Transcriber’s note: Four likely printer errors have been corrected; these are on pages 46, 115, 176 and 186, marked like this. The inconsistent hyphenation of “break-down”, “electro-motive” and “vibration-head” is as in the original. Some of the illustrations had to be moved up or down a few paragraphs from their position in the original; the hyperlinked page numbers in the List of Illustrations point to the original locations, but the hyperlinked figure numbers point to where the figures are now.