 Complete the following phrase:  The suit is made out of rubberized canvas. The helmet, for the first time, includes a hand-controlled exhust valve that the diver uses to evacuate his exhaled air. The valve included a non-return valve which stops water from entering the helmet. Until 1855 diving helmets were equipped with only three circular windows front, left and right sides. Cabirols helmet introduced the fourth window, in the upper front part of the helmet, which gives the diver an upward view. Having been presented to the 