684 STATE BOARD OF AGRICULTURE. 



currents of air which are forced to rise up the slope, expand and cool 

 as tliey rise, thereby producing greater condensation and precipitation. 

 It will be noted later that the effect of elevation on rainfall is notice- 

 able even in Michigan where the differences in height above sea level 

 are com])aratively slight. 



The tliird factor in the control of climate, that of environmental con- 

 ditions, is one wliich is particularly important in Michigan. The effect 

 of the Great Lakes is marked, especially along Lakes Michigan and 

 Superior, causing wide departures in temperature and other climatic 

 conditions, between those sections and other regions of the same latitude 

 and altitude. Large bodies of water heat much more slowly in summer 

 and cool correspondingly slower in winter, than adjoining land areas, so 

 that the Great Lakes are cool in summer and warm in winter, compared 

 with the temperature of interior land areas. This is due to the fact that 

 from five to seven times the amount of heat necessary to raise the tem- 

 perature of a given weight of soil one degree is required to warm the 

 same weight of water an equal amount. The fact that considerable heat 

 from the sun's rays is used up in evaporating some of the surface water 

 also retards rapid heating. Water is usually in motion and any heating 

 at the surface is transferred to other regions, whereas in the case of 

 the soil this mixing does not take place and the surface becomes super- 

 heated, and this is another reason why the soil is warmer than water 

 areas in summer. Furthermore insolation is transmitted and conducted 

 through Avater mucli more readil}" than through soil, whicli is an addi- 

 tional cause of super-heating of the surface of latter compared to the 

 former. As a result of these various factors actual tests of temperature 

 of the water in the Great Lakes in mid-summer show readings as much 

 as 30° F. to 40° F. lower than soil temperatures taken near the surface 

 of the ground in the interior of the state at the same time. The pre- 

 vailing westerly winds blowing across these wide expanses of compara- 

 tively cool water in summer are greatly reduced in temperature and 

 reach the Michigan shore as cool, refreshing breezes. 



The great volume of heat that is stored up in the lakes during the 

 summer is held well into the winter season. In fact only in the very 

 coldest winters does the water freeze solidly across, and then only for 

 short periods. Therefore the extremely cold northwest winds which 

 usher in tj^pical cold waves in winter, are decidedly tempered in cross- 

 ing the comparatively warm w^ater and strike the eastern and southern 

 coasts much moderated in temperature. 



The fourth factor influencing climate is the location of the region 

 relative to the normal storm path. Storms are areas of low atmospheric 

 pressure which travel across the continents and oceans in a general west 

 to east direction, sometimes retaining their identity clear around the 

 world. On account of the fact that the winds blow spirally inward 

 toward the center of these great low pressure areas, as they progress 

 eastward, they are called "Cyclones." They are great atmospheric 

 whirls, usually covering several states in extent, and travel easterly 

 from 200 to 2^000 miles per day. The paths or routes that these dis- 

 turbances travel are quite well defined. The majority of them move some- 

 what southeastward over the western half of the country, clmnging 

 their course to northeastward Avhen they reach a point a few hundred 

 miles this side of the Rockv Mountains. The further south a storm 



