Certainly a glossary doesn't detract from a science text, but since it takes resources to put together and to print, I'm not sure if it always adds enough value to be worth the effort and cost. Often, the indices of such books have listings for terms and

**emphasize** the page on which the term is introduced and defined, which can take the place of a glossary. It's not quite as self-contained as a glossary, but it gets the job done--assuming both the text and index are well written.

If we had limitless resources, I'd say always add a glossary that not only introduces the terms, but shows briefly how they're used in the main text, including a brief mathematical example if relevant.

For your website, I can say that terms I always struggled with then being introduced to general relativity were covariant, contravariant and pseudotensor.

Also, I didn't read through everything, but

Metric Tensor - A multilinear map from vectors to the set of real numbers that is used for calculating the *magnitude of a vector of the inner product of two vectors* is called the metric tensor and represented as g. The metric tensor is defined such that it is symmetric.

Should the italicized part read "the magnitude of the inner product of two vectors"?