Re: "Clairaut's formula": Equation, theorem or other?

Anonymous wrote: 
The other day I came upon a web page that briefly mentioned "Clairaut's formula" ( http://williams.best.vwh.net/avform.htm#Clairaut ).
I googled the term and came up with "Clairaut's Equation" and "Clairaut's Theorem", neither of which seem related to the "formula".
What is the formal definition of Clairaut's *formula* and are there any other web pages (other than AF, which all other "formula" references seem to refer to) that deal with it?

Thanks



  See third equation at:
    http://scienceworld.wolfram.com/astronomy/PlanetographicLatitude.html


  Also
    http://www.britannica.com/eb/article-9330
.