This is the sense of Lorentz’s hypothesis about the contraction of
electrons in case of motion. On the other hand, if we conceive the
second electron to be at rest, and therefore adopt the system (_x′_,
_t′_,) then the cross-section P′P′ of the strip of the electron parallel
to OC′ is to be regarded as its length and we shall find the first
electron shortened with reference to the second in the same proportion,
for it is,