. . .it's probably worth carefully noting that resonance effects can take place through almost unbelievably subtle mechanical linkages. I've been reading 'Tuxedo Park' which is a biography of Alfred Lee Loomis, who financed (among other things) the American research effort that led to the invention of radar. Loomis was fascinated with precision horology and one of the set-ups in the laboratories he owned included three Shortt clocks, all installed underground on massive rock piers that were part of the underlying bedrock. He also ran a landline from his lab in Tuxedo Park, where the Shortt clocks were installed, to Bell Laboraties in New York, fifty miles away, in order to use the 1K hz quartz clock at Bell as a master signal for the chronograph he was using for timing trials on his Shortt clocks. He did a lot of interesting experiments, but for our purposes one of his most interesting findings was that the Shortt clocks, even in a vacuum, isolated from each other by huge masses of solid rock, still managed to transmit enough vibration to each other to create resonance effects:
"Loomis set up such an accurate system of precision clocks and comparative time recording that he was able to register infintesimal fluctuations in the clock rates due to the fact that the pendulums coupled and influenced one another despite all the precautions taken against disturbances. Describing his test at the winter convention of the American Institute of Electrical Engineers in January 1932, Loomis said, 'This would seem to sho9w that, massive as the piers have been made, they are not infinite in comparison to the fourteen-pound pendulums, and that the strains are set up by each pendulum that are felt in some degree by the others through the piers and solid bedrock.' He found that when he placed the clocks at the the corners of an equilateral triangle, facing inwards, the coupling was broken. . ."
- Tuxedo Park (paperback edition, p. 69)
Not bad for 1932 . As I read through the other posts in this thread it seems clear that coupling of two oscillators can occur through a variety of mechanisms, any of which (airflow, air drag, vibrations through the plate, linkage of the balance springs) might plausibly be described as resonance depending on how narrowly the term is defined.
Thanks again,
Jack