48 New Theories of the Great Forces. 



This line of magnetic, or heat activity, 

 consequently varies with the earth's move- 

 ments. On the 20th of June the flood of 



SEASONS. SUMMER. 



PI. II. 



summer heat overspreads the northern por- 

 tions of the earth ; the sun thence apparently 

 turns southward, and with its departure the 

 relations of the line of heat activity change. 

 The city of New York, which on the 2oth of 

 June is found nearest the centre of the solar 

 current (Plate II. b), is, on the 2ist of De- 

 cember, located at its greatest distance from 

 the line of magnetic or heat intensity 



