Edison His Life And Inventions - Frank Lewis Dyer - Google Books

http://books.google.de/books?id=mD4-fWOs1MkC&pg=PA365&lpg=PA365&dq=edison+menlo+park+electric+gauge&source=bl&ots=E6ZTGJVudE&sig

American youths to-day are given, if of a mechanical turn of mind, to amateur telegraphy or telephony, but seldom, if ever, have to make any part of the system constructed. In Edison's boyish days it was quite different, and telegraphic supplies were hard…