288 BOARD OF AGRICULTURE. [Jan., 



sas. Connecticut has 216 large enough to be represented on a 

 map of the same scale. Within a radius of 25 miles from 

 Boston there are 180. Minnesota has 476 on the Century- 

 map, and Maine, New York, Canada, Michigan, Wisconsin 

 number their lakes by the thousands. In fact the connection 

 between the origin of lakes and the former presence of the ice 

 is so close that the southern extension of the ice lobes could be 

 roughly determined by mapping the lakes. 



Ground Water. The water which falls as rain upon the 

 earth is divided into three parts — that which is evaporated, 

 that which finds its way directly into the streams and forms 

 rivers and lakes, and that which enters the ground, to remain 

 there for a longer or shorter period of time. The fluctuation 

 in level of lakes and streams shows clearly the relation of the 

 water bodies to rainfall. The amount of water in the ground 

 is likewise intimately connected with the rainfall. In dry 

 weather the water in wells sinks and in droughts may entirely 

 disappear. Springs are strong flowing, or intermittent, or 

 cease altogether in accordance with the variation in climate. 

 The amount of ground water depends chiefly, therefore, upon 

 the amount of rainfall, which averages between 2 inches and 

 600 inches a year. Connecticut receives between 40 and 50 

 inches per year. 



The amount of water which enters the ground is dependent 

 somewhat upon the character of the topography and the tex- 

 ture of the soil. If the rain falls gently more goes into the 

 ground ; sometimes all of it enters. If the surface of a coun- 

 try is flat it will evidently take in more rain than if hilly, and if 

 the soil is loose and open it will receive more rain than if dense. 



Taking the earth as a whole 22 per cent, of all the rain that 

 falls enters the rivers, and the remaining 78 per cent, is divided 

 between that which is evaporated and that which enters the 

 ground. Certain rivers of New South Wales take only 2>4 

 per cent, of the precipitation ; some New England streams carry 

 over 50 per cent. The amount evaporated is relatively small 

 and the total amount of ground water is great and varies with 

 the porosity of the rocks and the soil. When marbles of uni- 

 form size are placed together it is found that the pore space 

 equals 32 per cent, to 40 per cent, of the solid parts. Theo- 

 retically, when the spheres are as compact as possible there is a 

 minimum porosity of 25.95 P^^ cent, and when loosely packed 



