Forgotten subway

In an article that explains that American governments are getting too carried away with the unproved technology of hyperloop, I found this bit:

There is reason to think high-speed vacuum-tube transportation can work, at least on paper. (A pneumatic subway briefly opened beneath Manhattan in 1870.) 

 Wikipedia has an entry about that short lived, short length, pneumatic subway, and it also notes that a similar novelty subway was built before that at the Crystal Palace in London.

The things you learn...