Where did the idea of "rocket tubes" come from?

I can't remember where I first came across it, but I know that I read at least one old SF story as a child which referred to "rocket tubes". I'm not asking for story identification. I know there were many stories that used the concept. I can tell this even without reading many such stories, because 1930s-50s SF pulp cover art (among other things) frequently depicts spaceships with clusters of tubular engines. Example of them being explicitly "tubes".

This doesn't match the real appearance of rocket nozzles. Where did this concept come from?