Some gorgeous illustrations from Telephony and Carrier Currents, an International Correspondence Schools textbook published in 1934.
I love this style of drawing. It has a hard practicality, and also a strangely haunting prettiness, right at the intersection of engineering and art.
Shout out @metkis for your patent illustration post earlier, which reminded me to dig out this book.
@th
Spectacular! It must have taken weeks at least to make these engravings.