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SOUNDS At NIeRT.-Every person must have


bserved that sounds such that OF falling water,
&c. which arc faisily or not at all heard during


ne day-tme, are distinctly audible ut night, even
when the direction and force of the wind and every


,bar general circumstance is the same. This Gu.
eious fact was remarked even by the ancients. In
arse cities, or in their ncighbo,nood, the increase
% The disiinctness of sound has been ascribed 10
The cessation of The powers OF animated beings,
such as men insects and birds and also to the


,a,ion of the actian OF winds apou The leaves OF
cees When the celebrated traveller, Baron Hum
pod, Ers; heard the noise of the great catarac,s OF
he Oronoco. in the plain whics surrounds the mis-
sion of the Apures, his attention was particularly
:aled to this curiors fact, and he was OF opinion
,hs, the noise was three times greater in the nigh
than in the day. The usual explanation of the
phenomena was suite insufficient in this case, as
the humH,ing OF insects much greater in the
nigh, than in the day, and the breeze which might
have aci,a,ed the leaves of trees never rose Till
AFTER sunset, Humboldt was led therefore to as
cribe The dninution of soand during the dag 10 the
presence of the sun, which Influences the propa
CATION and iatensity of sound, By opposing TO them
currents of air of different density, and partial un
.iula,ioas OF the atmosphere produced by the heat
ing of the different parts of the ground. In these
cases wave of sound, when i, meets two portions
of air OF different density, is divided into two or
more waves. part of the primitive wave being
propaga,ca with more rapidity Though The denser
portions than the parts that pass through air of less
density. In THIS way the wave is broken downin-
two different parts, which arrive at the ear at
different times Ehe different portioss of the wave


passing sgain through succeeding portions of the
atmosphere Of different density, may DE SO wasted
and fritsered down to be incapable Of affecting
the ,ympaaam. Edinburgh Encyclopedia.