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112 334 Die absolute (thermodynamische) Tetnperaturscale.
I j)dv -}- yn — j)'u
Von diesem Betrage ziehen wir die bei der (isothermisclien)
Gasausdehnung verschluckte Wärme ab, welche nach Gleichung
3 ist
5. Nach den Versuchen findet nun eine geringe Abkühlung
des Gases um C statt. Ist K die Wärniecapacität des Gases
welches in der Zeiteinheit durch den Pfropf tritt, so ist
— Kd =
oder kürzer
pdv -{-pu —
]j u — p'u'
u
fi dt '
Hiernach ist also die durch die äussern Arbeiten erzeugte
Wärme nicht ganz zureichend um die bei der Gasausdehnung
verschluckte Wärme zu decken. Dies deutet auf einen Wärmeverbrauch
durch innere Arbeit.^)
„Let air be forced continuously and as uniformly as possible, by
uieans of a forcing pump, through a long tube, open to the atmosphere at
the far eiid, and nearly stopped in one place so as to leave, for a short space,
only an extremely narrow passage, on eacli side ofwhich, and in every otber
part of the tube, the passage is comparatively wide; and let us suppose, first,
that the air in rushing through the narrow passage is not allowed to gain
auy heat from, nor (if it had any tendency to do so) to part with any to, the
surrounding matter. Then, if Mayer's liypothesis were true, the air after
leaving the narrow passage would have exactly the same temperature as it
had before reaching it. If, on the contrary, the air experiences either a cooling
or a heating effect in the circumstances. we may infer that the heat
produced by the fluid friction in the rapids, or, which is the same, the thermal
equivalent of the work done by the air in expanding from its state of
high pressure on one side of the narrow passage to the state of atmospheric
pressure which is has after passing the rapids, is in one case less, and in
the other more, than sufficient to compensate the cold due to the expansion;
and the liypothesis in question would le disproved." Joule's Papers IL
p. 217 u. f. f.
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