Caution: I'm new at this stuff. On page 573 of Gravitation (Misner, Thorne, Wheeler), they write down what I think is the electromagnetic wave equation for a discussion on Optics, "Next insert the vector potential (22.25) into the source-free wave equation (22.19d):" I am wondering if the equations mentioned, 22.19d, and 22.25, are applicable to any dimension, for example 4+1 dimensions as in Kaluza-Klein theory, and higher dimensions? I ask this because I was wondering how to write the good ole equation for a propagating electromagnetic wave in higher dimensions, such as 4+1 or higher. I have read that the curl cannot be written in some higher dimensions in the customary way at least, without going to differential geometry and topology. And so I was wondering if these 2 equations, written with tensors, hold for higher dimensions? Thanks.