D O C U M E N T 4 3 J U N E 1 9 2 0 1 8 1

(2)

it follows from (1) and (2):

Thus the pressure tensor is calculated.

It is clear, incidentally, that terms of the pressure tensor that contain second de-

rivatives of the temperature, according to location, cannot result out of

this consideration.– *

As I am writing all this down, I suddenly have second thoughts about the whole

theory. The length of path does not enter into the expression, rather, e.g.,

must be expressed by a formula of the form , where can now only

depend on molecular mass m, temperature T, and molecular density n. has the

dimensions , which in the available quantities is only in the form

Nonsense! Heat flow still has to be incorporated, of course! This thing is

correct.[9]

Please put a little pressure on Edith to finish off the matter. Specifically, she

ought to calculate an example to a quantitative and, if possible, an experimentally

verifiable level. I do indeed believe that she was held back and think it very nice of

you to defend

her.[10]

Give her my regards.

With best regards to you and the rest of my Zurich physicist friends, I am, yours,

A. Einstein.

*The paragraph in brackets is struck out.

43. To Klaus Hansen[1]

Berlin, W. 30, 5 Haberland St., 4 June 1920

Dear Sir,

I found your letter of May 15 upon my return from

Holland.[2]

I am now ready

for the trip and only await more detailed information from you. Because I am some-

what overstrained, it would be a great relief for me if I could take my stepdaughter,

who is at the same time my secretary—Ilse Einstein—along with me on the

trip.[3]

So as not to incur any additional expense for you, I request that you please procure

T A B

x

T

x

T

C

grad2T

+ + =

A =

B C + =

C .=

x x

2

T

Txx Tyy –

grad2T

1

energy length

-----------------------------------