Alexander von Humboldt : a metabiography

Rupke, Nicolaas A.
Chicago : University of Chicago Press, 2008.
University of Chicago Press pbk. ed.

The Copenhagen papers : an intrigue

Frayn, Michael.
New York : Metropolitan Books, 2001.
1st American ed.

Helmholtz : from enlightenment to neuroscience

Meulders, Michel.
Cambridge, Mass. : MIT Press, [2010]

Hermann von Helmholtz and the foundations of nineteenth-century science

Berkeley : University of California Press, [1993]

The Humboldt current : nineteenth-century exploration and the roots of American environmentalism

Sachs, Aaron (Aaron Jacob)
New York : Viking, 2006.