OF ATMOSPHERICAL TEMPERATURE. 139 



softening the rigour of climate. Wet tenaeious soils 

 are found the most difficult to heat or to drain, and 

 they will, therefore, be the most unfavourable to the 

 operations of the gardener ; extremely light sandy 

 soils, on the other hand, part with their moisture so 

 rapidly, and absorb so much heat, that they are 

 equally unfavourable ; and it is the light loamy soils, 

 which are intermediate between the two extremes, 

 that, as is well known, form the best soil for a gar- 

 den. Situation is, however, of much more conse- 

 quence than soil, for the latter may bs changed or 

 improved, but a bad (that is, cold) situation is incur- 

 able. Cold air is heavier than warm air, and, conse- 

 quently, the stratum of the atmosphere next the soil 

 will be in general colder, than those above it. When, 

 therefore, a garden is placed upon the level ground of 

 the bottom of a valley, whatever cold air is formed upon 

 its surface remains there, and surrounds the herbage ; 

 and, moreover, the cold air that is formed upon the 

 sides of low hills rolls down into the valley as quick- 

 ly as it is formed. Hence the fact which to many 

 seems surprising, that what are called sheltered places 

 are, in spring and autumn, the coldest. We all know 

 that the Dahlias, Potatoes, and Kidneybeans of the 

 sheltered gardens in the valley of the Thames, are 

 killed in the autumn by frosts whose effects are un- 

 felt on the low hills of Surrey and Middlesex.* Mr. 



* [A contrary effect is experienced in the valleys of our large 

 rivers and lakes in the United States. On the banks of the Hudson 

 a margin of land from half a mile to a mile in width on each side ie 

 very effectually protected from the late spring and early autumnal 



