PROBLEAIS L\ TERRESTRIAL PEIYSICS THAT RE- 

 QUIRE THE ATTENTION OF SOUTH AFRICAN 

 PHYSICISTS. 



By Prof. ToHX Tonn .Morkisox. M.A., B.Sc, F.R.S.E., 



A.MJ.E.E. 



There are severril ])riil)lems of world-wide interest in terres- 

 trial phvsics for tlie inx-estig^ation of which Sotith Afriea is 

 specially well fitted hy lier ,o'e'"'STa])hical situation and climatic 

 conditions. In regard tn snnie of these it nia\' even be said that 

 no general .solution is likely without the co-o]ieration of scientific 

 men in South Africa. The organization, or at least the encour- 

 agement, of such researches seems a matter which lies jx-culiarly 

 within the province nf this Association, and I ha\e accordingly 

 \entured to call attention to one or two of them. 



I. The first ([uestion to which 1 should like to direct atten- 

 tion as speciallv suitable for research in South .\frica is the 

 determination of the intensit\- of solar radiation at the outer 

 limits of the earth's atmos])here, the so-called " solar constant." 

 This is probably the most important datum in meteorological 

 phvsics. Its accurate determination is an essential for any 

 reasoned discussion of the distrilnuion ui temperature. i)ressm-c 

 and movement in the atmosphere. It has a profound bearing on 

 solar and i)lanetary physics, as well as on the study of the gen- 

 eral conditions of life on the earth. 



It has been the subject of in\estigation by many i)hysicists 

 in Europe and America, notably 1))- Langley and his successors; 

 l)Ut its value is still the subject of dispute, owing chiefly to dif- 

 ferences in the e.stimates of the loss the radiant energy suffers 

 in its passage through the atmosphere. The ([itestion has recently 

 entered on a still more interesting phase, through the observa- 

 tions of Abbot, Fowle, and j'dudich,* the Mount Wilson ob- 

 servers, who believe that thev have shown the radiation itself to 

 fluctuate considerabK within the course even of a few weeks, 

 quite independently of the state of the earth's atmosphere. This 

 observation, if contirmed. would obviotisly l)e a discover}' of 

 great importance, alike in solar and in terrestrial ])hysic>. It 

 can hardly be satisfactorily either u])held or disproved, excejtt 

 by a succession of observations made simultaneously at stations 

 w'idely separated on the earth's suface. so that it may be deter- 

 mined whether the observed variations arise from local atmos- 

 pheric changes not duly allowed for, or are world-wide in 

 character. 



For observations of solar radiation, a first recpiisite is the 

 reduction of atmo.^pheric absorption and scattering to the lowest 

 l)OSsible point. For this purpose, the observing station (if there 

 is only one) should be high, its climate should be dry, and it 



* C. (i. AI)t)oi. I'hvsicai l\'i-viezi'. Vol. VI, Ser. 2, pp. 504. .^05. 



