CHAP, x.] VARIOUS APPLICATIONS OF ELECTRICITY. 725 



and the other phenomena of which the aerial covering of the globe 

 is the scene. 



We are already able to represent certain facts in a general way 

 and to mark the variations of some meteorological elements according 



FIG. 407. Secchi's meteorograph. 



to the localities, such as the annual isothermal lines and those of the 

 winter and summer seasons. The name isothermal is given to the 

 curve marking the localities where the mean temperature throughout 



