and Departures in the United States. V2i6 



sun-spot numbers. It must be fully admitted that meteorolo- 

 gists have an exceedingly complex problem before them, but 

 in view of the valuable results to be derived from a correct 

 forecast of seasonal weather conditions, they will be justified 

 in pursuing these studies to a practical conclusion. 



Obseroations on the Solar Radiation and their Interpretation, 



It will be seen from the foregoing statement of the several 

 lines of correlated phenomena that the continuous record of 

 the solar radiation is the missing link in the chain. The 

 prominences and the sun-spots are products of the outgoing- 

 radiant enei'gy and the accompanying solar circulation ; the 

 magnetic field variations are one result of the absorption of the 

 incoming radiation in the earth's atmosphere, and the temper- 

 ature changes are another product of it, linked up with the cir- 

 culation, and thence with the barometric pressure and weather 

 conditions generally. The study of the entire series of observa- 

 tional problems is greatly hindered at every turn by the instru- 

 mental expense of securing the necessary original observations, 

 and the complicated results to be interpreted. It constitutes 

 the greatest world problem for future generations to more 

 pei'fectly work up and utilize. At present the magnetic field, 

 all things considered, is the most suitable for the practical 

 foundation. We have numerous magnetic observatories in all 

 parts of the world, and the observations are easily secured. The 

 magnetic vai'iations are direct products of the incoming radia- 

 tion through the process of ionization and electric currents, but 

 there is a regional assorting going on in the earth's atmos- 

 phere, part of the incoming energy being transfoi-med in the 

 outer, thin, dry layers, and another part in the lower, dense, 

 moist layers of the earth's atmosphere. Certain corpuscles 

 and cathode rays may have special, irregular operations in the 

 outer layers to produce spasmodic magnetic storms, but it is 

 the transformation of energy in the lower layers that are 

 chiefly concerned with the diurnal and the annual periodic 

 variations of the magnetic field. We have only to interpret 

 these in terms of solar radiation and terrestrial circulation to 

 connect up the two branches of this subject. 



The direct observations on the incoming solar radiation, by 

 means of the bolometer i-eadings on the individual rays of the 

 spectrum, and the pyrheliometer on the total or integrated heat 

 energy, are beset with unusual difficulties, partly instrumental 

 and partly meteorological. The splendid progress made by the 

 Smithsonian Astrophysical Observatory in developing a relia- 

 ble instrumental equipment makes us hopeful of a practical 

 result in respect to the observations. The meteorological 

 problem, depending upon the temporary constituents of the 



