Original sentence: Matthew Fontaine Maury subsequently revealed that Brazil had ordered the arrest of Alexander von Humboldt if Humboldt ever came there --  that great European scientist, Alexander von Humboldt, who had traveled elsewhere in South America
Edited sentence: Matthew Fontaine Maury subsequently revealed that Brazil had ordered the arrest of Alexander von Humboldt if Humboldt ever came there—that great European scientist, Alexander von Humboldt, who had traveled elsewhere in South America