Measurements of the sun’s ultra-violet radiation and its absorption in the earth’s atmosphere

1. It is now well known that a connection exists between the variations in solar phenomena and changes in terrestrial weather. Thus the occurrence of an eleven-year cycle in the earth’s temperature, rainfall, etc., which is coincident with the eleven-year period of sunspots has long been recognised. More recently a marked connection has been found between the irregular short -period variations also. In this connection the work of H. H. Clayton, of the Argentine Meteorological Service, may be particularly mentioned. He has found that a very definite connection exists between the variations of the “solar constant,” as measured by the Smithsonian Astrophysical Department, and the temperature and rainfall some few days later in South America. The causes which lead to this connection are at present not known, though various theories have been proposed. For example, it has been suggested that the short wave-length radiation from the sun will produce ozone from oxygen in the upper atmosphere, and owing to the absorption bands of ozone both in the infra-red and ultra-violet, a change in the amount of this gas might change the radiation equilibrium temperature of the upper atmosphere, and so affect the pressure and temperature of the air below. The measurements of ultra-violet radiation made during “solar constant” determinations by the Smithsonian Institute are very uncertain, owing to the relatively small energy in this part of the solar spectrum, and the large errors due to stray light in the spectrometer. Since the measurements here described were started, Fabry and Buisson have published measurements of the amount of ozone in the atmosphere—measured spectroscopically—but only for about a dozen days.