'I wasn't surprised by the idea that people used to laboriously do something that computers now do automatically...The surprising thing about these drawings is that they were gratuitous -- they just did not need to be that nice. The illustrator could have simply drawn what was necessary — a partial sphere with a bit of shading, or whatever.'
'..the illustrators put a dazzling amount of attention into the shading and the different line-thicknesses and a dozen other details that are not only gratuitous, but which you are generally expected to not even perceive!'
Sean M Burke has a different sort of online gallery - he has scanned his favourite images from a dozen or so engineering / industrial / mechanical / pneumatic design texts from the first half of the 20th century. [Thanks again D]