84 DOCS.
69,
70
APRIL
1915
This
observation
suggests
a
modification
of
my
covariance
proof
in which
only
the
61
variations
are
used,
since
the
S2’s
contribute
nothing
to the
decisive
quantities,
ƒ
y/göfTdr.
With
cordial
greetings, yours very truly,
A.
Einstein.
I
have
never
experienced
such
an
interesting correspondence.
You
should
see
how
much
I
always
look forward to
your
letters.
Many
thanks
for
your
article.
70. To Hans Albert Einstein
[Berlin,
before
4 April
1915][1]
My
dearest
Adn,
You
already
wrote
me
two
little letters that
pleased
me very
much.
Did
you
write
them
nicely by yourself
as
well? We
can’t
see
each
other
at
Easter
now.
But
in
the
summer
I’ll
take
a
trip just
with
you
alone for
a
fortnight
or
three
weeks.
This
will
happen
every
year,
and Tete
may
also
come along
when he
is
old
enough
for it.
I
don’t know
yet
where
we’ll
go
hiking,
perhaps
to
Italy.
Then
I’ll
also tell
you many
fine
and
interesting things
about
science and much
else. I
am
very glad
that
you
are
enjoying
geometry.[2]
It
was
my
favorite
pastime
when
I
was
already
a
bit
older
than
you,
around
12 years
old.
But
I
had
no one
to
demonstrate
anything to
me,
I
had
to
learn it from
books.[3]
I
would
immensely
enjoy being
able
to
teach it
to
you,
but that’s
not
possible.
If
you
write
me
each
time
what
you already
know,
I’ll
give
you
a
nice
little
problem
to solve. I
gave
mathematics
lessons
to
the little
Haber
boy
because he
was
sick
for
a
long
time.[4]
He
is
a
smart
boy,
but
ailing.
Today
I’m
sending
off
a package
with
some
toys
for
you
and Tete.
It
is
as an
Easter
greeting.
Don’t
neglect
your piano, my Adn; you
wouldn’t believe how
much
pleasure
you
can give
to others
as
well
as
to
yourself
when
you
are
able to
play
music
nicely![5]
What
are
your
friends
like?
Another
thing,
dear Adn. Brush
your
teeth
every
day,
and
if
a
tooth
is not
quite
all
right
go
to
the dentist
immediately.
I
also do
the
same
and
am
very
happy
now
to have
kept enough healthy
teeth.
This
is
very important,
later
you
will realize it
yourself.