158 TEEES AS SHELTEE TO GEOUND TO THE LEEWAED. 



and moves only as local changes of temperature affect tlie specific 

 gravity of its particles. Hence there is often a dead calm in the 

 woods when a furious blast is raging in the open country at a few 

 yards' distance. The denser the forest — as, for example, where 

 it consists of spike-leaved trees, or is thickly intermixed with 

 them — ^the more obvious is its effect, and no one can have passed 

 from the field to the wood in cold, windy weather, without hav- 

 ing remarked it.* 



' * As a familiar illustration of the influence of the forest in checking the 

 movement of winds, I may mention the well-known fact, that the sensible 

 cold is never extreme in thick woods, where the motion of the air is little felt. 

 The lumbermen in Canada and the Northern United States labor in the woods, 

 without inconvenience, when the mercury stands many degrees below the 

 zero of Fahrenheit, while in the open grounds, with only a moderate breeze, 

 the same temperature is almost insupportable. The engineers and firemen of 

 locomotives, employed on railways running through forests of any consider- 

 able extent, observe that, in very cold weather, it is much easier to keep up 

 the steam while the engine is passing through the woods than in the open 

 ground. As soon as the train emerges from the shelter of the trees the 

 steam-gauge falls, and the stoker is obliged to throw in a liberal supply of 

 fuel to bring it up again. 



Another less frequently noticed fact, due, no doubt, in a great measxire to 

 the immobility of the air, is that sounds are transmitted to incredible distances 

 in the imbroken forest. Many instances of this have fallen under my own 

 observation, and others, yet more striking, have been related to me by credible 

 and competent witnesses familiar with a more primitive condition of the 

 Anglo-American world. An acute observer of natural phenomena, whose child- 

 hood and youth were spent in the interior of one of the newer New England 

 States, has often told me that when he established his home in the forest, he 

 always distinctly heard, in still weather, the plash of horses' feet when they 

 forded a small brook nearly seven-eighths of a mile from his house, though a 

 portion of the wood that intervened consisted of a ridge seventy or eighty 

 feet higher than either the house or the ford. 



I have no doubt that, in such cases, the stillness of the air is the most im- 

 portant element in the extraordinary transmissibility of sound ; but it must 

 be admitted that the absence of the multiplied and confused noises, which ac- 

 company human industry in countries thickly peopled by man, contributes to 

 the same result. We become, by habit, almost insensible to the familiar and 

 never-resting voices of civilization in cities and towns ; but the indistinguish- 

 able drone, which sometimes escapes even the ear of him who listens for it, 

 deadens and often quite obstructs the transmission of soimds which would 

 otherwise be clearly audible. An observer, who wishes to appreciate that 

 hum of civic life which he can not analyze, will find an excellent opportunity 



