DOC.

37

211

Doc. 37

Review

of

M.

PLANCK,

"Lectures

on

the

theory of

thermal

radiation"

("Vorlesungen

über die Theorie der

Warmestrahlung,"

Leipzig:

J.

A.

Barth, 1906.

222

pp.

7.80

mark)

[Beiblätter

zu

den

Annalen

der

Physik

30 (1906):

764-766]

[1]

In the

book

under consideration the fundamental

works of Kirchhoff,

W.

Wien

and

the

author

have been

united into

a

whole of marvelous

clarity

and

[2]

unity,

so

that the

book

is

superbly

suited for familiarizing the reader

fully

with the material-even if the

area

dealt with

has been

totally

unfamiliar

to

him.

In

the first section

(pp.

1-23)

the basic

concepts and terms (such

as

"emission

coefficient,"

"coefficient

of diffusion," "reflecting surface,"

"smooth" and

"rough

surface,"

"black

surface,"

"black

body,"

"coefficient

of

absorption,"

"pencil

of

rays,"

"intensity,"

"radiation

density,"

etc.)

are

first defined and-insofar

as

they

are

definitionally

interrelated-linked

together mathematically. Then

(pp. 23-48)

the

Clausius relation

concerning [3]

the ratio of radiation densities

in

media

with different indices

of

refraction

as

well

as

the Kirchhoff relation

between emissivity and absorptivity

are

derived.

[4]

While

up

to

this

point only

the

laws of

ray

optics

have been

employed,

the

second

section

(pp. 49-99) employs

the

Maxwell

theory,

though

exclusively

for the derivation of the radiation

pressure. The

magnitude

of

the latter,

as

the author

emphasizes, cannot

be

obtained

from

considerations based

on

energe-

tics.

With

the aid of the

expression

obtained for the radiation

pressure,

the

[5]

Stefan-Boltzmann

law

and the

Wien

displacement

law

are

derived, and

the

con-

cepts "temperature

of

monochromatic

radiation"

and

"temperature

of

a

monochro-

matic

elementary

pencil

of rays"

are

defined.

The Wien

displacement

law

yields

for the

energy

density

u

in

the

normal

spectrum

the

equation

u

=

v3q(T/v),

where

T

denotes the

absolute

temperature and

v

the

frequency.

Sections three

and

four

of

the

book

(pp.

100-179)

contain

an

exposition of

the author's

fundamental

investigations

aimed

at

the determination of the function

q

that

appears

in the

Wien

displacement

law.

Even

though

this

goal

could

not be

achieved

in

a

purely