Tracking the rise of the self-filling fountain pen

Google's Ngram Viewer is a powerful tool for evaluating the popularity of words and phrases over time. Here are the results for "self-filler", which neatly illustrate the triumph of the self-filling fountain pen over the dropper-filler in the English-speaking world in the first decades of the 20th century:

The transition peaks between 1915 and 1920, then rapidly falls off as self-filling pens become the new norm.

The dropoff is more pronounced in the second chart immediately above, which is limited to American English sources. This is not a surprise, inasmuch as British penmakers continued to emphasize self-filling in both model names and advertising later than their American counterparts.