FORECASTING WEATHER. ONE MONTH IN ADVANCE Series of Interesting Experiments

Progress, Volume II, Issue 6, 1 April 1907, Page 221

FORECASTING WEATHER. ONE MONTH IN ADVANCE Series of Interesting Experiments

Scientific men of the Smithsonian Observatoiy at Washing ton, having the co-opeiation of the United States Government, have undertaken a senes of experiments of moment to science m general Should their efforts be as productive of lesults as they sanguinely hope, it will soon be possible to forecast climatic conditions over large areas with reasonable accuracy for weeks They ate attempting to demonstrate, if possible, beyond scientific peradventure, that variation in heat radiation from the sun has directly to do with meteoiologic conditions on the earth Success will mean that the whole system of weather forecasting will be revolutionised The benefits of such a system if measurably accurate, would be inestimable to the agiicultural nterests of the country Husbandmen could be safel} guided largely in their planting and care of crops by the indications it is proposed to issue under the official supervision of the Washington Government The experiments are being made at the great

observatory on Mount Wilson, in Southern California. Equipped with instruments of marvellously delicate construction, daily obseivations aie being made 6,000 ft. above the sea level One of these instruments is the wonderful electric thermometei, known as the bolometer, which legisters variations of fhe sun's radiation in milhonths of degrees Outside the sheltered tent m which the instrument is installed is kept in the sunshine an instrument which, by means of mirrors, will thiow a constant beam of sunlight into the adjoining dark room wheie it will pass through a prism, and from one reflector to another into the bolometei This instrument registers changes in radation by a magnetic needle which swings like that of a compass, with a beam of light as a pointer, reflected from a mirror fastened to the magnetic needb The mirror, which moves every time there is the shghtebt variation in radiation, is of pmhead size, but it reflects a tiny beam of light upon a long moving photographic plate, and the photograph upon the plate is a zig-zag line, which goes to and fro as the bolometer is warmed or cooled by changing sun rays The expedition which is making the observations on Mount Wilson is under the supervision of Mr. C. G Abbott, director of the Smithsonian Observatory at Washington, accompanied and assisted by an expert fiom the National Department of Agriculture Mr Abbott outlined in

an interview in the " Daily Mail" what it is hoped to accomplish by these experiments and upon what scientific gioundb, as follows — " Although the sun has shone upon this earth for some thousands ot \ears since men were present to see the matter still : emams open for us to deteimine whether the amount ot radiation the sun sends oui way remains sensibly constant or fluctuates sufficiently to affect climate considerably , and this is the que.tion which the Smithsonian Observatoiy is seel rig to solve Of couise if we conhne oni attention to any place on the earth's surface, we are well aware that there are several causes which affect the mteivity of sunshine Fust, there is the change of distance ol the earth from the sun, which causes the intensity to be about b per cent greater in January thin in Jul\ Second there is th" inclination of the earth's axis to the ■ line of its orbit around the sun, which ciuses the rays to fall more obliquely in winter than i.i summei, so that although their mtensitv as measured on the surface at right angles to the beam n, as just said, greatest in January, yet January is cbarer than July in the northern hemisphere Third, theie is the rotation of the earth on its a^is, which produces changes of temperature between day and night All these and some other causes produce penodic changes of temperatuie whose amounts would be easily piedicted perhaps, if the earth had no water or air upo lit But the air

is loaded moie 01 less with dust, watet vapour, clouds and carbonic acid vapour, all of which exercise profound influences on climate and weather which change fiom day to day and day to night, and from season to season Of these irregularly variable elements, which must be reckoned with in the study of climates, watei in its several forms is by far the most impoitant I will speak of only a few aspects of its influence The oceans are heated by the sun dnectly so much deeper than the land and the wate s of the surface mix so freely with those of the lower layeis owing to currents, winds, and waves, that the changes of sunshine from day to night and from winter to summer cause only a comparatively bmall change of ocean temperatures Therefore land which joins the ocean is moie constant in tern perature than inland regions But water is also evaporated from the oceans, and in this process heat is taken up with the vapour into the air. So long as the watei vapour remains invisible in the air the heat lemains in it, but as soon as a fog or cloud is formed this heat is again freed and this is one of the reasons why frosts are less feared in cloudy weather While water vapour is still invisible, however, it controls the earth's temperature in a marked degree, for, though so transparent as to be unnoticed, watei vapour is as opaque almost as steel to many of the rays which a body of the temperature of the eaith ib sending out. Many peisons do not leahse

that there are rays which we would call light if our eyes could only see them, but which are of longer wave length than we can see, just as some sounds are too low in pitch to hear. It takes a very hot body, like the sun, to send out white light, a cooler body sends out red light, and a still cooler one, like the earth sends out invisible rays. We now see why the water vapour would keep the earth warm, for it lets the sun's rays in almost unchecked, and holds back the earth rays from passing out into space In the form of clouds the water behaves differently, for clouds are very good reflectors of sunshine, so that if the earth wee wholly covered with clouds, neaily three-quarters of the sunlight would be reflected away from us We now see how difficult it is to know the effect of a greater or lass intensity of sunlight on temperature For more sunshine means more evaporation, and who can say whether an increase of water vapour will increase the cloudiness m any particular locality, or, if it does, whether the increase of cloudiness will reflect away more sunshine than the increase of the sun's intensity naturally introduces ? However, taking the world as a whole, it seems a very reasonable thing to suppose that if the sunshine grew stronger the temperature would generally increase. Accordingly, the first step towards forecasting of climate will be taken if we find that the radiation of the sun varies considerably in amount.

The sun is so enormous in size that the earth, and the moon 1 evolving about the earth in its orbit of 240,000 miles radius, could be entirely hidden from View within the sun . and, as the great bodies change slowly, it is to be expected that, if conditions on the sun should lead to a greater output of its radiation this month, the output would hardly fall to its ordinary level before the end of next month. Thus, it will be pretty safe to predict that the effects of each change of the sun on the climate of the earth will last for several weeks at least."