D O C . 3 4 0 C O M M E N T O N F R I E D M A N N 2 7 1 . (14) For this calculation the second approximation given by (9a) does not suffice, how- ever in the expansion of (9), the terms in A and B of second degree must rather be taken into account. If one inserts this third approximation of function f in (14), then one obtains: .[8] The factor calculated for this special case is none other than the sought factor z in equation (1a), so we can summarize our result in the equation:[9] . . . . (1b) In a gas with heat flow, pressure forces do hence occur that, in the direction of the heat flow, try to dilate the gas and, crosswise to the heat flow, to contract it. The calculation shows that the magnitude of these forces of factor z comfortably allows for a test of the result by experiment.[10] A. Einstein. 340. “Comment on A. Friedmann’s Paper: ‘On the Curvature of Space’”(1) [1] [Einstein 1922p] Dated September 1922 Received 18 September 1922 Published 19 December 1922 In: Zeitschrift für Physik 11 (1922): 326. The results obtained in the cited paper regarding a nonstationary universe seemed suspect to me. In fact, it turns out that the solution given does not agree with the pxx mn ξ2fdτ = pyx mn ξη fdτ = etc. pxx pyy 9 50pRT ---------------fx2 - M 18 25pRT ---------------fx2 - M = [p. 3] fx2 pμν pδμν 9 50 ----- - 18 25pRT --------------- - M fμfν 1 2 --δμν - 2 += [p. 326]
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