The scientific study of fog signals, dating especially from Tyndall’s well-known investigations at the South Foreland, in England, in 1873, and those of General Duane and Professor Joseph Henry in America, begun somewhat earlier but continued contemporaneously with Tyndall’s, has probably raised more questions than it has answered. The caprices of these signals take the shape of variations in the range of audibility--a signal may at one time carry 10 miles and at another only 2--and the formation of “zones of silence,” comparatively near the signal, within which the sound is not heard though audible at much greater distances. The silent zones are sometimes more or less permanent and are then generally due to peculiarities of topography; but in many cases they are transient and opinions differ as to their cause or causes. Since it is only when fog prevails that fog signals are sounded (except for experimental purposes), and that vessels meet with accidents on account of the failure to hear such signals, the idea has become rooted in the public mind that these acoustic eccentricities are entirely due to fog. When, however, experiments are made in clear weather, similar phenomena are observed. In foggy weather audibility is often better than the average, because fog prevails chiefly when the air is still and of uniform temperature, and such conditions favor the transmission of sound. Tyndall strongly denied that either fog or falling rain, snow, and hail have, as has been commonly believed, a muffling effect on sound, and he attributed the peculiar behavior of fog signals to the presence in the atmosphere of invisible “acoustic clouds,” consisting of patches of air containing irregularities of temperature and humidity. To the same cause he ascribed the occurrence of mysterious “aerial echoes,” not due to any visible object. Several recent investigators have disputed these conclusions. Thus it is asserted that when the fog signal is in fog and the observer in a clear atmosphere, or _vice versa_, or when the signal and the observer are in different fog banks, the fog reflects the sound very strongly. Apart from the possible effects of fog itself, the very extensive investigations made by Prof. L. V. King, of McGill University, at Father Point, Quebec, led him to conclude that the effects are chiefly due to eddies in the atmosphere. Prof. King used in his observations the latest devices for obtaining exact measurements of sound and such up-to-date meteorological apparatus as pilot balloons for measuring the wind at various levels. He discovered, among other things, that existing types of fog-signal machinery are very wasteful of energy, and he has pointed out how their “acoustic efficiency” may be much improved. Before we dismiss this subject it should be noted that submarine bells and the radio compass have made mariners much less dependent than they formerly were upon the types of signals that are affected by meteorological conditions.