DOCS.

59,

60

MARCH

1915

71

could be

taken

instead;

because

if

the

mass

is

critical

at

the

developmental

stage,

then

for

binary

stars

the

mass

of

the

components

is

much

more

critical

than the

overall

mass.

5)

You should

provide

me

with

a

bit

more

precise

information

on

how

the

radii

of

the

eclipses

are

estimated.[6]

6)

Is

the

absence

of

the

effect

really

proven

for

types

that

yield

smaller

masses

using

the

binary-star

method?

Why

do

you pass

over

this

important

question

so

quickly?[7]

7)

Did

you keep yourself open

to

the

hypothesis

that

for

stars

with

only one

visible

component,

both

components

have

masses

in

the

same

order of

magnitude?

It

is

a

shame that

your descriptions

are

not

detailed

enough

to

be

able to

es-

timate the

uncertainty

attached

to

your

estimates.

Thus

a

nonspecialist

cannot

get

a

notion

of

the

reliability of

your

calculations. A

much

more

in-depth

pre-

sentation

would

be

desirable.

The worst in

this

regard

is

the

specification

of

the

mean

densities.

In

the

formula in

the fourth

column

of

the

proofs, “V0.1”

is inadvertently

indicated[8]

instead

of

“3V0.1.”

With best

regards, yours,

Einstein.

60. To

Tullio Levi-Civita

[Berlin,]

5

March

1915

Highly

esteemed

Colleague,[1]

By examining my paper

so

carefully, you

are

doing

me a

great favor.[2]

You

can

imagine

how

rarely

someone

delves

independently

and

critically

into this

subject.

I also cannot

help admiring

the

uncommon sureness

with which

you

make

use

of

a

language

that

is

foreign

to

you.

When

I

saw

that

you

are directing

your

attack

against

the

theory’s

most

important

proof,

which

I

had

won

by

the

sweat of

my

brow,

I

was

not

a

little

alarmed, especially

since

I

know

that

you

have

a

much better command

of

these

mathematical

matters

than

I. Nevertheless,

upon thorough

consideration

I

do

believe I

can

uphold my

proof.[3]

I

start

with the

second

part

of

your

letter

in which

you

intend

to

show with

an

example

that the

result

of

§14,

that

Euv/-g

is

a

tensor,

is not correct.

For

this