388

DOC. 24

DISCUSSION OF GDNA LECTURES

Doc.

24

Excerpts

of

Discussions

Following

Lectures

Delivered

at 83rd

Meeting

of

the Gesellschaft Deutscher Naturforscher und

Arzte,

25

and

27

September

1911

[Physikalische

Zeitschrift

12

(1911): 978, 1068-1069,

and

1084]

Stark:

The

speaker

said

that

an

electron

resonates

without

damping

in

response

to

incident monochromatic radiation until the time

a

quantum

of

action, or,

to

use

the

Planck-Einstein

expression,

an

energy quantum

has

accumulated

in it. I would like to ask

whether

a

calculation has

been

performed regarding

the

length

of time the

resonance

needs for the

accumulation

of

a

light

quantum.

This

question comes

to mind because it

was precisely

Lorentz

who

performed

detailed

calculations

on

this

point

and

who

pointed

out

that, even

in

the

case

of

perfect undamped resonance,

the

lengths

of

time

one

would

have to

assume

in

order

to

explain

the

maximum

kinetic

energy

in

the

photoelectric

effect

are so

great

that

they

cannot

be reconciled

to within

an

order of

magnitude

with

the

actually

observed situation

regarding

the

intensity

and maximum

kinetic

energy

of the

emitted

ions.

Sommerfeld:

Of

course,

the

magnitudes

that Lorentz found

for

the

time

length

t

are

here

valid

for

monochromatic

light

within

the

same

order of

magnitude.

It

can

be

shown

that

our

results

are

not

confined

to

monochromatic

light,

and this must

be

shown

because monochromatic

light

does not exist.

If

one uses

natural

light as

the incident

light,

and the

laws

found for monochromatic

light

remain

valid

up

to

the

dispersion

mentioned,

then the

difficulty

regarding

the

time

length is

eliminated.

Stark:

But the

light

that

was

used

in

spectral

resolution

was

practically

monochromat-

ic. Ladenburg

worked

with

the

lines

of the

mercury

arc.

Their

frequency range is

very

narrow.

Have

you

performed

the

calculation

for

a

specific

frequency range?

For

example,

for

a

spectral

line with

a

width

of

1

ängstrom.

Sommerfeld: Yes,

for

one

spectral

line.

Stark:

The

consistency

of

such

a

result

with

Lorentz's

calculation would

be

amazing

indeed.

I

assume

that

a

detailed

report

of the

calculation

is

to follow?

Einstein:

Would the time

required

for

a

complete

act

of

absorption

according

to

the

[1]

theory presented

not be

long

enough

to

be

accessible to

observation? In

this

case,

the

experimental

investigation

would

be of

enormous

interest.

Sommerfeld:

I believe

that

it would be

possible

to

compare

the theoretical

[2]

accumulation time

with

experiment.

Stark:

Can the

resonance theory presented

be

extended

to the emission

of cathode

rays

to

the

Roentgen-induced rays?

This would

be desirable because the

phenomenon

in

question

is

completely

analogous

to

the

photoelectric

effect.