RAIN-MAKING FAILS

Sun (Auckland), Volume III, Issue 774, 21 September 1929, Page 32

RAIN-MAKING FAILS

SPRAYING CLOUDS WITH LIQUID AIR DIFFICULTIES TOO GREAT Severe drought prevails in HongKong, and according to a report in “The Times,” an attempt has been made to alleviate it by artificial means. Air Force pilots, acting in consultation with the Observatory, have dropped powdered kaolin on the clouds, in the hope of persuading them to shed rain. The results, we are told, have been “most meagre.” This should not be surprising, writes the meteorological correspondent of the “Observer,” in view of the scanty measure of success that has attended similar experiments in the past. From the earliest times man has sought in vain to master the elements; | rain-making was among the feats essayed by primitive magicians, whose usual practice was to mutter incantations from mountain-tops; at a later stage explosives were often employed with the object of “shattering the clouds,” and, finally, the resources of modern chemistry and aviation have been called into play. It is. only within quite recent years that the basic physical facts of rainfall formation have become well understood. Meteorologists are now agreed that thermo-dynamical cooling, brought about by the vertical movements of air masses, can alone produce the necessary condensation of water vapour. Nature operates to this end through the medium of a vast and extremely complex heat engine, . in which the circulating fluid is the at-

) mosphere, with its moisture drawn from the ocean, and the furnace is the sun. Her processes are conducted on so gigantic a scale that man’s mightiest efforts seem by comparison puny in the extreme. To bring down the trifling amount of one-hundredth of an inch of rain over an area of one hundred square miles, a body of air containing 650,000 tons of water vapour has to be raised from the earth's surface. The methods adopted by would-be rainmakers appear, in most instances, to ignore the fundamental cause of the precipitation of moisture from the atmosphere. Since the Great War. which, for all its unparalleled expenditure of explosives, is not known to have altered the course of nature’s phenomena one whit, efforts to turn clouds of water by sheer concussion have been almost abandoned. M. Angot, head of the French Meteorological Service, showed that in the most favourable circumstances possible it would need the detonation of 21,750 tons of melinite to produce a single millimetre of rain over a square mile. Instead, modern experiments are chiefly directed to the supplementing of nuclei available for the condensation of water vapour from air by the admixture of highly ionised gases, electrified sand, or certain chemicals. —Spraying of liquid air at the cloud level has also been tried, with a view to lowering the temperature there well under saturation point. There are meteorologists who believe that when clouds are nearly, but not quite, ready to condense their moisture into rain the process may be urged forward by the application of suitable chemical or electrical stimulus, and this is presumably the view held by the authorities at Honk-Kong Observatory. The apparent success that has occa-

sionally attended similar evperim elsewhere does not fall outside*?,!* range of coincidence, however and i England efforts to cause shower.” C® such means during the sreat dron.w of 1921 failed completely. No upheaval yet produced by hrm agency can be ranked in the aT*® category as nature’s convulsions. w-v®* we consider that even the great*® volcanic eruptions, such as those* 6 ** Asama. iu 1753, and of Krakatoa, J* a century later, had apparently'™ Bl more recognisable effect on rainf? 0 , than had the Great War. though th were audible several thousand m? away, and for months filled the whnl* world’s atmosphere with dust part? cles well suited to act as nucleif condensation, we are led to donh* whether man has ever, of his own v lition. called forth one drop of from the skies.