1916] MEMORANDUM ON FOG SIGNALS 399 part of the work would be done at the Shore Station. A ship arriving near the land and desirous of ascertaining her position would make wireless signals at regular short intervals. The operator on land would determine the bearing of the Ship from which the signals came and communicate this bearing to the Ship. In many cases this might suffice; otherwise the Ship could proceed upon her course for a mile or two and then receive another intimation of her bearing from the Shore Station. The two bearings, with the speed and course of the Ship, would fix her position complete!}?-. I do not suppose that much can be done at the present time towards testing this proposal, but I would suggest that it be borne in mind when considering any change in the Shore Stations concerned. I feel some confidence that the requirements of liners making the land will ultimately be met in some such way and that they cannot be met with certainty and under-unfavourable conditions in any other. [1918. Eeference may be made to Phil. Mag. Vol. xxxvi, p. 1 (1918), where Prof. Joly discusses lucidly and fully the method of " Synchronous signals." In this method it is distance which is found in the first instance. It depends upon the use of signals propagated at different speeds and it involves the audibility of sounds reaching the observer through air, or through water, or through both media.]bserved with certainty at distances such as 10 or 20 miles.