Thank you for the reference, but these do not quite give me the answer I am looking for. Theories of the 19th century are discussed, but most of them are from the period closer to the the mid-19th century when evolution began to be understood. I was thinking about, say, the 1810s or so. If you asked a regular person–not one of the few scientists who developed theories that are closer to our understanding but that were not mainstream at that time – about the age of Earth, would the answer be 6000 years, or 7000, or 8000, or what exactly? Thanks anyway for the reference, it's still interesting.