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Figure 5. P. Regnard's combination photometer and photometric recording device.Invented by Paul Regnard in 1888 for measuring the intensity and duration of liglight with increasing depth. It was used by Prince Albert aboard a steam tug offFunchal at depths of 20, 30, and 40 meters. The balloon pressure device was not part of the original instrument but added afterwards. (Image credit: Oceanographic Museum of Monaco | P. Roggero)