3 4 8 D O C U M E N T 3 6 6 J A N U A R Y 1 9 2 9 366. To Cornel Lanczos [after 10 January 1929][1] Dear Mr. Lanczos, It is not correct that my surface relation is a result of the identity alone. It is a result of the fact that in the neighborhood of a material point, the field equations hold: From the identity it namely follows that my surface integral vanishes if and only if the field equations are satisfied in the neighborhood of the point considered. If one sets then the above identity is given by . This has as its result . And from that, however, it follows that (static case!) only then when the integration surface, i.e., (in the static case) outside the mass point . The above divergence identity by itself thus yields 367. Fragment of Comment on Doc. 365 [Berlin, after 10 January 1929][1] [Not selected for translation.] W h ,i ( W h i ) 0 – W h i i –T = H i h H h ,i – t i = x T i t i + 0 t i + Ti df 0 = t i df 0 = T i 0 =