Alantine & Carf tuning fork C=517.3

[DAEL]

Anyone ever heard of this Company? The fork has on it;
"Pianos Manufacturers' Association N.Y. International Pitch"
"Sheffield England".

I did a search on this company and did not find anything.

From site:
http://www.practicapps.com/csun/411/lecture11.php?src=
This pitch was official in France in 1859:
435.0 A
517.3 C
Paris, France
1859
The French 'Diapason Normal', set in law by the French government acting with the advice of Halvy, Meyerbeer, Auber, Ambroise Thomas and Rossini, although the mean of several forks set to this pitch lies slightly higher at a'=435.4 which is equivalent to c''=517.8