Catching the Waves - Neil Johnson's 1999 Christmas Lectures 2/5

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In his second Lecture, Neil Johnson explores how oscillations of sound or light can define a unit of time. Watch all the lectures in this series here: https://youtube.com/playlist?list=PLbnrZHfNEDZyajvliVTMxSLGo1rCkl6vY&si=Mpn9fggqAwh6TYrF Watch our newest Christmas lectures here: https://www.youtube.com/playlist?list=PLbnrZHfNEDZyQJZLPMjwEoOLdkFBLU2m1 This was recorded on 2 Dec 1999. -- This year marks 200 years of the Royal Institution Christmas Lectures — a world famous series showcasing science, curiosity, and mind-blowing demos, and started by the legendary Michael Faraday himself. To celebrate, we're unlocking the archive. Every Saturday, we’ll upload a classic lecture to our YouTube channel — some not seen since they aired on TV. Sign up as a Science Supporter and get early access here: https://www.youtube.com/channel/UCYeF244yNGuFefuFKqxIAXw/join -- From the 1999 programme notes: Early clocks relied on the flow of some substance, such as water or sand, to measure the flow of time itself. However, there is nothing around us that can flow evenly enough to measure time accurately. It was later realised that a more reliable method would be to use "inverse time", in other words oscillations or waves. If we could find a system with some natural oscillation period, then an agreed number of these oscillations could be counted in order to define a unit of time. One such system which was used early on is the swinging pendulum. In fact this dependence on oscillations, as

Published 2026-02-11 · Watch on YouTube ↗
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