Question: I need population figures for various countries starting at about 1850. Is there a resource I can check for such data?

Answer: You should start with B. R. Mitchell's International Historical Statistics: 1750-2005. It's shelved in the Information Center Statistics area and there are three volumes: 1) Africa, Asia and Oceania; 2) The Americas; 3) Europe.

You might also want take a look at databases like JSTOR and Project Muse to see what secondary literature is available on historical statistics.