XLIV
e) It is strengthened by the neighbourhood of a sounding
body 253. (Resonance of air).
§ 101. The Velocity of sound in air, 248. (1,100 ft. a se
cond). Gay, Lussac, and Alex. v. Humboldt 1822.
§ 102. The Propagation and Velocity of sound in liquids
and solids. 250. In general liquids conduct sound better than
solids (Biot, Gay, Lussac, Sturm and Colladon). The velocity of
sound differs with different mediums, e.g.
in whale-bone 6 ⅔ times
" linden-wood 15 "
" glass 16⅔ "
" iron 16⅔ "
" fir-wood 18 "
greater than in the air.
§ 103. Velocity rises also in one and the same body, if the
condition of that body changes (f. e. different trunks of one kind
of wood and higher temperature increase velocity of sound, mois
ture in the air hinders the propagation of sound). Velocity of
sound is quite independent of the source of sound and its height
or depth (a concert at some distance).
§ 104. Reflection of sound or echoes. 251. The reflec
tion of sound takes place according to the same laws as the re
flection of heat and light. Place 2 parabolic mirrors at some
distance from each other; at a certain point we put a watch in
front of the one, called the focus. All the vibrations emanating
from this focus will be reflected from this mirror in parallel rays,
fall on the second mirror and are thrown back to its focus. If
the ear is put to this second focus, the ticking of the watch is
distinctly heard, because all the sound-waves are concentrated
in the ear.
§ 105. Under what circumstances an echo will take place?
