It is a commonplace of conversation that for some months past the weather conditions have been abnormal, particularly in the matter of rainfall, in the battle-zones and elsewhere. Detailed data from regions close to the firing lines are not available; and we have only general statements of inclemency in so far as they affect military operations. But in districts not far away,—the British Isles, for instance,—the records of excessive raininess during the winter of 1914-15 and at subsequent times have not escaped comment; and others besides meteorologists are discussing the possibility of a connection between the heavy cannonading and the rainfall. The professional meteorologist is called upon to answer whether there is any rational explanation of what appears to be a marked departure from the usual sequence of weather conditions. Is it possible that the tremendous expenditure of ammunition—an expenditure which the layman may well regard as an experiment in concussion sufficiently vast to be decisive—has facilitated condensation and its later stage, precipitation? In concise terms, has the bombarding not only caused clouds but forced the clouds to send down rain?
It is conceivable that such could be the case; and stranger things have happened than the revelation through war of fresh progress in man's effort to comprehend and master the processes of Nature. And here, as is so often the case, Nature herself has suggested the relation, for we have all noticed that after an exceptionally near and heavy clap of thunder, the raindrops fall with a rush, as if the very tumult had shaken the clouds and caused the downpour. Later we shall see how this well-known phenomenon is to be interpreted.
Three separate lines of inquiry suggest themselves as throwing light on the problem. First, the underlying principles of the formation and flotation of a drop of rain; second, the causes of excessive rainfall in certain places at certain times; and third, the direct relation, if any, which exists between the use of high explosives and showery or rainy weather. To most of us the raindrop is an ordinary, commonplace drop of clean water, or rather it seems to be clean. It is one of the most common phenomena of everyday life, and most of us never stop to think that its life-history could be eventful; in fact we are sure that there can be nothing unusual about a drop of water falling through the air. On the contrary there is much that is wonderful in the wanderings of the little visitor; and the structure of each minute globe is in its way as marvelous as the structure the great nebula in Andromeda.
Probably no two raindrops are exactly alike. Photographs of snow crystals make it plain that no two flakes even in the same storm have identical shapes and structures. Raindrops are formed under somewhat similar conditions of strain, with forces more energetic, but never quite permanently balanced. Drops change incessantly, even those that seem to be quiescent. Many have made long journeys and undergone modification at every turn of the road; but large or small, each globule is a complex of ionic infinitesimals wrapped in a blanket of water vapor. It is an elastic blanket, beyond measure, and changes its size and sometimes its form, with every variation in pressure, temperature, and electrification. The process of wrapping the ions in the blanket of vapor still baffles science, although man has had recourse to certain small messengers, waves of light, wave-lengths little larger than a millionth of a millimeter, and sent these among the ions to do his bidding.
Generally speaking, a raindrop or any water-drop is an aggregation of hydrogen and oxygen atoms combining in the value of two to one. In a gram of hydrogen (that is, about fifteen grains), there are six million million million million atoms. But still smaller than atoms are these carriers of electric charge called electrons, oscillating many million times per second and as constantly colliding with one another. An English physicist who has worked much along these lines, once said that unless we had a better test for a man than we have for an unelectrified atom we could never detect that the earth was inhabited.
But larger than the electrons are certain foreign bodies called nuclei or centers of condensation; and if ever man succeeds in making rain artificially it will be by increasing the number of nuclei. In fact, the vortex guns or smoke-ring firers used in the grape growing regions of the West to dissipate hail have a certain scientific value in that they furnish nuclei at critical times. Notwithstanding the belief of the vineyard owners, however, the efficacy of these Steiger guns remains unproved. Without nuclei, condensation does not occur even when space is saturated with vapor. And here a word of caution, and a bit of information that rain-makers in general do not know. While textbooks speak of the capacity of air for vapor, they overlook the fact that it is space rather than air which contains the vapor, for air and water vapor are two separate entities and must be considered as such.