THE SUN AND THE ATMOSPHERE — STETSON 165 



the charged particles would vary very materially from a straight line 

 as they are distorted, both by any magnetic field which the sun may 

 possess and by the magnetic field of the earth when the corpuscles or 

 electrons arrive in the neighborhood of our planet. We should, 

 therefore, preserve an open mind relative to any corpuscular theory, 

 for negative evidence is never completely convincing. 



It seems hardly necessary to emphasize the desirability of contin- 

 uing measurements of radiation from the sun such as have been con- 

 tinued for so many years by the Smithsonian Institution. In con- 

 nection with measuring the total amount of the sun's radiation it 

 appears especially important that systematic measurements of the 

 ultraviolet in sunshine should form an important part in gaining 

 information as to the interrelation of the sun and the earth. Daily 

 measurements of the strength of the ultraviolet in sunshine made by 

 Pettit at the Mount Wilson Observatory over many years appear to 

 indicate that in general ultraviolet radiation is more intense near 

 sunspot maxima than at sunspot minima. There are, however, 

 many disconcerting discrepancies. A remarkable drop in the ultra- 

 violet radiation from the sun, for example, occurred in the early part 

 of 1936 while solar activity was still rising. It must be remarked 

 that ultraviolet is probably the source of the creation of ozone in the 

 upper air, and at the same time any increase in the ozone content 

 naturally screens from the earth's surface the greater part of this ultra- 

 violet radiation which produces it. Since ozone, therefore, absorbs 

 the greater part of the sun's ultraviolet radiation, it would appear 

 that with any sudden increase in the ultraviolet there would be a 

 concomitant increase in the amount of ozone which, in turn, would 

 effectively reduce the quantity of the ultraviolet light which we would 

 measure at the earth's surface. This seriously complicates the prob- 

 lem, and may account for the fact that a smaller value of the ultra- 

 violet radiation would actually be recorded by our instruments even 

 though its emission from the sun at the same time might be enhanced. 

 Similarly, a sudden dissociation of ozone due to a decrease in the 

 amount of ultraviolet emitted from the sun might well result in a 

 sufficient thinning of the ozone layer to allow apparently a material 

 increase in the amount of ultraviolet coming through the atmosphere 

 to the earth. Our instruments, therefore, would indicate more ultra- 

 violet at a time when the sun might actually be emitting less. 



When we take averages of ultraviolet radiation over the years and 

 compare them with solar activity, the correspondence between sun- 

 spots and ultraviolet radiation is much more striking than any day- 

 to-day or week-to-week correspondence can exhibit. It would appear 

 feasible and highly desirable that observations of ultraviolet should 

 be made from the stratosphere, utilizing balloons for carrying the 

 recorders aloft. We find that the Smithsonian Institution already 



