o 



1 8 The J ournal of Forestry. 



chains, and is further modified by the nature of the soil, the presence 

 of lakes, large rivers, or other sheets of surface water, and of forests. 



"The climate of mountains is subject to the same modifying causes, 

 with the additional iniluence of aspect. 



" Elevation chiefly affects]temperature, but as one gets higher the air 

 generally becomes drier as well as cooler, and winds are naturally 

 more violent, 



"The effect of elevation is seen in the forest vegetation, which, 

 vigorous in the plains, is less active on the hill-slopes, becomes 

 sluggish and dwarfed, until on high, unsheltered plateaux it even 

 disappears altogether. 



" Besides increasing the atmospheric humidity, and consequently 

 the rainM], 2'>roxim it jj to the mr exposes a place to the full violence of 

 the wind. So also one of the chief influences of neighbouring 

 'iiiountain-cluiins is to break the force of the winds. 



" The nature rf the soil affects the humidity of the climate in propoi- 

 tion to its compactness; the more compact a soil is, the less 

 hygroscopic it will be ; that is, the less water will it absorb or 

 retain. Secondly, the colour of the soil renders it more or less capable 

 of absorbing heat ; thus a dark soil will absorb more and reflect less 

 heat than a light-coloured one, and will thus in itself be warmer, but 

 will render the surrounding air cooler. 



"Surface vater (i.) by its evaporation makes the air moist and (ii.) 

 lowers the summer temperature ; but (iii.) its vapour, in the furm of 

 fog, intercepts the sun's rays, and is therefore liable to bring on frost. 

 As, however, it is less rapidly affected by changes of temperature than 

 the air, it may (iv.), by cooling more slowly than the air, diminish the 

 cold in the beginning of winter, but will similarly (v.) diminish the 

 heat in spring, (vi.) Sixthly and lastly, it offers no obstacle to the wind, 



"Forests (i.) by their shelter prevent evaporation; but the watery 

 vapour exhaled by their foliage more than counteracts this, lowering 

 the temperature in spring and summer, the growing season, (ii.) In 

 winter they present an obstacle to the radiation of terrestrial heat 

 thus diminishing the cold, so that (iii.) their general effect on tem- 

 perature is to prevent or lessen sudden changes. Wooded districts 

 (iv.) have more frequent if not more rain than other places, and the 

 forests act (v. as a barrier against wind. 



" Aspects are grouped as four, according to Mdiat are known as the 

 * cardinal ' points of the compass, which we will consider separately 

 and apart from such local modifying conditions as those of steep 

 valleys, extreme elevations, and sheltered localities. 



"A northern aspect receives no sun ; the heat is, therefore, feeble, and 

 the light diffused ; the winds are cold, contain but little moisture, 

 and are never strong. The temperature, however, being low, the 



