By noun, I mean as opposed to phrase; i.e., unless I'm missing something this does not seem to touch particularly on why "man of science" [/ "men of science"] was not thought to be acceptable, given that it was apparently used about twice as frequently as "natural philosopher" in the surviving books of the time.

I also just noticed that in the 1831 letter, Whewell seems to have been sufficiently impressed by Somerville's book as to write her a poem about it. Such things were presumably more common at the time given that this was the Romantic era, but nonetheless would seem to sugesst that it made an impression on him.