" The very same effect is perceived when we look at objects
through spirits and water that are not perfectly mixed, or when we
view distant objects over a red hot poker or over a flame. In all
these cases the light suffers refraction in passing from a medium of
one density into a medium of a different density, and the refracted
rays are constantly changing their direction as the different currents
rise in succession. Analogous effects are produced when sound passes
through a mixed medium, whether it consists of two different mediums
or of one medium where portions of it have different densities. As
sound moves with different velocities through media of different
densities, the wave which produces the sound will be partly reflected
in passing from one medium to the other, and the direction of the
transmitted wave changed; and hence in passing through such media
different portions of the wave will reach the ear at different times,
and thus destroy the sharpness and distinctness of the sound. This
may be proved by many striking facts. If we put a bell in a receiver
containing a mixture of hydrogen gas and atmospheric air, the sound of
the bell can scarcely be heard.
Pages:
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59