METEOROLOGICAL

Hokitika Guardian, 17 July 1925, Page 4

METEOROLOGICAL

Ti; F. DICTIONS AYE Fix AHEAD.

[nv Tur.EGitArii —rt;it pjikss association.] NEW YORK, July 12. The temperatures have been predicted almost ;t week in advance with approximate accuracy daily for a year by the determination of the solar radiation, according to a statement issued from the Smithsonian Institute. One of the most important additions to our knowledge made during the iiast twenty years lias been the exact determination of the amount of heat radiated from the sun: ibis Inis been ascertained by measuring the heat received per second at the earth’s surface. When the work was l>ogmi there was no idea that the amount- of heat so received varied; it was believed to lie a constant quantity, and was therefore termed the solar constant, aml this name has been kepi though biter investigations showed that the stm s radiation did not always have the same intensity. Without going into details we may say that the mean value was found to hv‘ I Jll. i.e. the amount nl radiant heat from the sun tailing l<erpemlieuliiiiy on a square eontrimetre, if the earth's atmosphere were removed. was sufficient m raise the temperature of a grain of water in one second by 1 .92 degrees Centigrade. The foremost worker in this field Inis been Dr C. O. Abbott, of the Smithsonian T.i.jj-ititto. and the observations have l>ecn mainly carried on at stations at Mount Harquii Mala, in Arizona, and Mount Montezuma, in Chile, with a check station in Algeria. Ibe principal diffieutly encountered has liven in making the proper allowance for the amount of beat absorbed by the earlh s atmosphere before it has reached the recording instruments, but the skill and patience of Dr Abbott and bis coworkers have overcome this, and row the observations at the dillercnl stations show stteli a high degree of concordance that the results obtained may lie received with confidence. l)i- Abbott has just, published in a oraphieal form Die results ol Die o >- serrations taken at the mountain station from IHIS to 1921. and Horn jus Graphs eerl ain conclusions ol some interest may be gahered. In the litst ljm-e, Die solar radiation is subject to rapid’ variations, so that within a comparatively short space of time usjnea-sui-e has changed from LIU to Lib, lUI alteration of about two per cent, in its value, a variation which cannot have occurred without aflectuig eoiisidct abL Die meteorological conditions prevailing on the earth’s surface. Again, we note that the average value of Die solar radiation is much higher during tin* vo-ir.s when sun-spots have lie'll prevalent on the sun’s disc. Dun. during llir VCMTS when till' SUJTjUO ll!iS II relalitelv quiesce 111. The yars MRS|!IPI marked tie- .lose of a sun-spot period. when iinieli aetivil.V was limilliVsteil in the solar atmosphere, anil during lbest* years we enjoyed relatively hot stllillliers and mild winters; in 19_X the average value of the solar constant fell, reaching neeirdnig lo T' graph - a reading of only I ,SS m Dm September of Diat year, and since Dint date. Din,tell it has llm l ual ed consideral.lv. il has never readied Die moan value oi' I .ID. These lain' years have been characterised by a lower average temperature on tbe earth’s surl.-iec and more humid conditions generally, i The material accumulated is now being studied with tbe object ol dete;iiiiiiing tbe relation l. 'l ween change!in Die amount of tbe solar radiation, and climatic variations, and we may hopefully expert Dial some important eoiirl usiolis will result I rom this study, some I into [nisi the meteorologist! of the Argentine have been supplied with informal ion with a lair lueasnu of success to lb" difficult problem ol : ivp'itier I'oreeastiii'i. As all our mej toorologieal activities are d-pendeut oi the sun’s beat, it is only reason.d.b . lo ex I et that as our knowledge <> ' ' s .,!ar eonditioiis iner* we 'ball he 1 t -,1.1,1 to trier with pieaier surety tbeo ' i ~ii',.,.t s on terrestrial climate, and Dim . ‘ prepare the way lor far more elm vie i’ll forecasts of weather than we now

i ... . i , \t a meeting m .xovemhep ' the Royal Astronomical Sm-iety. M • learn-. F.li.S. sPl'eni ,-f ibf smioty- put forward at t'xreniclv interesting app’h''>Dm' of mu knowledge of the solar constant. Ha ■ •euerallv held now. Dial the energy expended by our sun and ot lier star: in the lurm ol radianl heat i- mam t.aiia-il 1 1 \ the conversion of mailer ill in energy, though the exact nature o the mechanism by which Ini" ciinngc i ell'-'t'led i-- not uuder.-loc.rl. From tb< known value of the s Jar constant, lb

