N<sub>A</sub>
Principles of Modern Chemistry (7th ed., 2012), Ch. 2 : Chemical Formulas, Equations, and Reaction Yields
“The definite mass ratios involved in reactions suggested a convenient method for counting the number of atoms of each element participating in the reaction. These results, summarized as the laws of chemical combination, provided overwhelming, if indirect, evidence for the existence of atoms and molecules.”
Principles of Modern Chemistry (7th ed., 2012), Ch. 1 : The Atom in Modern Chemistry
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David W. Oxtoby 13
President of Pomona college 1951Related quotes

A New System of Chemical Philosophy, Part I http://books.google.com/books?id=Wp7QAAAAMAAJ (1808) as quoted by Richard Reeves, A Force of Nature The Frontier Genius of Ernest Rutherford (2008)

Ничего нет, кроме атомов и их сочетаний. Нет атома, который периодически не принимал бы участия в жизни
from Новая этика (из монизма) http://tsiolkovsky.org/ru/kosmicheskaya-filosofiya/novaya-etika-iz-monizma/

“A diatomic molecule is a molecule with one atom too many.”
as quoted in [Dave DeMille, Diatomic molecules, a window onto fundamental physics, Physics Today, 2015, December, 34, 68, 12, 10.1063/PT.3.3020]
Introduction
Higher Mathematics for Chemical Students (1911)
Principles of Modern Chemistry (7th ed., 2012), Ch. 1 : The Atom in Modern Chemistry

Edwin Grant Conklin, in: Evolution by Association : A History of Symbiosis: A History of Symbiosis http://books.google.co.in/books?id=wEo1QUkr7pUC&pg=PA129, Oxford University Press, 22 August 1994