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Re: [Phys-l] method for measuring the size of the earth



David Bowman wrote:
I've come up with a fairly simple means of measuring/calculating
the size of the earth using only local measurements (not requiring
multiple sightings at far away locations like Eratothenes' method
needs).
The idea is to observe and time the motion of the terminator at
sunset/sunrise ascending or descending the face of a building...
David Bowman
Reading this work gave me an eerie sensation, akin to hearing from Harrison that he timed his chronometers by means of a star transit past a nearby building, and computed the ratio of day lengths proportionately.

The mind springs immediately to thoughts of a portable horizon, say 25 ft removed from the measuring stick, and leveled with a water manometer.
The acceleration would I suppose be reduced in proportion to the distances to the terminator, so that a vertical threaded rod carrying a photocell, driven by a servo (stepping motor) could track the terminator by its drive rate.
This note is certainly worth sharing with other instrument enthusiasts of various stripes.
David sometimes polishes his notes in a day or two, so I shall observe this pause.

BrianW