36 



GEOLOGICAL SURVEY OF WISCONSIN. 



rivers, springs and wells. The underground rivers reaching from tho 

 Eocky mountains, or the highlands of Dakota, exist only in the im- 

 agination. Heavy or continuous rains cause the water to rise in the 

 non-flowing artesian wells, in the same manner and for the same rea- 

 son that the water in lakes, rivers and ordinary wells rise under the 

 same circumstances. In dry weather, or during continued cold 

 weather, when the falling water ceases to penetrate the soil, the re- 

 verse takes place, the waters of lakes, rivers and non-flowing artesian 

 wells fall below their average height. Springs are subject to the 

 same variation to a considerable degree; it is only those that have 

 their sources at considerable distances that show but little or no vari- 

 ation during the changing seasons. 



The mean monthly and annual amount of rain- fall, at any given 

 locality is, therefore, an item of great importance that will often be 

 needed in the prosecution of the survey, and hence I contribute the 

 following table, the result of many years of patient labor. It A^nll 

 thus be made accessible to engineers, agriculturists and meteorolo- 

 gists, who will often have occasion to use it. 



The table shows the monthly and yearly amount of rain and melted 

 snow at Milwaukee, latitude 43° 3' JST., longitude 87° 66' W. The 

 observations for the years 1843-48 were made by E. S. Marsh, M. D.; 

 for 1855-59 and for 1872-73, by Mr. Charles Winkler; for all the 

 other years by I. A. Lapham. 



TABLE OP RAIN-FALL AT MILWAUKEE. 



