NATURAL CYCLES

Otago Witness, Issue 4042, 1 September 1931, Page 10

NATURAL CYCLES

THEIR IMPORTANCE STRESSED LECTURE BY DR FOCKEN. Cr C. M. Focken, lecturer on physics at the Otago University, gave an illustrated address at the meeting of the astronomical branch of the Otago Institute on Tuesday evening, taking as hie subject “ The Importance of Natural Cycles.” The lecturer said that there were some problems to-day which were unlikely to yield a solution to attacks along one particular direction, but which were more hopefully attacked on many fronts by the concerted action of numerous specialists in different branches of knowledge. One such problem was the origin and cure of cancer, another the structure of the atom, and a third, he hoped to show, was the problem of natural cycles. This study of cycles, besides interesting many scientists, threw light on fundamental human problems. The term cycle was used in different senses in astronomy and in physics, and was even used loosely for any long interval of time. However, in physics, and he thought .he might add in general scientific use, the word denoted recurrence of different phases which were often susceptible to exact measurement, but had no necessary relation to a definite time interval. Even the sunspot cycle, with which they associated a fairly definite time interval, had varied in length from seven to seventeen years since 1788, when it was first observed. The lecturer said that the enormous advantage derived from a thorough understanding of cycles was that of prediction in a broad sense of the terms. Tn astronomy the prediction of eclipses, occullations, transits of Mercury and of Venus across the sun’s disc, date of return of comets and such periodicities could be made with an accuracy which even in these enlightened times impressed the uninitiated as almost superhuman. In the case of weather prediction an accuracy of 60 to 70 per cent, was possible only with fairly definite events which were to take place within a limited interval of time—usually 24 hours. If, hov’ever, the apparent connection between major sunspot maximum 'and drought were confirmed, it would be possible to anticipate a drought with some definiteness to the year by means of the annual progression of sunspot numbers. The layers of trunks of trees presented several features which were largely determined by the radiation, temperature, rainfall and ground-water supply accompanying their formation. Consequently large old trees and fossil trunks were potentially a most valuable record of the course of climatic variations. The lecturer

stated what had been done to secure in* formation by the use of the dendrograph, an instrument which made a continuous record of the variations of the diameter' of a tree between two contact points on opposite sides of the trunk, and he showed on the screen the character of the records obtained. The dendograph, it was pointed out, was useful in other ways in record-' ing the growth of trees, such as the daily and continuous variation due to changing tensions of sap and of hydration of living cells.

The question of tree rings was dealt with by the lecturer, who said that the.. longest records in annual rings obtained by Dr Douglass, of California, were secured from four 3000-year trunks in Californian redwood and referred to the deductions drawn from a study of the rings.

The lecturer said that development o£ general knowledge of climatic cycles would come by comprehensive investigation along at least three lines—the use of meteorogical data, tree growth studies, and clay layers or glacial varves. The greatest difficulty in utilising meteorological data was the inadequacy of the short historical records. In tree growth studies they had 3000 years of actual annual records gathered from extensive regions of the world. Clay layers showing most remarkable sequences reached over 3000 years in America, Norway, and Switzerland, and even in Sweden, Glaciers and ice sheets were conditioned by two opposite factors—nourishment and depletion. At times the ice front receded at an average rate of hundreds of feet a year; at times it was stationary or even in forward motion. The halts and readvances were usually marked by moraines, but the more detailed record could be expounded from the seasonally stratified varved glacial clays. The primary cycles of insects and animals were related to the season of the year, as was exhibited in growth, reproduction, etc. Cycles of Jiealth were often as clearly defined as other types of cycle, and an understanding of their underlying causes had great practical significance in the field of preventive medicine. Besson, who had made a careful analysis of th© death rate in Paris, declared that the death rates from pneumonia and infantile diarrhoea were so clearly a function of the weather that the rates for any special week eould be calculated within a few per cent., provided the rate for the year and the condition of the weather for two or three weeks were known. Further examples were given of the relation of weather to epidemics. The lecturer showed by a chart that there was a remarkably regular periodicity of seven years in the outbreaks of diphtheria and that the meningitis chart shewed an approximate 10 year epidemic spacing. The lecturer went on to speak of economic cycles, and said that in the quest for regularities it was allowable to entertain the hypothesis that both natural and social causes were at work. Meteorologists generally recognised that, as the sun’s radiation heats the earth’s surface, provided the energy of winds and evaporated water which fell as rain, so most of the variations from year to year in temperature, wind, and rainfall must he in some way caused by variations in solar radiation. The literature on the subject, which was immense, was mostly directed towards discovering direct and simple relationships between solar radiation, especially as represented by Wolf’s sunspot numbers, on the one hand, and terrestrial weather on the other hand. With a few isolated exceptions, however, > these efforts had met with little Ever since Galileo first observed sunspot ' blemishes on the sun, astronomers had considered that they contained the clue to many mysteries which could be traced to the sun, so they had been, and were still being, studied in great detail. The influence of the sun on the earth's climate, said the lecturer, was affected by four factors —water vapour ozone, carbon dioxide and dust. He referred to different aspects of the effect of these factors, and then dealt with the solar effects on the earth’s magnetism. There was a remarkable parallelism between the frequency of sunspots and the magnitude of the diurnal variation in the earth’s magnetic field. The two followed a similar 11-year cycle. Further, the best evidence established the tendering of magnetic storms to recur at intervals of 27 days, which was the period of the sun's rotation on its axis. In conclusion the lecturer said that they might agree with him that the surprising thing was not that natural cycles were imperfect, but that in the great interlocking complex they called Nature any cycles could be recognised at all. A hearty vote of thanks was accorded Dr Focken for his lecture.