nor three months of winter 

 to depress it much below that mean. While the mean July temperature of the 

 land, in the mid-latitude of Lake Michigan, rises to 74°, that of the lake 

 surface does not surpass 51°. While the January temperature of the land 

 sinks to 19°, that of the water does not fall below 40°. On the laud, the 

 whole amount of heat absorbed is accumulated within 50 or GO feet of the sur- 

 face; while on the lake, the agitation of the water tends to distribute the 

 summer accumulation through a depth of 900 feet. The average temperature, 

 and therefore the surface temperature, is lower than the surface temperature 

 of the land, and must, consequently, during the warm season, exert a cooling 

 influence. On the contrary, during the winter, the average temperature of the 

 water, and therefore its surface temperature, is much above that of the land, 

 and must, consequently, exert a warming influence on the contiguous regions. 



* Patent Office Report for 1S56. Agriculture, Plate iv. 



t Army Meteorological Register, 1855. It is impossible to overestimate our obligations to the 

 army officers who planned and executed the extended series of observations taken at the military 

 posts of the United States. 



X 18,536,038,400,000 cubic yards. 



