Charles Sheeler is a bit of an outlier. He is commonly seen as a proto-photorealist, employing many of the techniques to create photorealistic canvases that the photorealists would later use, but he also created a fair amount of more abstract work that can be lumped in with the Precisionists, a group of American painters working in the 30s and 40s.
This painting, Yankee Clipper, is part of a series on 'power' commissioned by Fortune magazine. With these works you can see hints of abstraction, or an unearthly cleanliness; the subjects of Sheeler's paintings are idealized and lack the flaws and imperfections that all material objects must have.
Maybe I'll delve deeper into another of his paintings another time.
I'm not sure what to make of the lack of window sheen/glare looking out. Certainly it is purposeful and moves the view outward, instead of keeping the viewer looking at just the interior of the bus. I guess the biggest hangup I've got about the window's complete transparency is that I find it impossible to unsee the window's nonexistence. It reminds me of the TV scene transition where the camera zooms in "through" a TV screen into the televised scene. An interesting choice, to say the least.
I could stare at Going's work for ever. The light reflecting and diffusing on and in the ketchup bottle is amazing. Yeah, it's just a still-life of what you'd find on a table in any diner in America, but it's also so much more.