Several themes were covered in this book that later became part of the theories of Einstein and other scientists, such as: "Introductory - The Scope and Method of Science" "The Facts of Science" "The Scientific Law" "Cause and Effect - Probability" "Contingency and Correlation - The Insufficiency of Causation" "Space and Time" "The Geometry of Motion" "Matter" The notion of matter is found to be equally obscure whether we seek for definition in the writings of physicists or of "common sense" philosophers.
The others are unintelligible, because we find that matter, force, and "action at a distance" are not terms which express real problems of the phenomenal world.
The customary definitions of mass and force, as well as the Newtonian statement of the laws of motion, are shown to abound in metaphysical obscurities.
It is also questionable whether the principles involved in the current statements as to the superposition and combination of forces are scientifically correct when applied to atoms and molecules.
The hope for future progress lies in clearer conceptions of the nature of ether and of the structure of gross "matter."
But there are outstanding difficulties, notably that gravitation has so far defied all efforts to bring it into line with this scheme, and that no simple concept has yet been furnished to represent the positive electricity of experiment.
The constancy of the mass of a body in material dynamics, which is the whole experimental basis of that science, is replaced by the conception of all electrons of the same type (negative, possibly also positive) being identical in character.