THE IMPORTANCE OF SHELTER. 389 



Western Atlantic, the waters of the gulf charging it in the transit, to the point 

 of saturation, with the moisture which its high temperature enables it so 

 copiously to receive, and which, in the process of cooling, is as freely precipi- 

 tated in passing up the great valley of the Mississippi, and over the almost im- 

 perceptible height of land into and down the valley of the great lakes, yielding 

 its last tribute of moisture to the mountains of Eastern New York and New 

 England. Fortunate indeed is it for the great West, with its teeming millions 

 of population, that a wise Providence saw fit to open to us so ample a gateway 

 to the gulf, through which we may woo these life-giving breezes ; else had these 

 broad valleys been, like the great central plateau of our continent, the home of 

 drought and hopeless desolation. 



Althougb, as has already been stated, the general theory of rainfall and the 

 causes of storms, whether of wind or rain, had been carefully studied by many 

 of the most capable minds, it was not till the invention of the 



MAGNETIC TELEGRAPH, 



and the wide extension of its lines permitted simultaneous reports from various 

 and widely separated points, nor yet until the establishment, under govern- 

 ment auspices, of a thorougli system of meteorological reports, from a widely 

 distributed corps of observers, had rendered practicable the collation of a system 

 of simultaneous observations from all parts of the country, that the true 

 theory of the formation of wind and rain storms came to be well understood. 



By means of such a system of reports we come to understand that our local 

 storms are generally, if not always, of the nature of whirlwinds of greater or 

 less magnitude; that when of small diameter the whirlwinds are often nearly 

 circular in form, but that extensive storms usually have a vortex greatly elon- 

 gated in one direction, generally north and south, or nearly so. 



It is also found true that such storms, besides their proper gyratory 

 motion, have more or less lateral motion, which, at least in the northwest, 

 is generally eastward or northeastward, and always in a direction nearly 

 at right angles with the longer diameter of the storm. Of course these 

 whirlwinds always originate at points where the lowest barometer indicates a 

 rarefaction and consequent rising of the air, and the winds setting toward 

 such point from all directions come to partake of the gyratory motion ; hence 

 the wind often, if not usually, blows from one direction, while the storm cloud 

 arises from another, and the wind usually changes at or near the close of the 

 storm, or in other words when the " storm centre" has passed the observer. 



These facts will also serve to explain how, in our State, these storms (which 

 always gyrate from west by south to the east, or in the direction opposite to 

 the motion of the hands of a watch) come from the west and yet are attended 

 by southerly or southeasterly winds, veering during or after the storm to the 

 southwest, and finally to the west and northwest. 



Although Michigan is doubtless quite as highly favored as most of the north- 

 western States, so far as amount and distribution of rainfall are concerned, all 

 will doubtless admit that her summer precipitation is usually by no means in 

 excess; and furthermore, that if timber growths exert a favorable influence, 

 either upon its amount or the equability of its distribution, we should by all 

 means adopt the most effective measures to preserve and even increase their 

 efiBciency in this respect. We will, of course, be reminded that the full realiza- 

 tion of such advantage is impracticable in a settled and cultivated country. 

 True, and yet judicious cultivators usually consider it essential to preserve a 



