RAIN-GAUGE, or PLUVIOMETER, an instrument which measures the depth of the rainfall. In its commonest form it consists of a cylindric vessel closed at the top by a funnel shaped lid, through a hole in the centre of which the rain falls. A narrow glass tube, raising outside the vessel from near the bottom, shows by the height of the water in it the height of the water in the vessel itself. A very simple rain-gauge consists of a copper funnel, the area of whose opening is exactly 10 square inches. This funnel allows the rain to pass into a bottle, and the quantity of rain caught is ascertained by multiplying the weight in ounces by 0.173, which gives the depth in inches. The Weather Bureau at Washington has perfected several forms of rain-gauge for more accurate observation. One of these weighs the water as it accumulates in the receiver and records regularly the gain in weight on a moving strip of paper. In regions where the rainfall is very slight there is a demand for gauges that will record the entire fall for a month or three months, and such have been made to meet these special demands. As a rain-gauge is nearer the ground it is found to indicate a greater rainfall. This is partly due to the cold rain drops getting larger in falling through the very moist air near the ground and partly to the greater occurrence of eddies about the gauge at greater heights. Hence, when the rainfall at two places is to be compared, the gauges ought to be similarly situated. A rain-gauge must be placed in as open a position as pos sible, out of the way of houses, trees and similar objects that may deflect the falling drops.
The problem of rain making, or bringing rain from the clouds in a season of drought, has in all ages been of the greatest interest to humanity, as lack of ex pected rain has assisted in producing many famines and the loss of many millions of lives. Attempts have been made to bring rain by ap peals to Divine Providence in prayer in Chris tian countries, while the ignorant heathen prac tise various forms of fetishism, and even offer up human sacrifices with the same object. Owing to the large extent of arid lands in the United States the question of bringing about rain by scientific processes has often engaged attention. It was noted that for est fires have often been followed by rain, and in 1834 James P. Espy of Pennsylvania proposed the building of enormous fires in the regions where rain was desired to bring about the needed showers. This was re
garded as impracticable both in America and in Australia, where it was •also suggested. That great battles, and sometimes lesser ones, attended by cannonading, were occasionally fol lowed by heavy rainfalls has long been a popu lar belief, and this gave origin to the opinion that explosions similar to those of artillery might bring about rain in a season of drought. This belief did not apparently take into ac count the circumstances that important battles are usually fought in temperate regions, with normal rainfall, and where a disturbance of the atmosphere might easily bring a downpour from the skies. It is also averred by the opponents of this theory that the number of battles fol lowed by rain has been comparatively small; and we now know that the tremendous quanti ties of explosives used in the World War had no appreciable effect on rainfall. In 1891, how ever, Congress made an appropriation for a series of experiments in Texas, which were conducted by General Dyrenforth for the De partment of Agriculture. There has been much controversy as to the effect of these experi ments which were conducted on the theory of provoking rainfall by concussion caused by ex plosions, giant powder being the explosive used. General Dyrenforth claimed that the experi ments were entirely successful, that the drops sometimes commenced to fall within 12 seconds after the initial explosion, and that °the con cussions from explosions exert a marked and practical effect upon the atmospheric conditions, in producing or occasioning rainfall, probably by disturbing the upper currents.° On the other hand, Prof. A. H. Hazen, basing his views on the newspaper reports of the experiments, argued that there was no evidence whatever that any rainfall had been produced by the ex plosions, while W. K. Curtis, M.D., who was with the Dyrenforth party, substantially con firmed Professor Hazen's view, and declared that rain fell before the experiments had be gun. The weight of evidence was generally accepted by the public as supporting the views of Hazen and Curtis, and while the theory that rain frequently follows aerial explosions has not been wholly abandoned, no serious efforts have been made to follow up the experiments of General Dyrenforth: See Mrrsoaotocv.