188 ELEMENTS OF STATIC ELECTRICITY. 



the globe, we may reasonably infer that similar results 

 would be observed 011 every part of it; and hence, 

 that east and west currents are constantly traversing 

 the earth, as it revolves from west to east. 



This will be more fully understood, when we con- 

 sider, that, during the diurnal revolution of the earth, 

 the sun occupies practically a fixed position with ref- 

 erence to it : so that from the earth's heated hemi- 

 sphere, electric currents are constantly flowing, from a 

 central point where the sun's rays are vertical, in 

 opposite directions, towards a point within the cooler 

 hemisphere, opposite to the sun. 



But the diurnal revolution of the earth brings any 

 limited area of its surface, surrounding an observer, 

 alternately into each of these currents. So that, while 

 they have a fixed direction with reference to the sun, 

 and to the earth, as a whole; they become, alternately, 

 east or west currents, with reference to such an area. 



From noon to midnight this area would be in the 

 west to east current ; and, from midnight to noon, in 

 the east to west current; an equatorial point, on the 

 observer's meridian, passing the point from which the 

 currents diverge, at noon ; and reaching the point 

 towards which they converge, at midnight. 



At both these hours, the temperature, at equally 

 distant points in the observer's latitude, reaching from 

 his position, east and west to the sensible horizon, is 

 nearly the same : and the noon and midnight minima 

 of electric potential are the result. 



At sunset and sunrise the temperature on similar 

 quadrants of the observer's latitude, east and west of his 

 position, attains its maximum difference ; and the even- 

 ing and morning maxima of electric potential occur. 



