The boat dives at dawn, and, the trim correct and the captain satisfied, the order is given to "fall out all but diving hands." One officer remains at the periscope, while the remainder and the majority of the crew move off to their sleeping billets and lie down. When not on watch it is customary for everybody to sleep, read, and eat all the time; this is to conserve the stock of air in the boat. Oxygen is not carried, but "purifiers" are. The air in the hull of the boat is, however, ample for a long day's dive, and except when kept down by accident or the machinations of the enemy there is no necessity to renew it. It is kept on the move, however, by ordinary circulating fans, which produce a general draught and disturbance of the halos of bad air around each man's head, and this keeping of the air moving makes a great difference--in fact, with no fans running a match fails to burn after nine hours' diving; with all fans circulating a match can be lit after a dive of from fourteen to eighteen hours. Why this is, I don't know. If any work is done while diving (such as reloading of tubes or repairing of damage) the air is used more rapidly--in fact, extraordinarily quickly. When no work is being done, but only the usual day's dive has been carried out, there is a slight increase in rate of respiration among the hands on watch, with a slighter rise in rate of pulse. But as soon as one attempts to do anything, such as lifting weights or making a speech to the crew on the subject of their crimes, one finds it necessary to breathe heavily and quickly; and in fact, in the case of the speech, only a few minutes' harangue would be possible towards the end of a day. Officers do not keep watch at the periscope for more than a couple of hours at a time--it is bad for the eyes and bad for the temper; the deadly monotony of shuffling slowly round while stooping to stare at a perfectly blank and usually misty horizon is the worst part of a patrol. The periscope work makes one sleepy also. Submarine officers sleep a lot; the work is dull and sleep passes the time. One gets tired of reading, although one certainly reads an extraordinary amount. A succession of blank uneventful trips is good for education, however; somebody once said that the book to be cast away on a desert island with was Gibbons' 'Roman Empire.' I have known heavier books than that to be worked through on patrol--even to weighty tomes on Constitutional History. The sailors also read, sleep, and eat continuously. A few hands keep watch on the hydroplane wheels, the pumps, and the motors; the rest take it easy. They study such periodicals as one finds on the counters of small tobacconists' shops, and in addition they borrow and read intelligently the more abstruse literature from their officers' library.