Ill SITUATION AND SOIL 35 



Frost is seldom very severe in England at the sea- 

 side, but the salt spray and violent winds would 

 render such a place generally undesirable, though 

 good Eoses are grown in some seaside localities. 

 The old-fashioned saying is that " frost falls." This 

 is of course not true in itself, but it is true in effect. 

 Heated air, being lighter, ascends ; colder air, being 

 heavier, descends; and it is found that frost is 

 always most severe and dangerous in low-lying 

 places, and that a covering overhead is a better 

 protection than one at the side, because evaporation 

 upwards towards the sky produces cold. My neigh- 

 bour, a quarter of a mile off on a little hill, has 

 always from three to five degrees less of frost than I 

 have ; and even if it were not so I believe that the 

 same amount of frost would be more destructive to 

 vegetation to me in a river valley than it would be 

 to him on the upland. Valleys or low-lying ground, 

 especially if near water, should therefore be avoided, 

 and the uplands in all cases be preferred. 



Mere height above the sea-level would not, in 

 most cases, be a matter of much moment ; though 

 on the one hand the top of a mountain would not of 

 course be a desirable spot, and on the other a very 

 flat plain with little height above the sea would 

 probably be subject to severe frost ; thus the flats of 

 Cambridgeshire, which have such a slight fall to the 

 sea, are well known as registering very low degrees 

 of temperature. Eather high ground, not neces- 

 sarily the top of a hill, with valleys in the neigh- 

 bourhood for the cold air to fall to, would probably 

 be a good situation as to comparative immunity 

 from frost. In such a place the heavier or colder 

 air literally drains away to the valleys, which thus 



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