4 8 D O C U M E N T 3 1 A P R I L 1 9 1 9
also
Dabei ist der Akkomodationskoeff. = 1
gesetzt.[7]
Falls Du diese Grundlage der Betrachtungen billigst, wäre Eppstein gerne bereit,
mir beim Weiterbauen auf derselben behilflich zu sein. Andernfalls wäre ich Dir
sehr dankbar, wenn Du uns Deine Auffassung der Sache vielleicht etwas deutlicher
mitteilen wolltest.
Inzwischen schaue ich mir die diesbezügliche Literatur etwas an. Ich wäre so
froh, wenn daraus etwas werden würde.
Sonst wenig Neues. Nur mussten Janka und ich leider unsere kleine Wohnung
verlassen[8]
(es wurde uns aus Spekulationszwecken gekündigt) und nun hause ich
einsam in einem kleinen Stübchen in der Sonneggstrasse. Ich werde demnächst an
Elsa schreiben. Inzwischen Grüsse Sie recht herzlich von mir, und ich danke Dir
von ganzem Herzen dass Du Dich meiner in der „Arbeitsnot“ angenommen hast!
Mit herzlichen Grüssen Deine
Edith.
Meine Adresse ist Sonneggstr. 70
ALS. [9 194].
[1]Edith Einstein (1888–1960) was a doctoral student in physics at the University of Zurich and a
first cousin.
[2]The reference to Buridan’s ass is occasionally also made by Albert Einstein (see Einstein to
Heinrich Zangger, 20 September 1911 [Vol. 5, Doc. 286]).
[3]Paul Epstein, her dissertation advisor.
[4]The radiometer, invented by William Crookes (1832–1919) (see Crookes 1875), is a device con-
sisting of vanes mounted on a spike and enclosed in a partly evacuated transparent container. The
vanes are silvered on one side and blackened on the other, and will begin spinning when illuminated.
The effect produced was initially hailed by Crookes and others as evidence for the existence of radi-
ation pressure in light, and was used to measure quantities of illumination, hence the name “radio-
meter” or “light-mill.” By the late 1870s, the radiometer effect was understood to be due to residual
gas in the container, which produces tangential forces on the edges of the vanes, as discussed by Max-
well (see Maxwell 1879) and Osborne Reynolds (Reynolds 1879). See Brush 1976, chap. 5.5, for a
historical review of the early theoretical explanations of the effect, and Garber et al. 1995 for docu-
ments relating to Maxwell’s contributions. See Woodruff 1966 for a historical review of Crookes’s
experiments and the response to them, and Woodruff 1968 for a brief account of later radiometer work,
including that of Einstein 1924. For a contemporary review, see Loeb 1927, pp. 295–308.
[5]Wilhelm Westphal (1882–1978) was Titular Professor of Physics at the University of Berlin. He
used a highly simplified model of the gas in the radiometer in an attempt to explain the radiometer
effect at the pressures found in the Crookes radiometer (see Westphal 1919a; see also Doc. 118 for
more on Westphal’s model).
[6]Boltzmann 1896.
[7]The accommodation coefficient measures the efficiency with which molecules of a gas
exchange heat with a wall or other surface. It equals 1 (one) when molecules rebounding from the
wall have the same temperature as the wall itself.
[8]Presumably Janka Meissner (see Einstein to Paul and Maja Winteler-Einstein, 23 September
1918 [Vol. 8, Doc. 621], note 8), a participant in the Zurich Physics Colloquium (see Doc. 131).
K
Nλk∂τ
2
---------------
∂x
N
2
---------------------------21kT–Tλ
l
= =