The Meaning of Relativity / Four lectures delivered at Princeton University, May, 1921

by Albert Einstein

or

in which has been put

We must now note that equation (96) is valid for any system of co-ordinates. We have already specialized the system of co-ordinates in that we have chosen it so that within the region considered the

differ infinitely little from the constant values

. But this condition remains satisfied in any infinitesimal change of co-ordinates, so that there are still four conditions to which the