The oxygen equipment has already been fully described by Mr. Unna in the _Alpine Journal_, vol. xxxiv., page 235. The apparatus is, in principle, quite simple. It consists of a frame carried on the shoulders of the climber, at whose back, in a rack attached to the frame, are four steel cylinders filled with oxygen compressed to 120 atmospheres. From the cylinders the oxygen is taken by means of copper tubes over to an instrument arm in front of the climber. This instrument arm, also attached to the frame, carries the pressure gauges and so forth which indicate how much oxygen the climber is left and how rapidly the supplies are being used up. Close to the instrument arm and readily accessible are the valves necessary for controlling the rate of flow of oxygen from the apparatus. From the instrument arm the oxygen passes through a flexible rubber tubing up to a mask covering the face of the climber. The two types of mask supplied to the Expedition proved useless, partly owing to their stifling effect upon the wearer, and partly to the fact that saliva and moisture collected rapidly under them and froze. Both, therefore, had to be discarded, but fortunately I was able to make a substitute which functioned successfully. This mask consists of a rubber tube into which is let a rubber bladder by means of a glass T-piece, or by means of two straight pieces of glass tube let in at opposite ends of the bladder. One end of the rubber tube is fastened to the tube of the apparatus out of which the oxygen flows, the other end being held in the climber’s mouth. On exhaling, the climber closes the rubber tube by biting upon it, and the oxygen issuing from the apparatus, instead of being wasted, is stored up in the rubber bladder. On inhaling, the pressure of the teeth is released sufficiently to allow the rubber tube to open, thus permitting the oxygen stored up in the bladder to flow into the climber’s mouth, whence, mixing with the air exhaled, it is drawn into the lungs. The chief advantages of this mask are that, firstly, it economises oxygen to the greatest possible extent, and secondly, the swelling and the shrinking of the bladder during each exhalation and inhalation respectively give the climber a fair idea as to how rapidly the oxygen is flowing from the apparatus, and thus enables him to keep a check upon the readings of the flow-meter, or instrument which indicates the rate of flow of gas. In actual practice it was found that in the space of a few minutes the climber used the mask quite automatically. The biting upon and closing the rubber tube and subsequent opening were performed without mental effort.