Note 101 — Chapter XXXI · THE SEPARATION OF SPACE-TIME INTO SPACE AND TIME IN A GRAVITATIONAL FIELD
Reading edition
In reality the identification is a little more complicated; it is given by
Furthermore, it can be seen that this potential , of varying value from place to place, is connected with the variable speed of light from place to place through the gravitational field. More precisely, the speed of light in vacuo is given by , which is approximately or , where is the mass of the body exciting the gravitational field.