Agricola 1556, p. 143:  A surveyor's orbis, from before the time of paper and scaled fields.

The Pulfrich Effect: Lythgoe (1938)

Lythgoe, R. J. Some Observations on the Rotating Pendulum. Nature, 1938, 141 (March 12 issue), 474.

The copyright on this work has lapsed.

Synopsis (no author abstract)

This was one of the few preWWII studies of the Pulfrich effect. The results are reported informally, as an "executive summary" for medical doctors.

Although he refers consistently to illuminance rather than luminance, Lythgoe does not describe his apparatus, so it appears that his results may not have taken variations of the natural pupil into account. Lythgoe's fit to his data led him to postulate an empirical equation for the Pulfrich latency difference equivalent to,

delta-t = 0.02 * [log10(IU/IL)] + const.,

with IU the upper (higher) level of illuminance. The formula seems meant to refer to photopic levels of illumination, only.

Lythgoe attempted to isolate the effects of target vs background as well as that of stray light, with mixed success. He reported a decline of the effect with time in dark adaptation, a result not confirmed in later studies. Systematic control for pupil size and point of fixation would have to await the work of Lit.

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