# In interferometry, what is the origin of the name “Airy function”?

In interferometry (specifically, in the domain of Fabry-Perot cavities), the function $$f(\phi) = \frac{1}{1 + F \sin^2 \phi}$$ , which describes the shape of the resonant structure of the cavity, is often called the "Airy function" (for instance, in Wolfram Mathworld). However, it is obviously quite different from the special functions Ai(x) that usually go by that name.

This function resembles probability density function of the wrapped Cauchy distribution.

How did it get the name "Airy function"?

I've heard that Fabry and Perot gave it this name in one of their original papers (maybe this one? PDF, in French, which I can't read), in honor of (the same) George Biddell Airy who had earlier considered similar interferometers. It would be great if someone could help ferret out the first reference to that function by this name.

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 In the paper in French he uses the term "Airy formulas" like a well known name for these formulas... maybe defined in one of his earlier paper ? – Cedric H. Nov 9 '10 at 20:40 According to this page: skullsinthestars.com/2008/10/16/…, the first paper is called "C. Fabry and A. Perot, “Sur les franges des lames minces argentées et leur application a la mesure de petites épaisseurs d’air,” Ann. Chim. Phys. 12 (1897), 459.". – Robert Smith Nov 9 '10 at 20:54