The combined chart-room and navigation compartment was spacious in extent, but considerably congested with an intricate array of levers, telephones, indicators, switches, and a compact wireless cabinet. In the centre was a table with clamps to hold a large-size chart. Right "in the eyes of the ship" was a gyroscopic compass, which, by reason of the needle pointing to the true, instead of the magnetic, north pole, greatly simplified steering a course, since those complicated factors, variation and deviation, were eliminated. Altimeters, heeling indicators, barometer, thermometer, and chronometer, with other scientific instruments, completed the equipment of the room, which was in telephonic communication with every part of the airship. From the car the three men ascended to the interior of the envelope, climbing by means of aluminium rungs bolted to the flexible shaft. Once inside the rigid envelope, it was possible to walk the whole five hundred feet length of the airship along a narrow platform. From the latter crossways ran at frequent intervals so that access could be obtained to any of the ballonets. The interior reeked of the strong but not obnoxious fumes of the brodium. "Leak somewhere," remarked Kenyon, sniffing audibly. "Yes," agreed Fosterdyke, "one of the supply pipes gave out this morning; otherwise you wouldn’t know by the sense of smell that the envelope was fully charged." He struck a match and held it aloft. It burned with a pale green flame. "I wouldn’t care to do this with hydrogen," he remarked. "Non-inflammability of the gas practically does away with all risk. When you recall the numerous accidents to aircraft in the earlier stages of the war, you will find that in over eighty per cent. they were caused by combustion. Of course I’m referring to disasters other than those caused directly by enemy action. Now, carry on; up you go ... no, hold on," he added, as a bell rang shrilly just above their heads. "One of the workmen coming down," said Fosterdyke. "Opening a flap at the top of this shaft automatically rings an alarm, otherwise anyone ascending might stand the risk of being kicked on the head by the feet of someone else descending." "By Jove! I know that chap!" exclaimed Kenyon, after the mechanic had descended the long vertical ladder. "Yes, it’s Flight-sergeant Hayward," added Bramsdean. "He got the D.C.M. for downing two Boche ’planes over Bapaume."