[dcb]

First sentence:
"Tests made by A. W. Gardiner using a one-cylinder engine having indicated that atmospheric humidity has a very appreciable effect on some phases of engine performance"

This paper does not refute that. In fact the proto rocket scientists seem to think the number of cylinders is the variable here.


There are only 2 lines in figure 4, so they are averaging the effects across various mixtures with a large bias towards richness, where we can observe in figure 2 is a "phase" where humidity does not seem to have a positive effect.

Sorry, but I don't think you can connect the dots to your conclusions with this paper alone. You have to understand the paper that preceded it for one thing, which was geared for an automotive audience.