INFLUENCE OF FOREST ON HUMIDITY. 
165 
The vegetable mould, resulting from the decomposition of 
leaves and of wood, carpets the ground with a spongy covering 
which obstructs the evaporation from the mineral earth below, 
drinks up the rains and melting snows that would otherwise 
to the immobility of the air, is, that sounds are transmitted to incredible 
distances in the unbroken 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 childhood and youth were spent in the interior of one 
of the newer New England States, has often told me that when he estab¬ 
lished 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 inter¬ 
vened 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 
important element in the extraordinary transmissibility of sound ; but it 
must be admitted that the absence of the multiplied and confused noises, 
which accompany 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 indistinguishable drone, which sometimes escapes even the ear of 
him who listens for it, deadens and often quite obstructs the transmission 
of sounds which would otherwise be clearly audible. An observer, who 
wishes to appreciate that hum of civic life which he cannot analyze, will 
find an excellent opportunity by placing himself on the hill of Capo di 
Monte at Naples, in the line of prolongation of the street called Spac- 
canapoli. 
It is probably to the stillness of which I have spoken, that we are to 
ascribe the transmission of sound to great distances at sea in calm weather. 
In June, 1853, I and my family were passengers on board a ship of war 
bound up the AEgean. On the evening of the 27th of that month, as we 
were discussing, at the tea table, some observations of Humboldt on this 
subject, the captain of the ship told us that he had once heard a single gun 
at sea at the distance of ninety nautical miles. The next morning, though 
a light breeze had sprung up from the north, the sea was of glassy smooth¬ 
ness when we went on deck. As we came up, an officer told us that he 
had heard a gun at sunrise, and the conversation of the previous evening 
suggested the inquiry whether it could have been fired from the combined 
French and English fleet then lying at Beshika Bay. Upon examination 
of our position we were found to have been, at sunrise, ninety sea miles 
