62 



PHOTO-TELEGRAPHY 



being drawn with a pen and some ink that was 

 essentially an electric insulator upon a metal base. 

 Thus the first materials sent to me by Professor 

 Korn were some sheets of copper foil, a quill pen 

 and some ink composed of an alcoholic solution of 

 shellac strongly tinted with a violet aniline dye. 

 Now, if we draw a sketch on copper with this ink, 

 and connect the under side of it, i.e., the plain 



FIG. 28. 



copper side, with one pole of an electric battery B 

 (see Fig. 28), the other pole of which is connected 

 to one terminal of a galvanometer G, and we 

 connect the other galvanometer terminal with a 

 pen P, this consisting of, say, a darning needle, 

 and we now draw the " pen " slowly over the surface 

 of the sketch, we shall see that whenever the pen 

 crosses a line of the drawing, i.e., a shellac line, 

 the galvanometer needle is at zero, while when the 

 pen is in contact with the bare metal correspond- 

 ing to the paper of an ordinary sketch the galva- 

 nometer needle is deflected. 



