Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

on to the rubber collar by wing nuts, and thus clamp the collar watertightly to the corse- let. The neck of the corselet has a segmental screw ring- (an interrupted screw thread) on which the helmet, which has a corresponding ring, is screwed securely by one eighth of a turn ; a recessed washer makes the joint quite watertight. Two studs in the front of the corselet are for the metal clips of the weights to take over, but some divers do not use these, preferring to use slip-lines for the weights. I he 6-bolt Corselet has only two metal straps (of a stronger description than those of the 12 and 8-bolt corselets), these being recessed on the under side to take ribs which are formed on the indiarubber collar of the dress. As in the case of the 12-bolt helmet, the clamping is done by means of wing nuts. Helmet.—The helmet, which is of tinned copper, is, as already mentioned, fitted with a segmental ring at the neck corresponding with that on the corselet. A small stop, or pin, is provided at the back of the helmet which is turned down into a recess on the corselet as a precaution against the helmet unscrewing. 1 HREE strong flat glasses, half an inch thick, are fitted in brass frames in the helmet ; those at the sides being oval and protected with brass guards, the front glass being circular; the latter can be unscrewed, enabling the diver to gi\e orders and get fresh air without removing any other part of the dress, or if he has to come up for a rest, the whole helmet may be unshipped by one-eighth of a turn. Sometimes an additional window is fitted at the top of the helmet, to enable the diver to look up- ward without bending his body back. Fig. No. 14. Inlet Valve (Fig. No. 14).—The air from the pump enters the helmet through the non-return “inlet valve,” the outer end of which has a male thread to which the air pipe is screwed. The inlet valve consists of a metal disc and spindle which is pressed on to a coned metal seating by a light metal spring. Air coming in from the air pipe can easily over- come this spring- and lift the valve, but none can pass backwards from the helmet to the air pipe. The object of this arrangement is to prevent injury to the diver in the event of his air pipe being injured some distance above his head, or the pump becoming so seriously damaged as to fail to maintain a pressure. If either of these things happened the pressure in the air pipe would fall considerably, and if there were no non- return valve on the helmet the highly compressed air in the latter would escape up the 26