Epidemics. 291 



amount of the sun's rays falling on our planet from year to 

 year during the whole of this period. 



Under similar solar conditions our monsoons, siroccos, 

 and trade winds, which, according to the solar theory, ought 

 to come to the minute year by year, are far from obeying 

 that law of uniformity ; for so great is their deviation from 

 this rule, that year by year the agriculturists and the tax- 

 gatherers in India are looking for their advent with the 

 greatest anxiety, as their frequent delays so materially 

 affect the crops, which for want of sufficient rain within a 

 given time determines their almost total failure, or contrari- 

 wise, an abundant harvest. 



If it is not the sun's rays, nor yet the qualified intensity of 

 them, through the spots or opaque masses on the sun's disc 

 which are observable from time to time, what is the 

 efficient cause of so much . variation of temperature on the 

 earth's surface, within given areas, which is capable of pro- 

 ducing such an amount of irregularity ? It will be said that 

 the ever-varying conditions on the earth's surface, from the 

 slow and gradual changes of depression and elevation in the 

 masses resting on the surface, are the efficient causes. 



But this will suffice. For, putting on one side the general 

 and vague statements of older writers B.C., let us consider 

 one or two of the remarks of authors since the time mercury 

 was received as a standard of measure for temperature. 

 Fahrenheit's being used in this country as the usual standard, 

 it is here followed. Quoting from Haydn 



In 1796, Dec. 25, London, cold 16 below zero. 



,, 1854, J an - 3> c ld 4 below zero. 



,, 1860, Dec. 25, ,, cold 18 to 15 below zero 



in several places in 

 England. 



,, 1810, Jan. 13, Moscow, mercury frozen hard. 

 Here four instances are given, and many might be added as 



192 



