DOCS.

299,

300

FEBRUARY

1917 287

better).

In

the

spring

or

In

the

summer

I

shall

definitely

come

to

see

you

in

Switzerland; traveling

is too repugnant

now,

especially

for

a

rickety

old

fellow.[7]

300. To

Erwin Freundlich

[Berlin,]

Sunday.

[18

February

1917

or later][1]

Dear

Freundlich,

I

have been

turning

the

elliptic space problem

over

in

my

mind and

understand

it

completely. My

calculation remains

correct,

in

particular,

the

relation between

A,

p,

and

R; only,

the total

volume is half

as

large

as

for the

originally spherical

space.[2]

The

elliptic space

is

simply

a

spherical one

in which

points

that

are

symmetric

with

respect

to

the

center

are

identical

(not distinguishable).

Put

another

way,

G

P

P'

Let G

and

G'

be

two

geodetic

lines

that

start

at

P.

These

same

lines intersect

each

other

at

P'.

According

to

spherical geometry,

P

and

P'

are

opposing points;

according

to

the

elliptic one, they

are

identical. An

elliptic space

can

aptly

be

described

as

“hemispherical.”

The star

statistics

question

has become

a

burning

issue to be addressed

now.[3]

I

suggest

that

we

discuss

the

problem

in

a

joint

paper.

If it

is

necessary

or

beneficial,

I shall seek to

have

you

granted

time

off

from

your

duties

for

a

specified

period.

We

must act

cautiously

in

doing this, though,

so

that

your

position

is

not

jeopardized.[4]

The

matter of great

interest here

is

that

not

only

R

but

also

p

must be indi-

vidually

determinable

astronomically,

the

latter

quantity at

least to

a

very rough

approximation,

and

that

then

my

relation between them

ought

to hold.

Maybe

the

chasm between

the

104

and

107 light years

can

be

bridged

after

all![5]

That

would

mean

the

beginning

of

an

epoch

in

astronomy.

The

paper by

Harzer

is

very

interesting.

If

only

it

were

known what should be done with

the

loathsome ab-

sorption;

it

is

so

abominably up

in

the

air.[6]

But

managing

without this

quantity

is

unfortunately

impossible.

Best

regards,

yours,

A. Einstein.