Archibald Montgomery Low 141 



of the light-sensitive selenium cell. By shining a light on 

 a certain portion of a door it is possible to unlock and 

 swing open the door, untouched by human hands. The 

 explanation is simple. Inserted in the door was a selenium 

 cell. When under a ray of light its electrical resistance 

 altered, and this change in turn operated a catch and 

 caused the door to swing wide. 



Just as baffling to the uninitiated, and more valuable 

 scientifically, was a method of photographing air-cooled 

 engines by invisible heat rays which the Professor 

 developed, thus enabling local overheating of the engine 

 to be discovered while the engine was actually running. 

 Other experiments which he carried out had for their 

 object the increasing in efficiency of artificial light — at 

 present only about 2 J per cent, of the possible light is 

 actually ' trapped ' and used, a striking instance of the 

 embryonic state of our scientific knowledge. 



Inventions such as these, however, are little more than 

 the Professor's hobby. His real achievements have been 

 in the fields of scientific research connected with internal 

 combustion (motors), wireless, and sound. 



Professor Low was the first man to take a photographic 

 record of sound. This he did by means of an instrument 

 called an audiometer, which records faithfully the 

 strength of every sound coming into contact with the 

 sensitive diaphragm inside it. The diaphragm has a 

 very small mirror attached, reflecting a tiny beam of 

 light on to a strip of photographic paper. The paper is 

 traversed on a slide, and as it moves the beam of light 

 traces an area which is increased or reduced as the sounds 

 are intensified or softened. Silence is registered in a 

 straight line; thus the degree and type of divergence 

 from the line reveals the amount of sound photographed 

 and its characteristics. 



This machine was used during experiments carried out 

 a few years ago as part of an attempt to reduce the noise 



