Two years into WWI Lawrence Bragg, an Australian officer in the British army, was sitting in a toilet situated just behind the British lines. The toilet had no windows and the door was closed, so the only effective contact with the outside world was the sewerage pipe that led directly to his bare bum. 400 meters away someone fired a British artillery gun. Suddenly he was lifted off the seat a few millimeters and dropped back down again. This had happened before, but this time the scientist had one of those rare moments of serendipity. He realised what caused it and more importantly, he could see how that knowledge could be applied.
Bragg, at 25 was the youngest person ever to receive a Nobel Prize, and was assigned the problem of how to locate the position of German artillery fire. If the Allied Powers could pinpoint a German gun battery, their guns could be trained upon it, rendering it silent. The methods used up to that point were ineffective, complicated and vulnerable to breakdown. Bragg had to do better. One of the problems with sound location, is that an artillery shell makes two booms, the first when the gun is fired and the second when the projectile breaks the sound barrier. As these are inevitably in different locations, merely listening for the sound of gunfire doesn’t work.
Bragg was fortunate to have on his staff another young physicist Corporal S Tucker who also had an inquiring mind. Tucker was having trouble sleeping. It wasn’t the German guns keeping him awake, it was a small hole in the tar paper lined wall next to his face. Every now and then a small blast of cold air would annoyingly burst through the hole onto his cheek. When the two men brought these stories together, they realised what was happening.
The sound of gunfire is loud, but a large part of the sound is entirely silent to human ears – it lies within the extremely low frequency range. It was this burst of low frequency energy that lifted Bragg’s bare bum off the toilet and blasted Tucker’s face.
The two men secured an old ammunition box and drilled a small hole in one end. They then positioned a platinum wire inside the box over the hole and passed a low electric current through the wire which warmed it up. This was then connected to a device that measured the resistance in the wire. When a gun was fired, a low frequency wave pushed air through the hole, cooled the wire, changed its electrical resistance which showed as a sudden dip in the gauge. All they needed to do was to have two of these devices and move them around until the dip in the gauge was greatest, transpose the angle of each box onto a map and the German battery was located. This method was accurate to between 25 – 50 metres.
From that point on, German artillery became much less effective and a much more dangerous posting. If his discovery ended there, that would be enough to assure Bragg of his place in scientific and military history, but it didn’t. Bragg’s father was also a scientist and when he spoke to his son about his microphone he realised that it had an application in a problem he was facing for the British Admiralty. How to find submerged submarines. In 1940 Hitler’s Atlantic blockade began to bite, German U-Boats were sinking freighters at an alarming rate and the code-breakers of Bletchley Park were yet to crack the Nazi Naval Code. Lawrence’s father, Sir William Bragg developed an underwater range finding device then called ASDIC, and now referred to as SONAR. Anyone who has ever seen a submarine movie, from Das Boot to Hunt For The Red October, will be familiar with the PING…PING sound used to find and destroy enemy submarines. Even when Allied destroyers were told by the codebreakers where in the Atlantic to look for
submarines, it was that PING PING that pinpointed the location and made being a German submariner a very dangerous occupation indeed.
So, you can see how the course of two world wars were changed by one scientist’s bare bum and another’s interrupted sleep,
(c) 2018 Paul Hannah