I've seen several citations of a letter from Weierstrass, talking about his dispute with Kronecker, in which he refers to Christoffel as a 'whimsical eccentric' (presumably the German  original is even more flavorful). In what respect was he whimsical or eccentric?

One reference is Barrow, 'Pi in the Sky,' page 200, quoting the letter from Weierstrass. Was Christoffel generally nutty, or was Weierstrass just citing his support for Kronecker?

The Google translation of the German helpfully supplied by Suvrit is:

> When a strange fellow as Christoffel says that in 20-30 years the
> current function theory is carried to the grave and the whole analysis
> to be worked out in the theory of forms, so you answered that with a
> shrug.

Subquestion: what does he mean here by 'die Theorie der Formen' here?