^{page 31 note 1} When A and B have chosen clock-graduations for which the two f's are identical, they may be said to be provided with identical clocks.

^{page 31 note 2} What are usually called the “Lorentz formulae,” connecting A's and B's assignments of epochs and co-ordinates to any event whatever, can be shown to follow from the above formulae without further assumptions.

^{page 32 note 1} Statements sometimes made to the contrary, as for example that nebulae may ultimately possess velocities greater than that of light and so pass out of causal connection with the rest of the universe, are erroneous. The error came in owing to a false identification of “cosmic” time with the time of experience.

^{page 33 note 1} In most current presentations of relativistic cosmology this condition is not imposed, but is verified a posteriori. In my own presentation it is imposed a priori.