148 Epidemics. 



Our trade winds, siroccos, monsoons, etc., take their lead- 

 ing course of current, or direction of motion, from the com- 

 bined action of rarefaction from the sun's heat, and the angle 

 in relation to the earth's orbit at which the sun's rays fall 

 upon any particular portion of the earth's surface ; but if the 

 appearance in time of such periodic wind currents depended 

 solely upon the sun's rays, then they would always appear 

 to the day and the minute in every part of the earth's sur- 

 face where they are found; for the time the earth reaches any 

 particular part of its orbit, and the amount of light which 

 shines upon any particular part of the globe being always 

 the same, the time of their appearance would be always 

 identically the same, year by year, from age to age. But 

 inasmuch as occasionally they are a few days too early, and 

 frequently a week or two weeks later than their accustomed 

 time, it is plain that some agency beyond that of the sun's 

 rays has a powerful effect, and is a disturbing element in 

 this perfect system of light administration, whereby the 

 legitimate effects of solar calorification are limited, and 

 diverted from their correct time of systematic recurrence. 



The general inference, then, is this that in relation to 

 epidemics the sun may be viewed as an indeterminate 

 agent, and a non-producer of epidemics. The one sole 

 agency of the sun, external to his direct rays, as chemical, 

 actine, calorific, and luminous, if such divisions of the rays 

 are tenable in the present day, in the latter of which the 

 solar spectrum apparently reveals identical elements in the 

 sun to those that exist upon and constitute the chief 

 elements of the earth, which in many respects, to say the 

 least, is exceedingly problematic to repeat, the sole agency 

 beyond the rays of the sun are the spots of the sun. 



Whatever may be the exact chemical constitution of the 

 matter of which these spots are composed, two facts are 

 apparently clear ; first, that the spots are non-luminous ; 