Jeans lias calculated that the sun nuts be losing mass at the rate of no lesi than .1.209.1 JO tons a second, while tin | mass of a giant, star of absolute mag j nitmle - A must be decreasing a 111. (11)11 t i 111 •■ - ibis rate!

j Sucli a loss 111 mass each sec mil as i over four million tons .-trikes us as I stupendous, but we must view it in re- ; lalion to tbe sun's mass, wbieh is enorj mutts compared with that ol tbe earth. i |t will help us perhaps to visualise ! what is taking place when we find that a cube of silver wlio.-e edge is 81. yards long, would weigh almost exactly J.2J!'l.!'-I)'t tons and that the mass lost by the sun (luring a whole year would only weigh as mtlcn as a plate of silver, one im-h thick covering the entire surface of the earth. It would take 122 million years for the solar mass to diminish by an amount equal to the earth's mass.

It is, however, necessary to bear in mind Dial Die rate at which a star loses mass by- conversion of its mailer into radiant energy depends on Dio mass of tile star, the rate ol loss being faster when the mass is large than when it is small. If the solar mass is being lessened. it must have liven greater in Die past than il is now; there may have been a time when the sun’s mass was double its present value and there is even Die possibility- that il once had lour limes as much mass as it now lias. If this ever happened our .sun would lie a B-type siar-tit its maximum brilliant anil surface tem-perature—-and Dr Jeans shows that it our sun in its evolutions ever passed through this stage, il did so about 7.1 million million years ago.

This continuous loss ol mass which our sun is undergoing litis another interesting aspect. The earth amt other planets of the solar system are held in their orbits by Dio sun’s attraction, and the force with which Die sun attracts a. planet depends on the solar mass; if DiP.l tile .sun’s mass is slowly deereasing. the attractive lone it exerts on the planets is also slowly decreasing ami their orbits are therelore being slowly enlarged. Looking backthen we see that there must have been a lime in Die distant, pass when the pin net - circled round the >un in closer attendance than now. Me cannot, however, learn anything very definite about the primitive orbits oi the diflcri'Ut planets as we do not know bow long they have been in existence as separate eiu ii i s. There seems good rca-on to believe Dial some of the oldest known rocks on Ibe earth snrl'ac e are over lotto million years old. and even il Die material composing the earth bad been collected together for a similar period of time before it bad cooled down sufficiently for its rocks to crystallise, 2000 million years i.-, too short an interval in Die suit's evolution tor any' very marked change in the orbits ol the planets to have takeiKplaee. AA’iien he conies to deal with tne stellar universe as a whole. Dr Jeans writes; “The mass of the galactic system, of which our stm is a memlier. must be decreasing with a time-scale which is comparable with that ol a typical star. If. as Poincare .suggested. the Milky AA'ny may be regarded as an encircling belt of stars held in equilibrium by slow rotation, then the radius of this ring must be continually expanding. . . If, as is more natural, we regard the galaxy as a system <>t independently moving "tars. . . .tne galaxy must lie slowly expanding. AA'lien our sun was a B-type star, and so of mass equal to four times it" present mass, the mass of the whole galaxy must have Keen at least four times w licit it now is. At this time the radius of the galaxy would he less than a quarter of its present radius and the stars [irn-ked together at least sixty-tour times as closely a" they are now." Me leave ibis enthralling''aspect of stellar evolution with the thought that tf there were any astronomers observing the heavens 7.1 million million years ago, they must have had a glorious time.