a
Upon arrival of the shock,
the switch closes and sends a
signal to a distant receiving station by cable or radio,
procedure has been found to be rather expensive and,
This
thus,
it
has been replaced by the method of rocket-trail photography.
In passing through a region occupied by a shock front,
light is refracted so that objects seen through the shock wave
appear to be distorted.
This fact permits
arrival to be determined,
times of shock
Just prior to the explosion, 4
fan-like gird of vertical smoke trails is produced from
a
nunber of rockets launched from the ground at various distances
from the zero point.
motion-picture camera,
These
trails are photographed with a
The arrival of the shock front ct a
point between the camera and any trail is indicated by an
apparent shift in the position of the
- 15 -
trail due to refraction.
Attachment "B"