👉 A periodoscope is a device used to measure the frequency of light waves. It consists of two lenses, one at each end of the instrument, which focus the light onto a screen or a mirror. The lens in front of the first end reflects the light directly into the second end, where it is focused again onto a screen or mirror. This process repeats every 24 hours, which is why periodoscopes are also known as "periodic" telescopes.
