2 3 6 D O C U M E N T 1 0 5 A U G U S T 1 9 2 0
105. From Théophile de Donder
Brussels, 11 Forestière St., 18 August 1920
Sir and highly esteemed Colleague,
All my thanks for your kind
mailing.[1]
At present, I am in Nismes (province of
Namur); consequently, it was impossible for me to come into possession of the
notice[2]
that you were kind enough to advise me to consult. I am impatient to be-
come acquainted with it upon my return to Brussels.
I am very sorry that my notation causes confusion. In my way of writing, the op-
eration
[contains] the complete
derivatives;[3]
hence, the presence [of the] numerical factor
(1 + ). Thus, to fix the ideas, let us calculate:
If, on the contrary, we prove the partial derivatives, one will obtain:
On the other hand:
is identical to:
This numerical binomial is also present in the notices by Mr. Hilbert; he, how-
ever, informs the reader that everything [is]
understood.[4]
All my calculations [in which] the Lagrangians appear next to have fur-
nished results in perfect harmony with
yours.[5]
I hasten to add that I had already decided to adopt your very clear way of indi-
cating the covariants, contravariants, symmetries, asymmetries, etc., in my future
notices.
12 g11
2
g12g21
–
dg12
d
g11
2
g12g21
–
.–21g2
E
12
g11 2 g12g21 – g12
g11 2 g12g21 –
–g21
11 g11
2
g12g21
–
d
dg11
----------
g11
2
g12g21
–
2g11
E
11
———
g11
———
2g
11
.