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.
Few people realize the multiplicity and complexity of climates. It is a common occurrence for a prospective traveler or a business man to write to a meteorological establishment requesting, for example, a description of the climate of South America. Of course, no such thing exists. A continent does not have a climate, but a multitude of climates. Even to set forth, in general terms, the more important types of climate that prevail between Cape Horn and Panama is no small undertaking. Moreover, general descriptions often fail to supply the needs of those who make inquiries about climate.
Suppose, instead of the wholesale order above mentioned, the meteorologist receives the relatively modest request to describe the climate of Buenos Aires or Rio de Janeiro. Is it easy to comply with such a request? That depends. If the information is sought by a tourist who wishes chiefly to know whether he will need light or heavy clothing at a specified season, or whether his excursions are likely to be hampered by frequent rains, we can enlighten him in a few brief paragraphs. If the inquiry comes from a manufacturer who aspires to invade the South American markets, we must know, before replying, what kind of goods he purposes to export, and just how they are affected by climatic conditions. Are they liable to injury by high or low temperatures, dryness or humidity? Does the demand for them depend, as in the case of rubber coats, upon the prevalence of rain, or, as in the case of electric fans, upon the occurrence of hot weather during at least a part of the year? For each branch of the export trade certain elements of climate are important, and the more detailed and explicit the information that can be obtained about them the better. Suppose, again, climatic data are desired by a horticulturist who has to solve the problem of introducing a South American plant into the United States. In order to find the best environment for it in this country, he should know something about the climate of its original home. The data he requires are, however, different from those sought by the tourist or the manufacturer. Is the plant’s habitat a region where frosts occur? How long is the growing season? Is the rainfall rather evenly distributed over the year, or are there definite dry and rainy seasons? Such are some of the questions he will ask. For the purposes of medical climatology a different set of data will be sought. The astronomer, selecting a site for a new observatory, will ask about freedom from clouds, and also about the pureness and steadiness of the air that insure good “seeing.” The aviator will want information about winds and fog. And so on.
Thus it appears that climate means very different things to different people.
Climate has been variously defined as the sum total of weather, average weather, typical weather, etc., but the conception is still somewhat indefinite. We know that, while the weather of any place is subject to incessant changes, its climate persists; but we need not assume that it persists indefinitely. The geological record proves, on the contrary, that vast changes of climate have occurred in the course of long ages. In Antarctica and in Spitzbergen are found deposits of coal, constituting the débris of ancient forests such as could not exist in the climates now prevailing in those regions. There are plenty of other proofs that great climatic changes have taken place from one geological period to another; but what of changes in shorter intervals of time?