Oral History of Defence Electronics

R G Wells: The cinnamon resistor. The resistors were another problem. We found out that we could use the impurities in some of the tree wood and the bark, particularly cinnamon bark which was available by getting through the wire only about 2 feet, and we could normally pinch that while the Japanese sentry was moving around. We used a piece of string with the material rubbed on it from the burning of the cinnamon bark which had some impurities in it (we didn't have a chemical analysis); we weren't very fussed because most grid-leak resistors were about a megohm or thereabouts and we had no means or any way we could measure a megohm, so it was largely a trial and error thing to see if it would work. We made a number of these bits of string and tied them round different things to dry them out to get the thing going. Eventually about an inch, three quarters of an inch to an inch, was about the right order of things to get about a megohm resistance. They were the two main things.

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