Of all the sounds that haunt the air, probably the most mysterious are those which are best called by the generic name “brontides” (coined, in the Italian form _brontidi_, by Prof. Tito Alippi from two Greek words meaning “like thunder”), though they rejoice in scores of other names in various parts of the world. Brontides take the form of muffled detonations, resembling the sound of distant cannon or peals of thunder, and are heard chiefly in warm, clear weather. The first systematic investigations of these phenomena were made in India. The fact that they were frequently reported from the neighborhood of Barisal, a town in the Ganges delta, led to their being called “Barisal guns,” under which name they were first made known to European science in 1890. A few years later they were discussed in an extensive memoir by E. van den Broeck, who had collected numerous reports of their occurrence in Belgium, especially on the seacoast, where they are known as “mistpoeffers” (i. e., “fog belchings” or “fog hiccups”). The majority of descriptions, however, have come from Italy, where the sounds appear to be extremely common, though peculiar to certain localities, and where they bear a great variety of names. In Australia the noises are called “desert sounds,” in Haiti, “gouffre,” etc. They have been reported from parts of the United States, including California and, above all, from the vicinity of Moodus, Conn., which owes its original Indian name, Morehemoodus (“place of noises”), to the brontides which appear to have formerly been much more common there than they are to-day. There is a reference in one of Lord Bacon’s works to “an extraordinary noise in the sky when there is no thunder”; apparently a description of brontides. The source of these sounds is undoubtedly subterranean in a great many cases, though perhaps not in all. Prof. W. H. Hobbs, who has made a painstaking study of the seismic geology of Italy, concludes that the brontides of that country are due to the slow settling of the blocks of the earth’s crust; a process which, in its more abrupt and violent phases, causes definite earthquakes. Alippi believes that in order that the sounds may be heard they must be reenforced by a peculiar configuration of the ground, above or below the surface, and he attaches special importance to the effects of caverns, which he suggests act as resonance boxes in the production of audible brontides. Occasionally an apparent brontide may be due to the explosion of an unseen meteor. Lastly, a certain proportion of these thunderlike sounds, if not merely distant thunder, may be such noises as cannonading, blasting, or the like, made audible at unusual distances by the refraction of sound waves. CHAPTER XII CLIMATE AND CLIMATES Some day the meteorologists of the world will join forces to produce a great encyclopædia of climate. No work of science is more sorely needed, but the magnitude that it would, ideally, assume is simply staggering.