116
DOCS. 155-157
MAY 1909
155.
To
Fritz
Reiche
[Bern,
12
May
1909][1]
Highly
esteemed
Dr. Reiche:
Thank
you
so
much for
the
article.[2]
The
investigation
on
diffraction,
with
special
regard
to
the
phase
of the
resulting oscillation, is
very
interesting.
I
only
disagree
with
your equation
f
=
ąg.[3]
The
uncertainty
in the
sign
is
due to the fact
that
you
worked
with
a
second-order
equation
that
you
took
from
the
energy principle,
whereas
the
customary
method
(Huygens'
principle)
would have
yielded
the
sign.
The
passage
to
the
limit from
an
approximate
to
an
exact
crossing-point
of
the
rays
cannot
affect the
phase.
With
collegial
greetings,
yours
sincerely,
A.
Einstein
156.
From Wilhelm
Fiedler[1]
Zurich, 13
May
1909
Esteemed Dr. Einstein:
I congratulate
you
on
your appointment
as
the
representative
of theoretical
physics
at
the
University
of
Zurich.[2]
Judging
from
several of
your
articles,
which
you
so
kindly
provided
for
me,
your
new
activity
will
perfectly
serve
the
goals
that
were
always
on
your
mind while
you
worked
at
the
Patent
Office.
May your
work be crowned with success!
With
respectful
greetings,
I remain
your
old
Dr. Wilh. Fiedler, Prof.
ret.
157. To Alfred
Stern
[Bern,]
14
May
1909
Highly
esteemed
Professor:[1]
Thank
you
for
your
kind
note. I
knew
that
Miss
Dora[2] is
in
Berlin,
for
I
was
together
with
Luigi[3]
this
summer,
and he
told
me
about
you
and
your
valued
family.[4]
It will be
a
pleasure
to visit
you
with
my
wife.
I
still
remember
most
vividly
the
delightful
hours that
I
spent
in
your
hospitable
home.[5] I
now play
the
violin
even worse
than before.
Faithfully yours,
A.
Einstein