Page:Relativity (1931).djvu/165

$x'^{2}+y'^{2}+z'^{2}-c^{2}t'^{2}=x^{2}+y^{2}+z^{2}-c^{2}t^{2}$

(11a).

is satisfied identically. That is to say: If we substitute their expressions in $x$, $y$, $z$, $t$, in place of $x'$, $y'$, $z'$, $t'$, on the left-hand side, then the lefthand side of (11a) agrees with the right-hand side.