HIGH SPEED MOTION PICTURE PHOTOGRAPHY 401 



from visual examination. In this case, the pictures revealed whether or not the 

 action of the pawl and ratchet was satisfactory under extreme operating condi- 

 tions. 2000 pictures per second. 



C — To study the conditions under which handset breakage might occur, apparatus 

 was developed in which breakage takes place under controlled conditions. High 

 speed photographs revealed distortions in the handset which under certain test 

 conditions resulted in breakage at the moment of impact. Information relating 

 to the structural strength of the handset was secured from measurements made 

 on many individual pictures of this series. The pictures shown illustrate break- 

 age of an experimental 3-piece E type handset after falling from a height of 

 5 feet and striking a rigid steel bar shown at the bottom of each picture. 4000 

 pictures per second. 



D — Information gained from a study of high speed pictures of the type represented 

 by C resulted in strengthening of the reenforcement of the handle at certain 

 points which reduced the possibilit\' of breakage under normal use conditions. 

 4000 pictures per second. 



E — High speed photography is applied extensively to the study of explosion of gases 

 in motors, to ballistic problems associated with the explosion of gun powder 

 and to other rapid phenomena of a self luminous type. This series of pictures 

 shows the melting and burning of fuse wire under heavy current conditions. 

 20-ampere fuse wire is shown during burn-out on direct short. The violence and 

 extent of the action are well shown in these pictures. 4000 pictures per second. 



F — Certain normallj- isotropic transparent materials become birefringent when 

 examined in a stressed condition under polarized light. Extended use of this 

 effect is made in the study of stress distributions in engineering structures and 

 in models of mechanical parts. High speed photography is now applied to 

 these photoelastic effects exhibited in a glyptol sample under impact stress 

 condition. This series of pictures shows impact testing of an unnotched glyptol 

 specimen in plane polarized light. 300 pictures per second. 



G — Poor contact conditions in rela>s ma\- give rise to improper circuit operation. 

 High speed motion pictures have been useful in the stud>' of contact chatter in 

 rela>s and other similar devices. This series of pictures shows normal operation 

 of contacts. 2000 pictures per second. 



H — This series of pictures exhibits contact chatter. In the first picture of this 

 series the movable contact spring is shown contacting the left fixed contacts. 

 In the second and third pictures, the movable contact spring has been drawn 

 against the right hand fixed contacts. At this point the current is cut off and 

 the movable contact springs return to normal as shown in the sixth picture. 

 Chatter occurs at this point with the movable spring returning to make contact 

 with the stationary contacts shown at the right. Two cycles of chatter condition 

 are shown. 2000 pictures per second. 



I — This series of pictures shows the No. 14 teletypewriter locking arm lever and 

 cam during overthrow which gives rise to noisy operation. They illustrate a 

 typical source of objectionable noise in apparatus of this type. Excessive clear- 

 ance between the cam and the locking arm lever is shown which results in impact 

 noise on the return of the locking arm lever. 1800 pictures per second. 



J — This series of pictures shows a modified No. 14 teletypewriter locking arm lever 

 and cam in which the overthrow has been eliminated with subsequent reduction 

 in noise. It can be seen that the lever arm now closely follows the contour of 

 the cam. 1800 pictures per second. 

 K — A knowledge of the fundamentals of speech and hearing is important to designers 

 of telephone apparatus. High speed motion picture photography has been 

 applied to problems associated with the production of speech by the vocal 

 mechanism. The pictures show vocal cords vibrating in production of speech 

 sound at a frequency of 120 cycles per second. Pictures of this type offer a 

 unique and practical means of securing much useful information relating to the 

 production of speech. 4000 pictures per second. 



L — At L is shown the action of the clapper striking one gong of an experimental 

 20-cycle ringer. This picture revealed more strokes of the clapper per second 

 of operation than was desired. This condition resulted in a peculiar acoustic 

 effect, readily explained from this series of pictures. 2000 pictures per second. 



