Not a "stupid" question at all. I have no clue myself, but you will probably get a more knowledgeable response if you post this over in the Prototype information for the modeler portion of the forums.
Ray Seneca Lake, Ontario, and Western R.R. (S.L.O.&W.) in HO
We'll get there sooner or later!
Not a stupid question at all.
I have several Plastic B&M steamers from places like Bachmann, IHC, P2K and none of them have the arches cab windown.
I have several Brass B&M steamers from places like Pacific Fast Mail, Sunset, Precision Scale Models and Westside Models, all of them have the "correct" arched cab windows.
Sometimes you have to spend a little more for the brass if you want the realism.
Michael
The Bachmann Reading Consolidation (not the Spectrum model, but the older one with the "pancake" motor) has arched window tops. The little Mogul, shown below, is an ex-B&M B-15 and also has arched window tops. I added the sunshades to hide them, though, rather than modify the cab.
I think that the arched window style was more common in the late 19th- and early 20th century, although some eastern roads did stick with it longer.
Wayne
I don't think there are any structural or operational reasons for arched cab windows. As far as I can see they were purely decorative, a styling feature if you like. As Dr Wayne noted, it seems to be a feature associated with older locomotives, and I've noticed that certain loco builders favoured them. I don't believe that ice or snow were a factor in having them, as they are often seen on locos that ran in places that would never see snow - ATSF locos in the US, and many locos in India, South Africa and Australia.
Arched cab window on an Australian loco, NSWGR 3526. L to R, my son Harry, my wife Paula, and my regular fireman Simon. Photo taken by me in April 2008, at Maitland during SteamFest.
Thanks for the help all. I guess since I'm modelling the B&M I've been a bit shortsighted by not noticing other rail lines that had / have the arched windows. I was actually hoping that the arched window was some elaborate scheme to make the B&M different from all the others. Oh well.
Okay so now I'm back to cutting and gluing my styrene!
I think arched windows were generally common on 19th century engines but later changed to square just because it was easier to build it that way. Some railroads chose to keep the arched windows. It's more an ornamentation than a practical matter I believe.