128 PHOTO-TELEGRAPHY 



fitted with a receiving apparatus, and sketches or 

 plans could be transmitted between different 

 sections of an army. 



Mr. Hans Knudsen was the first to demonstrate 

 a wireless apparatus, and I have since effected 

 satisfactory transmissions by two new methods, 

 which would be possible in actual practice over 

 considerable distances, the latter method when 

 developed being, in the opinion of some of our 

 best wireless experts, capable of working across 

 the Atlantic. The scheme of Knudsen would 

 not, in my opinion, be practicable over any dis- 

 tance, for reasons that have been made clear by 

 experiments carried out in my own wireless work. 



Knudsen employed a flat plate on which a sketch 

 in raised lines or a photograph in which the dark 

 parts were resolved into lines in relief was placed. 

 This travelled up under a style and back again, each 

 upward travel being a fraction of an inch to the side 

 of the previous one. A metal stylus was fixed over 

 the flat plate, and this, by grazing against the raised 

 parts of the picture, interrupted the primary of an 

 induction coil, whose secondary was arranged with 

 a spark gap. A coherer was used as the detector, 

 and this was continuously decohered by a striker 

 driven at a high speed by means of a small electro- 

 motor ; the coherer actuated a relay which caused 

 a pointed metal stylus to dig into the surface of 

 a glass plate coated with lampblack an image of 



