28 Introduction. 



for 3300 years and more. That northern climates were 

 warmer and southern climates cooler in the early history of 

 the world, but during the progress of epidemic epochs they 

 have undergone a slow but sure change. 



Halley's theory of trade winds, &c., is generally admitted, 

 but denying the sun to be sole regulator of them, because, 

 if so, year by year they would return to the day and the 

 hour, which is far from being the case. 



An internal source of disturbance is suggested as a neces- 

 sary accessory to the sun ; to account for the checks to 

 winds and monsoons on the one hand, and for the varia- 

 tions of cold and heat on the other hand, occurring daily, 

 which, from being sudden, and not gradual, cannot have an 

 origin in solar distribution, or in the action of the sun's rays 

 on the earth's surface. 



A short examination of Gilbert's and Halley's theory of 

 -magnetism as being a revolving solid mass towards the 

 centre of the earth is given, and Dr. Barlow's and Haustein's 

 of more recent times, and the general conclusion adopted is, 

 that our chief disturbing agency to health, and promoter of 

 -disease has an internal rather than an external origin, viz. : 

 that of an electro-magnetic nature, or, that within the earth, 

 the electro-magnetic, or some like force, is disturbed, and 

 subject to consecutive changes which affect the surface of 

 the earth and its organized creation. 



The secular variation of the compass from east to west 

 is about 320 years, and back again another 320, so that a 



