I started reading through The Feynman Lectures and came across this diagram. What do the numbers next to the nodes in the diagram represent? It's not explained in the text. All that is mentioned is: "Figure 1–7 is an illustration of the three-dimensional structure of common salt, sodium chloride."

enter image description here

A direct link to the text is here, just Ctrl-F "crystal of salt".

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    $\begingroup$ Note that 1, 3, 5, and 7 are white circles, while 2, 4, 6, and 8 are black. $\endgroup$ – Jon Custer Jun 1 '16 at 18:09
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    $\begingroup$ Note also that they (the numbered nodes, I mean) represent the exact contents of one unit cell. Other than that, I don't think they have any meaning. $\endgroup$ – Ivan Neretin Jun 1 '16 at 18:14
  • $\begingroup$ The numbering most definitely does not define a unit cell. $\endgroup$ – MaxW Jun 1 '16 at 18:35
  • $\begingroup$ I never said it does. I said it represents the contents of one unit cell (in one of the possible ways), and I stand by that statement. $\endgroup$ – Ivan Neretin Jun 1 '16 at 18:43
  • $\begingroup$ I'm sure he wanted to explain something with the numbers, but later forgot to. What, I cannot fathom. The black and white circles each form a primitive tetrahedron. ?!? $\endgroup$ – Karl Jun 1 '16 at 19:55

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