220 On the Construction of Buildings 
ces, the sound will either be greatly diminished or entirely 
destroyed. As an analogous illustration of this, witness the dif 
ficulty with which light is transmitted through a glass filled with 
cracks, imperfections and impurities. 
So, also, when the medium is a mixture of gases, vapors oF 
liquids, ora combination of the one with the other, the effect, 
on both the velocity and intensity of the sound, is still more 
striking. Mr. Leslie found by experiment that, when the air of 
a receiver was only half exhausted and the deficiency supplied 
with hydrogen gas, the sound of an enclosed bell was thereby 
diminished so as to become scarcely audible. Recognizing, 
again, the analogy of light and sound, in this respect, Herschel 
thus illnstrates its imperfect transmission through a mixture of 
ilerent densities. 
When the light passes from a portion of the water to the brandy, of 
from the brandy to the water, a part of it suffers reflection, and as the 
the light will also suffer refraction. ow, a s must take place 
many hundred times while the light is passing through a large glass 
e 
of these imperfectly blended liquids, it is not difficult to unders 
how we are unable to see objects distinctly through the mixture. With 
sound the effect is precisely the same, but if the two media are of very 
different characters, the one a gas and the other a fluid, as in the oa 
of falling rain, or the one a gas and the other a solid, as in the cas® d 
falling or newly fallen snow, the scattering and deadening of the sour 
is still more complete.” 
: tet ee ae 
The effects here produced are attributed, as in solids, oar | 
of homogeneity in the medium or substance through whien a 
sound is passed. ‘The explanation given by Mr. Herschel 3s ® 
follows: : 
- The sonorous pulses, in their passage through the wnat 
every instant, changing their medium. Now at every chan 
ys 
Sieur é : dt 
the direction of propagation of the transmitted part is changed, rect 
tude of no” 
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interfering with each other in all directions. Now, Vv toes eX 
lace, a mutual destruction of the waves, to a greater oF - which 
arises, and the sound is stifled or obstructed. But of all ae tk 
obstruct the propagation of sound, one of the most effective |” 4 
want of perfect adhesion at the juncture of the pars, f 
nedium consists. The effect of this may be conceived, — 
the superficial strata of molecules of each medium when ! 
