RIVER SYSTEMS OF NEW HAMPSHIRE. 329 



southern states. Our chances of water dearth occasioned by summer 

 heat are thus greatly diminished as compared with other sections of the 

 country. 



Our winter temperature is more nearly like that of the same latitude 

 westward, being indeed less severe, the neighborhood of the sea having 

 the effect to lessen the extremes of our temperature, which is lower in 

 summer, and on an average for the year, but nearly the same in winter. 

 Our mean winter temperature, however, falls considerably below the 

 freezing point of water. The ground, therefore, with its contained water, 

 tends to freeze solid to a considerable depth, thereby lessening the supply 

 of streams. Much of the surface water upon the drainage sheds through- 

 out this season is changed to ice. The precipitation also is mainly in the 

 form of snow. But these circumstances, which seem to threaten water 

 dearth, never act to their full extent in combination to reduce river 

 supply. When a large depth of snow falls the ground does not freeze 

 deeply, and continues therefore to give forth the reserved abundance of 

 the autumn rains. Nor does the severity of the temperature often last 

 many weeks without such intervals as admit of rains and the thawing of 

 part of the accumulated snow, with sufficient time for drainage, by which 

 the water supply is reinforced and the lakes and reservoirs filled. Thus, 

 while our streams tend to run low in winter, they are still almost always 

 prevented from reaching so low a point as in the heat of summer.* 



The frequent thaws of winter also prevent the accumulation of snow 

 from being wholly reserved for the melting of spring. The disappearance 

 of the snow remaining at that season, however, sometimes attended with 

 heavy rains, usually produces the highest stage of water for the year. A 

 few of the conditions which modify this result deserve to be considered. 

 During the winter the snow generally becomes solidified, especially in its 

 lower portions, almost to ice, and in this form it disappears but slowly 

 before the advancing heat of the year. The ground, even if frozen before 

 snowfall, is usually thawed out beneath the snow of winter, and becomes 

 a reservoir for a large amount of water, thus retarding the discharge into 

 the rivers. For these reasons, the accumulations of winter go off with 



* Reference to charts illustrating isothermal lines and rainfall will show that the Merrimack valley is the 

 warmest area in the state, and, also, that it receives the most rain. Combining with these the constancy of flow 

 caused by the large lake reservoirs, and it is clear that the Merrimack river is superior to the Connecticut, if not 

 to any stream in the country, for its capabilities for driving machinery. C. H. H. 



VOL. I. 44 



