20 THE UTILITY OF FORESTS. 



have reached some size, however, even forests will not stop 

 them. 



(d) Protection against Air Currents. — Forests break or moderate 

 the force of air currents and in this way afford protection to lands 

 lying beyond them against cold or dry winds. They also afford 

 shelter to cattle, game and useful birds. Their importance in this 

 respect should not be overlooked. The presence of birds, the 

 great enemies of injurious insects, depends often on that of wood- 

 lands, though in this respect hedgerow trees are equally, or even 

 more, effective. 



(e) Aeration of the Soil. — This is a large subject which cannot be 

 dealt with in this place ; but it should be mentioned that the 

 action of the root system of trees takes part in enabling air and 

 water to penetrate into the soil, more particularly in the case of 

 binding soils and subsoils. 



4. Influence upon Hygiene, iEsTHExics and Ethics. 



Forests, as part of the vegetation of the earth, take their share 

 in keeping a proper balance of carbon dioxide in the atmosphere ; 

 they dissect it, keeping the carbon and setting free oxygen ; the 

 process is reversed when wood is burnt or decays. 



Observations appear to show that forest air, hke sea air, is much 

 richer in ozone than air in the open country and especially in 

 towns. Ebermayer, who made extensive observations, found 

 up to five times as much ozone in the forest as in the manu- 

 facturing town of Zwickau. He found the greatest difference 

 during winter, which seems to show that the presence of ozone 

 does not depend on the action of the leaves. French investi- 

 gators have further ascertained that the number of bacteria in 

 forest air is only a fraction of that found in Paris air. 



Based on observations of these kinds it has been asserted that 

 forests have a considerable influence in counteracting disease. 

 Instances are not wanting where forests are said to have given 

 protection against the germs of malaria, but there are others in 

 which they are believed to have had the opposite effect. However 

 that may be, the author is inclined to think that any beneficial 

 effect of forest air is chiefly due to the absence of smoke, dust and 

 injurious gasses and, above all, to the greater tranquillity of the 

 human mind, free from worry while in rural parts of the country. 



