It's the photos that are 'early', rather than the subject, but I thought this might interest you anyway *s*.

Charles Piazzi Smyth (1819 - 1900), the Astronomer Royal for Scotland, was something of an eccentric and obsessed by the pyramids of Egypt. He was notable for advancing the theory (in his book Our Inheritance in the Great Pyramid) that the Great Pyramid of Giza was a record of ancient knowledge which could be revealed by detailed measurements of the structure. He is the only person to have resigned his fellowship of the Royal Society, after they refused to publish his papers on this subject.

In 1865 he traveled to Egypt to produce accurate measurements of the Great Pyramid, and took a series of photographs inside the the burial chamber of the Pyramid using the light given off by burning magnesium which are one of the earliest known examples of photography by artificial light. You can see a selection from Smyth's Great Pyramid Album on the website of the National Museum of Photography, Film and TV:

Charles Piazzi Smyth: Exploring the Great Pyramid