230 THE PRINCIPLES OF HANDLING WOODLANDS 



steepness of the slope. After passing the crest, a fire 

 travels more slowly in its descent on the other side. 



Mechanical obstructions, such as abrupt walls, narrow 

 ridges, outcropping ledges, and so on, tend to check a 

 fire and to prevent its gathering volume. On extensive 

 level ground, fires burn more uniformly, gather a greater 

 volume, generally do more damage, and extend over a 

 larger area than in rugged topography. 



Character of the Soil. Any influence which tends to 

 dryness increases the intensity of a fire. Thus on sand 

 and limestone soils, which warm up and dry out readily, 

 fires are likely to be very severe. Southern and western 

 slopes are apt to be more severely burned than others, 

 because they are the warm and dry exposures. 



Condition of the Atmosphere. The character of a 

 fire is influenced, further, by the condition of the atmos- 

 phere. Roughly, the greater the velocity of the wind, 

 the more rapid is the progress of the fire. A fire burns 

 more severely when the wind is constant than when it is 

 gusty. It is the steady high wind which makes the most 

 intense fire. 



A fire burns most fiercely when the atmosphere is 

 dry. Fires are, therefore, most severe during the hot 

 part of the day, and when fanned by a dry wind. A 

 moist atmosphere retards a forest fire. The well-known 

 fact that the night is the best time to fight a fire is thus 

 explained; for at night there is usually little or no wind, 

 while the air is comparatively heavy and damp. 



Rapidity of Surface Fires. No reliable estimate of 



