The Pulfrich Effect: Galileo's Try at the Speed of Light

Galileo 1638, p. 14:  An apparatus to measure the strength of a vacuum.

In the posted passages, notice that the method of Galileo suffers from lack of accommodation to the gross differences between the reaction times of human beings (on the order of 10-1 second) and the transit time of light over a distance of kilometers (on the order of 10-4 second).

Although Galileo makes no explicit statement concerning personal equation, his method of practising at short distances before measuring at long distance would impose experimental control cancelling each observer's personal equation nicely. Such control would be equivalent to simple subtraction of an astronomer's personal equation, after estimation of the equation experimentally, independent of the recording of the observation.

Of course, in astronomy, one rarely would have an opportunity meaningfully to practice ones observing skills at close distance from an object of interest.

Comments on Measuring the Speed of Light: Galileo (1638)

Note: Copyright on the original work and the translation herein has expired. The passages posted below are in public domain.

Galileo 1638, p. 7:  The tensile strength of any  column is finite.

Text of Passages on Translator's pages 42 - 44:

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The Pulfrich Effect, SIU-C. Last updated 2000-07-23