194 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



intensity to corresponding changes of electrical intensity as the scan- 

 ning beam passes over the copy being transmitted. At the receiving 

 end, the intelligence may be reconverted to changes of light intensity 

 and recorded on a photographic film as a negative. After developing, 

 a print from the film negative will give a positive of the original 

 material from which transmission was made. 



The received changes of electrical intensity may be inverted from a 

 negative image to a positive image and recorded by a stylus on dry 

 Teledeltos paper. This gives an immediate positive of the original 

 photograph, message, drawing or other transmitted material without 

 any further processing. Good photograph halftones may be made 

 from this copy. Development of this equipment was halted by the 

 war but our laboratories have resumed research in this method of 

 communication. 



Telefax installations in China have greatly speeded up communi- 

 cations in that country. Prior to Telefax, it was necessary to assign 

 a number to each Chinese character in order to transmit a message 

 by regular telegraph. This required that a message be coded in num- 

 bers, transmitted by standard telegraph, deciphered, and written on 

 a blank. Transmission by Telefax gives an immediate reproduction 

 of the original message with no chances for errors. The entire con- 

 tents of a standard telegraph blank may be transmitted in a little 

 over 2 minutes. 



Outside of the commercial telegraph field, one use for this system 

 has been in the handling of railroad train orders where accuracy in 

 transmission is absolutely essential. 



The transmission of intelligence from the various types of terminal 

 equipment over open wire land lines has proved to be one of our great- 

 est difficulties in the maintenance of uninterrupted service. The phys- 

 ical hazards of sleet, ice, fires, floods, railroad and vehicular wrecks, 

 and tornadoes have caused our Dispatching Bureau many hours of 

 "blood, sweat, and tears." Poor and corroded wire splices, kite tails 

 that get tangled in the line, the boy (and, I might add, the man) with a 

 22 rifle, who finds insulators a tempting target, all add up to the inces- 

 sant patrols by our linemen. 



Interference caused by inductive coupling to power lines, lighting, 

 and the interference induced by adjacent telegraph circuits have lim- 

 ited the distance over which transmission may be satisfactory without 

 repeaters. Wlien the signals become too badly mutilated, they may 

 be rebuilt by regenerative repeaters, but this equipment is expensive 

 and requires expert maintenance and adjustment. 



In a grounded telegraph system such as we use extensively, a bat- 

 tery is applied to one end of the wire and the opposite end grounded, 

 thus completing the circuit through the ground back to the battery. 



