Two frequently asked questions are 1) how famous was Wallace, and 2) was he really forgotten after his death as some people (like myself) have often said? Responses to these have been based on intuition - but now, thanks to Google's Ngram Viewer, it is possible to answer them in a more quantitative way. Ngram allows users to study the frequency of certain terms (e.g. people's names) in about 5 million books over time. Several terms can be examined on one graph, so one can examine their relative frequencies. Below I show four Ngram plots which give a pretty good idea of how famous Wallace was over time relative to, firstly 5 biologists who were his friends or colleagues, and second, to a selection of other very well known biologists, living and dead. I realise that the frequency that someone's name is cited in books over time is not a direct measure of their fame, but I would argue that it is probably a pretty good surrogate. In any case, for the sake of argument I will use the term "famous" to mean "mentioned in more books than someone else".
The graph below shows a few interesting things. Firstly that the geologist Charles Lyell appears to have been far more famous than Charles Darwin until around the time of Darwin's death in 1882. Darwin then became and remained by far the most famous of the people shown. I think that the former pattern is probably an artifact, however, since if you plot an Ngram using just the two men's surnames, it shows that Darwin was in fact more famous than Lyell after about 1850. The problem with using just surnames is that there may be several people with the same name. Another interesting pattern is that citations of Darwin's name seem to really start accelerating in the late 1980's - not long after the Darwin Correspondence Project started to publish his collected correspondence. This is what I have always believed based on intuition, so it's nice to see that the graph seems to show this.
Removing Darwin from the graph and looking at just the period from 1990 to 2008, we see that by 2008 Wallace and botanist Joseph Hooker are on a par and that they are more cited than Huxley and Owen, but that Charles Lyell is a bit more famous than either.
Comparing Wallace with some other famous biologists, living and dead, we see that he was about as famous towards the end of his life (he died in 1913) as Stephen Jay Gould and Richard Dawkins were as of 2008, and that he is now about as famous as Edward Wilson.
These graphs show some things I expected (e.g. that Darwin was always a lot more famous than Wallace and that Wallace's fame decreased soon after his death and is only now increasing again), as well as some I didn't (e.g. how famous Wallace was in his lifetime relative to what I thought were even more famous people like David Attenborough). It is interesting that citations of Wallace's name start to increase in the 1970's, and I think that the reason is that it was then that scholars (such as Lewis McKinney, Barbara Beddall and Wilma George) started to become interested in him.
I'm sure one could argue that there are problems with this method as a way of measuring fame, but it is the best technique I can think of.