84 PHYSICS. 
inner surface is attached a small bone, forming one of a connected series of 
four—the malleus, the incus, the os orbiculare, and the stapes. The aerial 
undulations are transmitted from the tympanum, by means of this series of 
bones, to two openings, the fenestra ovalis and the fenestra rotunda, 
in the labyrinth. This consists of several long excavations filled with 
a fluid in which the auditory nerve is expanded, passing in very fine 
ramifications into the cochlea. These various parts will be found 
represented in the anatomical portion of the work, to which we refer 
our readers. ner 
The precise function of the individual parts of the ear is not so well 
established as in the case of the larynx. The tympanum, however, serves 
essentially in hearing by its greater or less tension, and upon its sound con- 
dition depends, to a considerable extent, the excellence of hearing. The 
application of the hearing tube ( pl. 19, fig. 94) gives a proof of this, for in 
its employment the hearing is better when the sound waves received in 
the funnel, cc’, are concentrated in the tube ¢t’, and by means of the aper- 
ture mm’ are conducted towards the tympanum. By this means the latter 
is set into more vigorous vibrations, and the tone strengthened without the 
internal portion of the ear being directly affected. 
PYRONOMICS ; OR, THE SCIENCE OF HEAT. 
a. Expansion of Bodies by Heat, 
Our knowledge of heat is limited almost entirely to its effects; of its true 
nature we know almost nothing. It cannot lie concealed in the interior of 
bodies, as in this case the refinements of modern chemical analysis would 
obtain some indications of its presence. 
The term heat, then, is to be understood as expressing an effect ; when 
it has reference to a cause, it will be readily intelligible from the context. 
One of the most remarkable properties of heat is, that it expands all 
bodies; this expansion, as a general rule, increasing with the increment of 
heat. It is greatest in elastic fluids or gases, and least in solids. 
As all bodies are expanded by heat, the amount of expansion of a body 
-may serve to measure the degree of its heat. For a moderate range of 
temperature, the expansion of liquids is employed ; for very elevated points, 
however, the extension of a solid must be substituted. Heat measures of 
the first kind are called Thermometers ; of the second, Pyrometers. 
If a glass tube with a bulb at one end be partly filled with a liquid, and 
if the upper part of the tube be melted together, after a vacuum has been 
formed in the portion not occupied by the liquid, then, by heating the ball 
the liquid will expand, and will rise in the tube without obstruction, owing 
to the vacuum above. If now the tube be graduated to a certain number 
of equal parts, the proportional elevation of temperature can, in every case, 
be determined. For filling the tube either colored alcohol or mercury may 
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