So, I used Google ngrams several times in the past few weeks to see which terminology for the London Underground appear most often in print.  Very interestingly, these were my results.  I was a little surprised at first when “Metropolitan Railway” had the most hits historically.  Of course, it tapers off after 1935, which is around the time that a lot of the underground building and expansion was happening.  With the decline of the term “Metropolitan Railway,”  “London Underground” began to rise sharply.  This was not particularly surprising.  It was surprising, however, that the term “London Tube” doesn’t appear very often in comparison to other terms.  Especially because it has become a very commonly used term for the system — and its usage actually declines towards the year 2000.

The issues that I’ve discovered with Google ngrams is the capitalization issue.  While it’s great, because it helps separate proper nouns from common nouns, it creates an issue for terms such as “London tube” vs. “London Tube.”  They mean exactly the same thing, but Google separates them.

Also note, that Google only studies a limited number of texts… and who knows what bias led them to add certain texts over other types of texts.