The greatest range of
temperature possible or conceivable is from the absolute temperature
of the substance at the commencement of the operation down to absolute
zero of temperature, and the fraction of this which can be utilized is
the ratio which the range of temperature through which the substance
is working bears to the absolute temperature at the commencement of
the action. If W = the greatest amount of effect to be expected, T and
_t_ the absolute temperatures, and H the total quantity of heat
(expressed in foot pounds or in water evaporated, as the case may be)
potential in the substance at the higher temperature, T, at the
beginning of the operation, then Carnot's law is expressed by the
equation:
/ T - t \
W = H( ------- )
\ T /
I will illustrate this important doctrine in the manner which Carnot
himself suggested.
[Illustration: THE GENERATION OF STEAM. Fig 2.]
Fig. 2 represents a hillside rising from the sea. Some distance up
there is a lake, L, fed by streams coming down from a still higher
level. Lower down on the slope is a millpond, P, the tail race from
which falls into the sea. At the millpond is established a factory,
the turbine driving which is supplied with water by a pipe descending
from the lake, L. Datum is the mean sea level; the level of the lake
is T, and of the millpond _t_. Q is the weight of water falling
through the turbine per minute.
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