56 DOCUMENT 48 JULY 1907
48.
To
Conrad
and Paul Habicht
[Bern,
15
July
1907]
Meine lieben Habichte!
Ich möchte Euch
gern
wieder einmal sehen! Könnt und wollt Ihr nicht bald
kommen? Jetzt im Laufe des Juli könnte ich Euch beide
zusammen
beherber-
gen,
weil meine Schwester verreist ist. Noch hübscher
wäre
es,
wenn
Ihr An-
fangs August
nach Lenk im
Simmenthal[1]
kommen
würdet,
wo
ich
am
1.
Au-
gust
mit
Weib
und Kind
hingehe,[2] um
ca
10
Tage
Ferien dort
zu
verbringen;
da hätte ich eben den
ganzen
Tag
frei. Herrn Paul danke ich bestens für den
interressanten Brief. Ich habe noch eine
neue
Methode
zur
Messung
sehr klei-
ner
Energiemengen gefunden.
Beste Grüsse
von
Haus
zu
Haus Euer
A. E.
Schreibt bald!
AKS (Walter Habicht, Rodersdorf, Switzerland).
[70
300].
The
verso
is
addressed "An die
Herrn Konrad und
Paul
Habicht Fulacherstr.
Schaffhausen.,"
and
postmarked
"Bern
Brf.Exp.
15.VII.07.-1."
[1]A village (1070
m)
in
the Bernese Oberland.
[2]In
a
postcard
written
on
the
eve
of their
trip
Einstein-Marid informed the Habichts that
the Einsteins would
go
on
foot from Zweisimmen
(964
m)
to
Lenk
(a
distance of
13
km),
where
they
would
stay
at
the Hotel Hirsch
(see
Mileva Einstein-Marid
to
Conrad and Paul
Habicht,
31
July 1907,
Walter
Habicht,
Rodersdorf).
EINSTEIN
ON
SUPERLUMINAL SIGNAL VELOCITIES
I
In
six
letters
to
Wilhelm Wien
dating
from
summer
1907 (Docs.
49-53
and
55),[1]
Einstein discusses the
occurrence
of velocities
exceeding
the
speed
of
light in
disper-
sive and
absorptive
media and tries
to
answer
the
question
whether such velocities
are
the
physically meaningful signal
velocities
relativity theory requires
to
be less
than
or
equal
to
the
velocity
of
light. Though failing
to
convince
Wien,
Einstein's
let-
ters
refine and
expand upon
his
published
treatments
of
the
possibility
of
superlumi-
nal
speeds.
Discussion of the existence of
superluminal
velocities within the framework of
Maxwell's
theory goes
back
at
least
as
far
as
1889,
when Oliver Heaviside considered
electric
charges traveling
at
superluminal
speeds.[2]
As
the various
competing
elec-
tron
theories
were
developed
in the first
years
of the twentieth
century,
the
question
of
superluminal speeds
was
taken
up
from the
point
of
view
of electron
theory,
in
par-
ticular
in
connection with the
structure
of
the
electron.[3]
Through
the work of Arnold
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