SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE. 



OBSERVATIONS 



TERRESTRIAL MAGNETISM 



MEXICO. 



CONDUCTED UNDER THE DIRECTION OF 



BARON VON MULLER, 



WITH NOTES AND ILLUSTRATIONS OF AN EXAMINATION OF THE VOLCANO POPOCATEPETL 



AND ITS VICINITY. 



BY 



AUGUST SONNTAG. 



[ACCEPTED FOB PUBLICATION, MAT, 1859.] 



