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162. From Robert A. Millikan[1]

[Pasadena,] November 27, 1923

[See documentary edition for English text.]

163. From Théophile de Donder[1]

5 de l’Aurore Street, 30 November 1923

Sir and very honorable Colleague,

I have taken a lively interest in your new research that seeks to make the a priori

introduction of electrical density disappear and leads all study of the gravitational

field accompanying the pure electromagnetic field back to the ten functions

and the six functions.

I would be very glad to obtain some clarifications on the following point; you

obtain:[2]

and yet, in the old expositions[3] we had:

,

where represents the generalized potential vector. One would thus have

to have:

,

where Ψ is another arbitrary function of . When I transport these relations

into a Maxwell-Hertz field, I find them irreconcilable in a general way with the

classical relations:

gαβ

fμν

–fμν

1

β©

-- -

∂xν

∂iμ

∂xμ¹

∂iν

–

¨ ¸

§ ·

=

fμν

∂xν

∂Φμ

∂xμ

∂Φν

–=

Φ1…Φ4

iμ

β

--- -– Φμ

∂xμ

∂Ψ

+ ≡

x1…x4