W. A. Norton—Molecular and Cosmical Physics. 13 
to the luminiferous ether. The collapse of an envelope is 
attended with vibratory movements of its individual atoms both 
toward and from the central nucleus, and at right angles to 
this line oy hia in rate with the position of the atom in the 
ich originate ethereal waves of diverse rates of 
Heat ; is eit by good aria te chiefly by waves of 
the electric ether passing over from molecular envelope to 
another; and hence the same pliynical: “oonititions which favor 
the conduction of heat should also favor the conduction of elec- 
tricity. Heat may also be slowly and imperfectly conducted 
by successive radiations from molecule to molecule through the 
a ether, with attendant absorptions by the molecular 
velopes ; when the density of the interstitial electric ether is 
£66 feeble to admit of direct conduction. 
20. What is called the interior ae energy of a body of 
matter, in the mechanical theory of heat, is the mechanical or 
equivalent thermal energy capable of Weihiy expended, or given 
out, in a contraction of the mass after expansion, or in the con- 
densation of simple into compound molecules, or in the collapse 
nded molecular envelo When the expansion of en- 
vate has resulted srecitinr wees from an increased attraction 
between contiguous molecular envelopes, superinduced by an 
extraneous action (awed ical or the rmal), t the potential heat- 
energy absorbed will be eben to the attractive energy ex- 
pended. The work done, if any, in this case by the extraneous 
action in opposition to molecular resistances is altogether dis- 
tinct from this incidental effect. The mechanical stretching of 
wires, and liquefaction, with me esa absorption of heat, 
may be cited as illustrative e 
e hypothesis now in vomue that heat imparts vibratory 
movements to the atoms themselves of bodies, involves the 
assumption that the vibrations are as rapid, or approximately so, 
as the undulations of the heat-waves; which the comparatively 
sl ’ transmission of sound- vibrations, and the com- 
paratively feeble intensities of the elastic forces called into play 
in their transmission, renders in the highest degree improbable. 
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