According to Wikipedia, pneumatic thermostats were invented after electric thermostats.
Yet this article claims that "at least 25 percent of U.S. commercial buildings are served by pneumatic controls, according to the U.S. Department of Energy". I would guess that they were even more popular in the past.
This seems surprising. Why set up an air compressor system and run pneumatic tubes through the walls? Wouldn't an electric system be easier to set up and maintain?
What were the factors that made pneumatic thermostats so popular?