This provides an unsharp signal which is added in opposite polarity to the 
main signal previously discussed. The composite signal thus obtained simu- 
lates the effect of unsharp masking, designed to edge enhance by increased 
contrast the image outlines. 
The Ultrasonic cell is a fluid filled glass vessel with a crystal on 
the bottom and damping material on the top. The modulated input signal 
causes the crystal to oscillate producing a density pattern in the fluid 
which acts as an optical diffraction grid. The amplitude of the oscillae 
tions détermines the degree of diffraction obtained. A bar-slit system 
utilizing the effect of diffraction, modulates a beam of light in accorde 
ance with the variable amplitude of the cyrstal oscillations. In this 
manner the picture elements are scanned, transduced, and faithfully repro- 
duced with an appreciable range in density. 
A discussion of the functional characteristics of the Electronic Rec- 
tifier system can best be described by reviewing the system schematic in 
Fig. #4. In the Electronic Rectifier, the recording cylinder revolves at a 
constant rate of 500 rpms. The rotation of the recordingcylinder is directly 
coupled to the scanning motion of the oscillating mirror, For each rotation 
of the recording cylinder, one scan line is performed, Since the diameter 
of the recording cylinder is fixed, the required scale change from one scan 
to the next, is accomplished by varying the angular velocity of the scan- 
ning mirror, If the angle of scan is increased, the speed of scanning the 
negative copy is higher and the recorded line is thereby reduced in length, 
A mechanical analog computer shown as computer #1 in Fig f/; solves the 
Spread through a number of years.