1 2 8 D O C . 1 5 C O M M E N T O N N O T E B Y G E H R C K E
Published in Deutsche Physikalische Gesellschaft. Verhandlungen 20 (1918): 261. Received 29 No-
vember 1918, published 30 December 1918.
[1]Gehrcke 1918. Two years earlier, Einstein had chosen not to respond to Gehrcke 1916 (see Ein-
stein to Wilhelm Wien, 17 October 1916 [Vol. 8, Doc. 267]). For further background, see the editorial
note, “Einstein’s Encounters with German Anti-Relativists,” pp. 102–104.
[2]Stokes 1845. For historical discussion, see, e.g., Whittaker 195153, Vol. I, pp. 386–387, and
Schaffner 1972, pp. 29–32.
[3]Drude 1912, pp. 470 ff.
[4]This inconsistency in Stokes’s theory of stellar aberration was first pointed out in Lorentz 1886,
secs. 4–6, and it was also mentioned in the discussion of Stokes’s theory in Lorentz 1909, secs. 147–
149. In Gehrcke 1918, the author referred to this discussion without giving any indication that Lorentz
concluded that Stokes’s theory in its original form is untenable. Lorentz did concede, however, that
the inconsistency in Stokes’s theory can be avoided by making suitable assumptions about the density
of the ether in the vicinity of matter, a suggestion made by Max Planck (see Lorentz 1899). Lorentz
was careful not to dismiss Planck’s suggestion out of hand, but made it clear that he considered it
highly implausible. Gehrcke, responding to Einstein’s assertions in Gehrcke 1919a, quoted a passage
from Drude 1912 to bolster his position, namely that the ether need not be completely free of vortices.
Still, even Gehrcke’s ally, Philipp Lenard, saw no way to salvage this approach (see Lenard 1921b,
p. 16). He introduced a “primal ether” (“Uräther”) to sidestep the difficulties.