Epidemics. 27 



A more careful examination into the causes of epidemics 

 is now given than at the commencement of the Sketch, 

 from a reconsideration of the materials and data gone 

 over, in which much recapitulation may be observed, 

 yet for the end of viewing the same general facts from 

 different points, this form of analysing is the most fit 

 for a subject in itself naturally so difficult, and may be, 

 in some measure, examined from a more general survey of 

 leading facts ranging over a longer period of history than is 

 usual in such matters. 



Climate, heat, drought, mildew, locusts, heavy rains, 

 earthquakes, volcanoes, trade winds, &c., are here briefly 

 referred to ; and in their relation to vital force, or its 

 abstraction or perversion, as in the form of disease, these 

 several agencies are admitted to have a very marked effect, 

 but all of them more of an endemic, rather than of an 

 epidemic nature. But such diseases as the Levant plague, 

 or cholera, from their regular advance, and encircling 

 the whole globe, and continuance from time to time over a 

 long series of years, can scarcely be viewed as arising from 

 changes wrought by an eclipse, comet, earthquake or volcanic 

 eruption, or mildew, or locusts, etc., etc. 



A brief examination is instituted of the change in tempera- 

 ture on the earth's surface from the time of Job on to our 

 own time ; or from 1500 or more B.C. to 1870 ; showing 

 generally that heat has increased as we near the tropics and 

 decreased towards the Arctic regions in regular gradations 



