Dutch navy testing diving device and under water telephone according to the Dutch magazine Marineblad dated 1888-1889 no. 7

An item reported that in the (wet) dock of the naval shipyard at Willemsoord in last December a diving device of the firma Denayrouse was tested. It mainly concerned a new improved simplified helmet buckle and a telephone system Adèr for communication in water. Both inventions performed excellent and the intention was to purchase some examples for further tests.