DOCS. 606-608
AUGUST-SEPTEMBER
1918 633
I
am
returning
in
the
same
post
both
pat[ent]
publications
as
well
as
the
book
with
the
Van den
Bos
sketch
neatly
modified.[3]
607. To
Michele
Besso
[Berlin,
28 August
1918]
Dear
Michele,
On
rereading your
last
letter, I
discovered
something
that
downright annoys
me:
speculation
allegedly
had
revealed itself
to
be
superior
to
empiricism.
In
this
regard
you
are
thinking
of
the
development
of
the
theory of
relativity.
But
I find
that this
development
teaches
something
different
that
is almost
the
opposite,
namely,
that
in order
to
be
reliable,
a
theory
must be
built
upon
generalizable
facts.
Old
examples:
Main theorems of
thermodynamics
on
the
impossibility
of the
perpetuum
mo-
bile.
Mechanics
on
the
empirically
explored
law
of
inertia. Kin.
gas
theory
on
the
equivalency
of
heat
and mech.
energy (also historically).
Special
relativity
on
the
constancy
of
the
velocity
of
light &
Maxwell’s
equa-
tions for
the
vacuum,
which
on
their
part
are
based
on
empirical
foundations.
Relativity
with
regard
to
unif.
translation
is
an
observed
fact.
General
relativity:
Equivalency of
inertial
and
gravitational mass.
No
genuinely
useful and
profound
theory
has
ever really
been
found
purely specu-
latively.
The
closest
case
would be
Maxwell’s
hypothesis
for
displacement
current.
But
there it
involved
accounting
for the fact
of
the
propagation
of
light
(&
open
circuits).
With
affectionate
greetings, yours,
Albert.
608. To
Paul Ehrenfest
[Berlin,
4 September
1918]
Dear
Ehrenfest,
I congratulate
you
heartily
on
little
Wassily.[1]
Your
will
for
life fills
me
with
admiration.
I
also
am
full of
hope
for
the
future
again,
even
if
I
don’t
give
it
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