400 BELL SYSTEM TECHNICAL JOURNAL 



development. Much valuable data not otherwise obtainable have 

 been secured regarding functioning of telephone equipment under use 

 conditions. This work has related to relays, switches, clutches, ringers, 

 dials, coin collector mechanisms, contact conditions, etc. It has 

 been applied to the testing of materials in connection with impact 

 testing, stress analysis and bending moment. It has also been applied 

 to reduction of noise in apparatus, particularly in machines of the type 

 widely employed for accounting purposes, coin counting, typewriter 

 mechanisms, and other high speed operating mechanisms where it was 

 desired to analyze and remedy certain noise conditions. It has found 

 particular use in fundamental research associated with the production 

 of speech by the vocal organs. High-speed motion pictures have been 

 made of the vocal cords in action employing taking speeds of 4000 

 frames per second. These pictures are particularly valuable to 

 teachers of speech and music and to the medical profession. Such 

 pictures have, of course, great value to engineers working on problems 

 associated with the transmission of speech over telephone circuits. 



A service in high speed photography is available to engineers of 

 the Laboratories as a visual aid to their study of problems associated 

 with the design, manufacture and performance of telephone apparatus. 

 The high degree of portability which has been achieved in both the 

 camera and lighting equipment lends itself well to extensive application 

 of this service to engineers. Figures A to L show series of individual 

 frames illustrating a variety of problems to which this service has 

 been applied. 



High speed motion pictures of a variety of subjects have been taken 

 in color. Color pictures have been made of vocal cords and of photo- 

 elastic effects revealed in transparent materials under polarized light. 

 Such pictures are valuable in studying stress and impact conditions as 

 affecting design of equipment. Stereoscopic high speed motion pic- 

 tures have been made both in color and in black and white. 



High speed motion picture photography is finding increased applica- 

 tion to a variety of problems associated with the work of the Labora- 

 tories. It is believed that more extended applications of its use will 

 follow. 



TYPICAL HIGH SPEED MOTION PICTURES 



A — High speed photographs of an experimental model of the step-bj-step switch 

 showing the wiper rising to the cut-in position and overthrowing on the first 

 contact of its associated bank. Motion pictures of this type disclosed in great 

 detail movements of the wiper involved in the operation of this switch. These 

 movements are so rapid that but little is learned from a visual examination of 

 the switch while in operation. 4000 pictures per second. 



B — These pictures show normal action of the vertical pawl in the step-by-step 

 switch. Again, high speed motion pictures show much that cannot be gained 



