.NO. II ATMOSPHERIC OZONE FOWLE 21 



With the assumption of these two sources for the origin of the 

 atmospheric ozone, several of the phenomena shown by the observa- 

 tions of this paper fall in line, and our fifth conclusion will be : 



(5) (a) Due to the ultra-violet light from the sun, there is a layer 

 of ozone, varying apparently very little with the sun-spot 

 period, and situated over both the northern and southern 

 hemispheres and showing an annual march having its maxi- 

 mum in the spring of both hemispheres and its corresponding 

 minimum in the autumn. 

 (b) There is another layer formed under the bombardment of 

 electrical particles (probably positive ions) emitted from the 

 sun and showing strongly a dependence u|X)n solar activity as 

 indicated bv Wolfer's svm-spot numbers. At the only minimum 

 of spots observed this layer appeared practically absent, the 

 measurements indicating the presence of the (a) layer alone. 



Though the corresponding marches during the year of the ozone 

 (which the writer proposes to attribute to the first of the above 

 causes) occur in diflferent months in the two hemispheres, the seasons 

 of maximum and minimum are the same, namely, spring and autumn. 

 One might be led to suppose that these variations are due to some 

 dependence upon the annual and reciprocal marches in the two 

 hemispheres of the air-masses through which the sun's rays could 

 jienetrate for the formation of ozone. Further at the tropical station 

 at Montezuma the sun is more nearly overhead and the air-mass 

 change smaller, which might perhaps account for the smaller annual 

 range there. However the maxima and minima do not occur at times 

 when the sun is farthest from or nearest to the zenith, when there 

 would be the greatest and least air-masses. 



Another circumstance might lead to an explanation of the annual 

 )narch and its reciprocal effect in the two hemispheres so far as 

 concerns the times of occurrence of the maxima and minima. An- 

 nually, as viewed from the earth, the sun's equator reaches its greatest 

 southern displacement (7.25°) about March 7, and its greatest 

 northern displacement about September 8. The aspect of the sun's 

 disk as seen from the earth at these epochs is shown in figure 12. 

 Since the earth subtends only about 30', as seen from the sun, under 

 either circumstance, the sun would have practically the same" aspect 

 as viewed by ultra-violet light from either the northern or southern 

 hemispheres of the earth. However, the ultra-violet light would 

 probably be strongly scattered by the particles of the solar corona, 

 and this annual shift of the far more extensive and considerably 



