Elementary telegraphy : a manual for students; written specially to meet the requirements of the ordinary grade of the subject as published in the syllabus of the city and guilds of London Institute (1910)
Pendry, H. W. (Henry Walter) · London ; New York : Whittaker & Co. · leaf 55
Fi(i. I.i.—Hart positive gn<l. Fifi. 10((.—Hart positive plate(grid pasted and rolled). The negative plate is of the interlaced grid designand is the most modern form. The pellets are horizontal
Telegraph
Internet Archive · Gerstein Library, University of Toronto · Public Domain Mark 1.0. Free to use for anything.
