Figure 7. E. von Petersen's photometer. Left: device before opening. Middle:
device during exposure. Right: device after closing. This device was invented
in 1886 by Eugen von Petersen, an engineer at the Naples zoological station.
The design follows the specifications of Carl Chun. The first test of this ins
trument was by Carl Chun off Capri in 250 meters water depth.