🚀 go-pugleaf

In article <1992Dec13.195146.28828@u.washington.edu>, godden@stein.u.washington.edu (Jeff Godden) writes:
> 
> OK, that all makes sense, but when/who/how (particularly how) did grace
> us with 6.02e23?  How do you go about counting the number of carbon atoms
> in 12 grams?  Light scattering?  Osmotic theory?  Those all seem too 
> insensitive for the number of decimal points I've seen quoted.
> 
 Perrin measured the diffusion coefficient of Brownian particles and applied
 the Stokes-Einstein equation. This isn't very precise since, among other
 things, it assumes that the Brownian particle is a sphere - but it did get
 him a Nobel Prize in 1926.

 Nowadays the way to go is to measure the masses of individual atoms (or
 rather, ions) in ion traps. (Measure the frequency and radius of cyclotron
 motion). The precision of such measurements is fantastic - people are
 seriously talking about measuring the relativistic mass difference associated
 with electronic excited states of atoms.