Fernez's separate goggles didn't allow a dive deeper than ten metres because they were not pressurised, so as the diver went deeper the goggles were squeezed onto his face and eyeballs by the increasing water pressure, a phenomenon known as "mask squeeze". In 1933, Le Prieur replaced the Fernez goggles, noseclip and valve by a full face mask, directly supplied from the air cylinder, which balanced the pressure in the mask with the external water pressure. Le Prieur remarked that the diver could breathe through the mouth or nose, or both, at will, and that it was even possible to speak with another diver by bringing the glass close to their ear, the glass forming a microphone.