GRAPHIC RECORDING OF SPEECH VIBRATIONS 91 
whose initial deflection is obtained by refraction as it passes 
through free sound-transmitting air. The purpose is to develop, 
if possible, an apparatus combining great sensitiveness and high, 
magnification with minimum distortion, and constructible at 
moderate expense in the average laboratory of limited means 
and equipment. 
The sonoscope. The principle of the sonoscope is shown in 
three forms in figures 1, 2 and 3. It consists essentially of a 
receiver horn H, with a thin mirror-diaphragm D (probably of 
silvered glass or mica, or perhaps of polished metal) from which 
P 
Fig. 1. Principle of the Sonoscope, Form A (Horizontal Section) 
a ray of light (or light-lever) R is reflected to the demonstration 
screen or photographic film P. The ray is received through the 
pinhole aperture A, focussed by the lens Li, falls at an oblique 
angle (say 30 degrees) on the vibrating mirror-diaphragm, whose 
varying vibratory positions DD' shift the ray to varying paths 
RR'. These paths are nearly parallel or slightly divergent with 
an extreme separation of perhaps 0.005 or 0.010 of an inch, 
more or less, according to the amplitude of vibration which 
If either of these principles proves successful, acknowledgment will be due 
to Prof. D. C. Miller, as the ideas were partly suggested to me by the phonodeik. 
