this conception was built the science of mechanics. The resulting
formulas sufficed for all motions of a slow nature; it was found,
however, that they would not conform to the rapid motions apparent
in electrodynamics.

"This led the Dutch professor, Lorentz, and myself to develop
the theory of special relativity. Briefly, it discards absolute
time and space and makes them in every instance relative to moving
systems. By this theory all phenomena in electrodynamics, as well as
mechanics, hitherto irreducible by the old formulae--and there are
multitudes--were satisfactorily explained.

"Till now it was believed that time and space existed by themselves,
even if there was nothing else--no sun, no earth, no stars--while
now we know that time and space are not the vessel for the universe,
but could not exist at all if there were no contents, namely, no sun,
earth and other celestial bodies.

"This special relativity, forming the first part of my theory,
relates to all systems moving with uniform motion; that is, moving
in a straight line with equal velocity.

"Gradually I was led to the idea, seeming a very paradox in science,
that it might apply equally to all moving systems, even of difform
motion, and thus I developed the conception of general relativity
which forms the second part of my theory."

As summarized by an American astronomer, Professor Henry Norris
Russell, of Princeton, in the Scientific American for November 29,
Einstein's contribution amounts to this: