Richmond enquirer. [volume] (Richmond, Va.) 1815-1867, 1821-12-15
[Humbolars Personal .Na7utire.
NOCTURNAL INCREASE OF SOUNDS


llun1oW endeaVors TO account for the increase of
s"''''s turing Inc night, from Observing that the
i.s."e' % inc sun Affects the propagation and in
iensiiy OF sound by the Obstacles nnnosed m s t,,
MISSION ny currents of air Of different densities and
Partial unduIaIonthe result of the uneo,nI hcatin,,
ol various parts otthe earths surface I'm air t rcst
"Ur,nfr ne dfy, or mixed with elastic vanours O.
q"'y distributed through it, the sonorous unspI,t,nr
IS propagaed without difficulty But WHOM liz a;,.
y crossed IN every direction hy small currents of a
"her temperature, tile sOnOroIs mntulaiion III, dcs
lNo Two waves, nj the spot where there is the mos,
scGdch Change IN the density of The medium u,us
producing partial echoes, Which weaken The hody az
H"u'" heciuse one Of the sonolous waves is reflect
efl back upon Itself The theory ofthese partitions Of
S"n"'ous waves has been explained by NJ Poisson
~ ~ not, therefore, the motion of the passorc cc ,
P1rucles ol airirom below upwards nor the s,,nll
o''Iue currents of this luid that we consider "a
aI 'S"'s, ny impulse, the propagation of the sono-
~ WIS; N0Ee or impulse impressed on tie
surace OF The liquid will form circles around fc i'm,
gNSN"S GENRE, even when the liquid is in agitation
3fNtIM kinls OF waves may cross in air, as well as
w water without interfering with each other Inn
INC rue cause OF the less intensity of sound i, : ,
.,a5 line appears TO he the want of honIorcneitv IN
lle elas'ic medium There is at this time a sudden
~ ueiSiy throughout, produced 10y small ear
I1i'S u NV, oil high temperature, rising from Dor
io"s o 'he earths surface that are lneuuay heated
I'e Sohoions waves are then divided in ihe same
"'9'"c' US luminous rays arc refracied, and form
',"pSt ol Souhd wherever strata of air of uucot,uI
density are contiguous. distinction mnst M, fer,
peWeeh nc intensity OF sound or of lrht and the H.
,eSW pi me sonorOus luminous wave When
tnese waves arc propelled across STRATA of d6nrcuf
hensies two Simultaneous effects will Inc nroI,red.
mere viii be clIange in the direction of the wave
pndeNtEcti0n OF lighter sound. The reflection tiu
"cc'UUn,pahicS each rciiacOn weakens the intensity
81 lght tte separation OF the sonorous wave causes
"Lml echoes, and tmt portion which returns ON it,
s'' becomes lnscnshio to our car, in weak noises
Nv 'tc Slo' "lnfc the density Of the medium Sudden
y changes In the niyeee with double images, that
"hGh mas Undergone rciractOn contiguous To the
"u ".'vays y"tker tlIan The direct image STA
ia Oh h"'ds, o very different density may so alter
nate, that tue primitive direction of The luminous or
INC S@O9rons ray VII remain the same but tic infcn.
si9 o. lpe ray will be not the less weakened on tla
account. Dsrng The night the surface OF die earth
c|ol'; tue parts covered with grass or with sand
,'Nc VIC sumo temperature the atmosphere is no
I""Sfr crossed ny currents Of not air. rising ouuciy
~ Nefleaiiy 10 every direction. The medium being
INV Deeome more Homogeneous. the sonorous wave
's'cs with less difficulty, and the intensity of sound
increases, as Tie separations OF tic sonorous waves
'"'e'"oes Docomeies fl equom. fNco IfoHiih .Mar.