Under the worst conditions this wonderful parachute can be relied upon always to open and carry its load at a height of only one hundred feet, and its use is safe in all circumstances when dropped from two hundred feet above the ground. After it has once got into operation and taken charge of affairs, so to speak, the man descends at the rate of only fifteen feet per second, which is just about the same as dropping from a height of a little over three feet. In other words, he will arrive on the ground with no worse bump than you would get by jumping off the dining-room table. But suppose that there were a wind blowing: would not the parachute come down in a slanting direction and then drag the man along? Or may he not alight upon a tree or the roof of a house, only to be pulled off again and flung headlong? Quite true he might, were not proper provision made for such occurrences. Embodied in the harness is a lock which can be instantly undone, by a simple movement of a lever in the hand, and by its aid the man on touching earth or on alighting upon anything solid can release himself instantly, after which the parachute can sail away whither it will, but he will be safe and sound. What Mr. Calthrop has accomplished by the invention of his "Guardian Angel" parachute may be summarised briefly by saying that he has reduced the minimum height from which a parachute could be dropped from two thousand to two hundred feet, and that he has made it possible to launch a parachute, with the certainty of safety, from any kind of aircraft flying at the slowest or highest speed of which they are capable. * * * * * You are only a boy now, but when in years to come you are quite old and have grey hair you may become a Member of the Air Board and--who knows--it may become your duty to decide that this great invention shall be always used on the training grounds to save the lives of the young men, not yet born, who are then learning to fly. During the War, one was killed every day, 365 in a year, many of whom might have been saved had more "Guardian Angels" been in use. INDEX Acetone, 36, 57, 58 Acetylene, 58 Aeroplanes, types of, 285, 286 Air-raft equipment, 89 Alcohols, 49, 50, 51, 52, 55, 139 Aluminium, 157 Anchors for floating bridges, 80 Anti-aircraft guns, 119 _Aquitania_, s.s., 197 Armourer, 17 Austrian heavy mortars, 111, 114, 117 Bamboo, bridges made of, 87 Basic steel, 101 Becquerel, H., 40 Benzene, 35 Bessemer, Sir Henry, 93, 98, 99, 100, 102 Blast-furnace, 94, 95 Boilers in warships, 176 Breech-block of guns, 131, 132 "Brennan" torpedo, 219