John Perkin gave short but interesting talks on 2 subjects: “The Equation of Time” and “Trilobites”.
John described his work on the calculation of the equation of time stimulated by his initial interest in the design of sundials. This determines the difference between local solar time (dependent on latitude) and “absolute” time, and is affected by the eccentricity of the earth’s orbit around the sun, and the obliquity of the ecliptic, plus other lower order factors.
John also spoke on a separate subject, namely trilobite fossils. These have a 3 lobed but diverse structure, and are found in the Cambrian, Ordovician, Silurian, and Devonian periods, where they were most widespread around 480 Myr ago. They then progressively declined through the Carboniferous & Permian periods, where a mass extinction occurred about 250 Myr ago. Their nearest living relative is the horseshoe crab.