Until a thoroughly practical system of long-distance wireless telephony is developed, wireless telegraphy will remain the only possible means of communication between ships and shore, or between one ship and another, except where the distance is so small that some method of semaphore signalling can be used. In the days when wireless was unknown, a navigator was thrown entirely upon his own resources as soon as his vessel was out of sight of land, for no information of any kind could reach him. Even with a wireless installation on board, the captain of a vessel still needs the same skill and watchfulness as of old, but in the times of uncertainty and danger to which all ships are liable, he often is able to obtain information which may prevent disaster. In order to determine accurately his position, a navigator requires to know the exact Greenwich Mean Time, and he gets this time from his chronometers. These are wonderfully reliable instruments, but even they may err at times. To avoid the possibility of mistakes from this cause, wireless time signals are sent out at regular intervals by certain high-power stations, and as long as a vessel is within range of one of these stations the slightest variation in the chronometers may be detected immediately. Amongst these stations are the Eiffel Tower, giving time signals at 10 a.m. and at midnight; and Norddeich, Germany, giving signals at noon and midnight. These time signals have proved most useful also on land, more particularly for astronomers and for explorers engaged on surveying work. In addition to time signals, other valuable information is conveyed by wireless to ships at sea. A ship encountering ice, or a derelict, reports its discovery to other ships and to the shore stations, and in this way vessels coming along the same route are warned of the danger in time to take the necessary precautions. Weather reports are issued regularly from various shore stations in most parts of the world. The completeness of the information given varies a good deal with different stations, but in many cases it includes a report of the existing state of the weather at a number of different places, a forecast of the winds likely to be encountered at sea, say at a distance of 100 miles from land, and warnings of approaching storms, with remarks on any special atmospheric conditions at the time of sending. In Europe weather reports are issued daily from the Admiralty station at Cleethorpes, the Eiffel Tower, and Norddeich; and in the United States more than a dozen powerful stations are engaged in this work.