DOC.

283

DECEMBER

1916 271

-I

have not

thanked

you yet

for

your

latest

paper

on

gravitation

sent

re-

cently.[6]

Now I

have received

3 copies

of

it,

all

told,

one

of which

I

gave

to

Weyl

and

one

to Dällenbach.[7] I

must

say

for

myself

that

I

had

not

come as

far

as

to

perceive

the

gap

in

the

system

that

is

being

filled

by it; by

contrast,

Weyl obviously seems

to

have felt

it, since

the

paper

that

he has

transmitted

to

you[8]

also deals

in

part with

the

relation between

gravitation equations

and

the

conservation

laws.-In this

paper

by Weyl,

it

is demonstrated,

as

he told

me,

that the

“finite circumference

of

a

mass-point” (which

I

define for

myself

such

that

when

the

space

is

represented

in

a

Euclidean

manner-for

masses

at

rest,

this

is

meaningful

also in the

third dimension-the

representations

of

the

measuring

rods

are

variable,

that

is,

they

become

so

small for

the

mass-point

that the

measurement

figure approaches

a

finite

limit)

vanishes

through

electrical

charging

of

the

mass-point (that

is,

through

a

very

low

charge,

E/u,

approx.

1/20000

of

this ratio

for

an electron).

Is

this connected to

the

fact

that the

negative

gravitational

energy

of

the

mass

point’s

field

is counterbalanced

by

the

electrical

field

energy (at

this

low

charge already)?

You

are

going

to

say:

Lazybones, figure

it

out for

yourself!

But

my thinking

machine has become

so

resinous, ought

to

think

out several

things-and

therefore refuses

this

enterprise, quite

as a

matter

of

principle.

But this

does

not

prevent

me

from

telling

others

about what

I

do

not

know

myself.

Thus

I

want to

offer

an

aperçu

in

the

phys. colloquium on

earlier

attempts

to

explain perihelion motion,[9]

likewise

on

the

papers by

Wiechert[10]

and

Flamm.[11]

Regarding

those

explanation

attempts, I

have found

interesting

material

by

Zenneck

on

gravitation

in

the

Enzyclop.

der mathem.

Wiss.[12]

I

have

also

thought

about

Gerber’s

idea:[13]

It

can

be

presented

in

a way

that

makes

it

appear entirely

reasonable:

The

potential

applicable

to

the

moving

point

has

a

value

corresponding

to

its

location at

a

time

sufficient

for

an

effect

to be able

first to reach

the

Sun and

to return

from it

to

the

planet

in

that

interval.[14] Why

Gerber

identified

this

effect

specifically

with

the

potential

and

not

with

the

force,

for

inst.,

or

with

an

arbitrary

function

of

the

potential,

is naturally not

clear.

It

is

not

more

unreasonable,

though,

than

many

other

attempts to

straighten

out

novel issues. On

the other

hand,

it

appears

to

me (see

lazybones

remark

above!)

that

although

the

correct

value should

come

out

for

Gerber,

the

opposite

sign

for

the

perihelion

motion would have to

result-at

least

if,

as

a rough

comparison

of

the

results

suggests

to

me,

with

a

potential of

the

form

k/r

(1

+ adr/at+b

[dr/dt]2),

the result

turns

out

proportional to

the

third

term’s

coefficient.

For

the

Flamm

paper also,

I

have

to

consider

nothing

but

things

I

know

nothing

about.

For

an

unalterable

mass

configuration,

a

practical

elimination

of

space

and

time

occurs

again.

Does

light

describe

the

straightest

lines in

the