The Whig theory of the history of science is very similar, of course, to the Whig theory of the history itself. The Whig theory of history of science was dominant until the 1960s. (It probably still is dominant in high school textbooks.) It essentially said that science, the growth of knowledge, is an onward-and-upward, step-by-step approach, from the year zero to now.
What are the implications of that? One implication is that you don’t have to read a history of science unless you’re an antiquarian. If you’re a physicist in 1986, there’s no point in reading some physicist from 1930; unless you’re interested in the special conditions of what happened to him, you don’t learn anything from it.
In other words, you never lose any knowledge. The theory is that, every step of the way, science patiently tests its assumptions and premises; it discards those that turn out to be unacceptable, false, and adds those that are acceptable. Everybody’s always patiently testing their axioms, steadily advancing. Therefore, there’s no loss of knowledge.