I'm looking for a reference that has a discussion of solid angles. Many facts about them are available in various places online, but I haven't had any luck finding a text that treats them. I might be barking up the wrong tree, but neither Do Carmo's Differential Geometry of Curves and Surfaces nor any of the volumes of Spivak's A Comprehensive Introduction to Differential Geometry (save a brief problem in volume I) covers them. Neither does, for example, Marsden and Tromba's Vector Calculus. Perhaps texts on mathematical physics would be worth consulting.
I would be grateful for any pointers!