sd90ns, Yes, that is an air horn seen above left compressor. I do not know, for sure, but I have always thought they were piston pumps. They sounded like those on the cabforwards and wheezed with each stroke. Not sure if they were steam powered, in all the pictures I have which includes all 12 engines, there is no evidence of steam exhaust or leaks on the front of loco.
Steam. The photos in your posts #7 and #14 clearly show the pipes into and out from those duplex pumps.
If you think about it, the steam locomotive was the first piece of real "Technology" most people ever came into contact with. Prior to the steam engine/locomotive pretty much everything that people used or encountered was a version of something that had been around forever in one form or another. George Washington could travel overland no faster than an Egyptian Pharos from 3,000 BC, then suddenly . . .
But think of the technologies that had to be developed prior to being able to generate the idea of harnessing steam to provide power for a method of travel.
Metallurgy is the first thing that comes to mind a "science and technology" literally millennium in the making and spread across half the world. The steam engine and the locomotive pretty much came instantly and out of nowhere when compared to the above. It has been pointed out more than once that there has been more technological development and scientific discovery in the last 150 years than in the previous history and pre-history of mankind. The first steam locomotives showed up in the 1820's and we were on the moon less that 150 years later. This has also boon pointed out to be at the heart of many of humanities problems. We had 100,000 years as a "Hunter gatherer" and a few decades of "Being able to blow ourselves up". We simply haven't had nearly enough time to evolve into it.
Our societal conventions have yet to catch up to the frontiers that our grasp of technology has moved society into.
Of course, somebody had to discover wood and coal burns and that water turns into a gas when it gets hot enough. Doug
It's not simply "societal conventions" that haven't kept up, our brains and basic thinking patterns haven't evolved enough to handle modern society brought about by technological advancement. It is the equivalent of running bleeding edge software on a TRS-80.
That would be safer - TRS-80 would not have the storage space for the software let alone the computational power to make the software do anything.