Christoph Ballot

Christoph Buys-Ballot nsIn thermodynamics, Christoph Buys-Ballot (1817-1890), or Buys Ballot, was a Dutch meteorologist noted for his 1858 so-called dining room anecdote objection to Rudolf Clausius' calculation of the speed of gas molecules.

Overview
In 1858, Buys-Ballot objected to the calculation of the speeds of gas molecules by German physicist Rudolf Clausius, said to be several hundred meters per second on the grounds that it takes up to several dozen seconds for the aroma of a hot dinner to travel across a long dining room. [1] The specific now-famous ‘dining room anecdote’ objection by Ballot is: [2]

“If I were sitting at one end of a long dining room and a butler brought in dinner at the other end, it would be some moments before I could smell what I was about to eat. If atoms were flying at hundreds of meters per second, I should smell the dinner as soon as I saw it.”

This objection spurred Clausius into the development of the rebuttal that the reason smell takes so much longer to cross a room is that the particles of gas constantly bang into each other, hence the path of any one given molecule is zig-zaggy, the overall magnitude of the path traversed by the particle referred to as the ‘mean free path’; a term introduced the following year by Clausius to remedy Ballot’s objection. [3] Clausius’ short answer was that: [4]

“Those portions of a path of a molecule throughout which the molecular forces are of influence in sensibly altering the motion of the molecule, either in direction or velocity, must be of vanishing value compared with those portions of the path throughout which such forces may be considered as inactive.”

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Education
Ballot completed his BS in mathematics and physics in 1839 at Utrecht University. In 1842, he studied under chemist Gerrit Mulder and the following year published a book of tables for use in inorganic chemistry lab. In 1844, Ballot completed his PhD, with a thesis On Cohesion and Adhesion (The Synaphia et Prosaphia), under physics professor Richard Rees. At Utrecht University, he was professor of geology and mineralogy (1845), theoretical chemistry (1846), mathematics (1848), and physics (1867).

References
1. (a) Buys-Ballot, Christoph. (1858). “Ueber die Art von Bewegung welche wir Warme und Elektrizitat nennen” (“On the Kind of Motion we Call Heat and Electricity”), Ann. Phys. 103: 240.
(b) Clausius, Rudolf. (1857), "Über die Art der Bewegung, die wir Wärme nennen", Annalen der Physik, 100:353–379; trans. “On the Nature of the Motion which we call Heat” (PDF), Philosophical Magazine (1857), 14:108-27.
(c) Lindley, David. (2001). Boltzmann's Atom: the Great Debate that Launched a Revolution in Physics (pgs. 24-25). The Free Press.
2. Muller, Ingo. (2007). A History of Thermodynamics - the Doctrine of Energy and Entropy. New York: Springer.
3. Clausius, Rudolf. (1859) [1858]. “On the Mean length of the Paths described by the Separate Molecules of Gaseous Bodies on the Occurrence of the Molecular Motion: together with some other remarks upon the mechanical theory of heat”, Phil. Mag. 17:81-91.
4. Purrington, Robert D. (1997). Physics in the Nineteenth Century (pg. 138). Rutgers University Press.

Further reading
● Laidler, Keith. (1995). The World of Physical Chemistry (pgs. 146-47). Oxford University Press.

External links
C. H. D. Buys Ballot – Wikipedia.

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