Hi Pentcho,
Rather than haggle about the details of Carnot's argumentation, I'll give you a
better example of how science, proceeding in fits and starts, often stumbles
upon the "truth" through paths which are later recognized as insecure. I refer
to our discovery and development of the conservation of momentum. It was first
derived (and still is in textbooks) from Newton's laws of motion, a crucial
premise being the third law. With the discovery of the magnetic force between
moving charges, it was realized that there were forces that did not obey
Newton's third law. Surprisingly, this did not invalidate our conservation of
momentum conclusion - we merely raised it to the level of an a-priori
hypothesis, assigned the missing momentum to the electromagnetic field, and
produced a consistent and testable model of particle interactions.
Nature's pedagogy may at times lead us to useful conclusions through imperfect
premises. After we find the imperfections, we do the polishing; but we don't
through out a useful baby with the used bath water.
Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net http://www.velocity.net/~trebor
----- Original Message -----
From: "Pentcho Valev" <pvalev@BAS.BG>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, May 07, 2003 3:28 AM
Subject: Heat as an indestructible substance
| Bob Sciamanda wrote:
|
| > | In 1824, Carnot published essentially
| > | the following argument:
| > | Heat is an indestructible substance (calorique).
| > | Perpetuum mobile (of the first kind) is impossible.
| > | Therefore, all reversible machines working between two given
| > temperatures
| > | have the SAME efficiency. . . .- Pentcho
| >
| > Although heat as an indestructible substance was part of the "caloric
| > fluid theory", it is not crucial to the referenced Carnot argument.
|
| Carnot draws a straightforward analogy between a heat engine and a
| waterwheel so perhaps analysing the latter would make things clearer. The
| maximum efficiency of a waterwheel depends on the height of the waterfall
| only (this height is analogous to the temperature difference in the heat
| engine case). If two waterwheels working under the same waterfall had
| different efficiencies, they would be able to perform net lifting of water,
| in violation of the first law.
| The condition of indesrtuctibility of water is obviously crucial.
| Replace water with a liquid fuel - gasoline - and the conclusion that the
| efficiency depends on the height of the gasolinefall would become false.
| That is what happened in mid 19th century. Heat turned out to be fuel-like
| - underwent "destruction" in the heat engine and turned into work. Carnot
| conclusion (the original version of the second law) bacame just as false as
| the conclusion that the efficiency of a gasoline engine depends on the
| height of the gasolinefall. However Clausius and Kelvin quickly converted
| the failure into an indisputable foundation for the future theory.
|
| Pentcho