SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE. 



OBSERVATIONS 



TERRESTRIAL MAGNETISM 



MEXICO. 



CONDUCTED UNDER THE DIRECTION Of 



BARON VON MiJLLER, 



AYITH NOTES AND ILLUSTRATIONS OF AN EXAMINATION OF THE VOLCANO POPOCATEPETL 



AND ITS VICINITY. 



BY 



AUGUST SONNTAG. 



[ACCEPTED FOR PUBLICATION, MAT, 1859.] 



