“[T]he atoms or elementary particles themselves are not real; they form a world of potentialities or possibilities rather than one of things or facts.”

Physics and Philosophy (1958)
Context: But the resemblance of the modern views to those of Plato and the Pythagoreans can be carried somewhat further. The elementary particles in Plato's Timaeus are finally not substance but mathematical forms. "All things are numbers" is a sentence attributed to Pythagoras. The only mathematical forms available at that time were such geometric forms as the regular solids or the triangles which form their surface. In modern quantum theory there can be no doubt that the elementary particles will finally also be mathematical forms but of a much more complicated nature.

Physics and Philosophy (1958)
Context: The equation of motion holds at all times, it is in this sense eternal, whereas the geometrical forms, like the orbits, are changing. Therefore, the mathematical forms that represent the elementary particles will be solutions of some eternal law of motion for matter. Actually this is a problem which has not yet been solved.<!-- p. 72

Introductory
The Grammar of Science (1900)

Source: De architectura (The Ten Books On Architecture) (~ 15BC), Book II, Chapter I, Sec. 9
Context: There is no kind of material, no body, and no thing that can be produced or conceived of, which is not made up of elementary particles; and nature does not admit of a truthful exploration in accordance with the doctrines of the physicists without an accurate demonstration of the primary causes of things, showing how and why they are as they are.

"On the Atomic Theory," J. Chem. Soc., 2nd Ser., 1869, 7:328-365, on p. 365.

"Elementary particles and the laws of Physics" in The 1986 Dirac Memorial Lectures (1987)

Source: A New System of Chemical Philosophy (1808), Ch. III. On Chemical Synthesis

Source: The Turning Point (1982), p. 82.
Source: The Tao of Physics: An Exploration of the Parallels between Modern Physics and Eastern Mysticism
Context: At the subatomic level, matter does not exist with certainty at definite places, but rather shows "tendencies to exist," and atomic events do not occur with certainty at definite times and in definite ways, but rather show "tendencies to occur."

Preface
The Origin of the Universe (1997)