knowledge of various kinds, have led me to occupy myself for many years --
and apparently exclusively -- with separate branches of science, as, for
instance, with descriptive botany, geognosy, chemistry, astronomical
determinations of position, and terrestrial magnetism, in order that I might
the better prepare myself for the extensive travels in which I was desirous
of engaging, the actual object of my studies has nevertheless been of a
higher character. The principal impulse by which I was directed was the
earnest endeavor to comprehend the phenomena of physical objects in their
general connection, and to represent nature as one great whole, moved and
animated by internal forces. My intercourse with highly-gifted men early
led me to discover that, without an earnest striving to attain to a
knowledge of special branches of study, all attempts to give a grand and
general view of the universe would be nothing more than a vain illusion.
These special departments in the great domain of natural
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science are, moreover, capable of being reciprocally fructified by means of
the appropriative forces by which they are endowed. Descriptive botany, no
longer confined to the narrow circle of the determination of genera and
species, leads the observer who traverses distant lands and lofty mountains
to the study of the geographical distribution of plants of the earth's
surface, according to distance from the equator and vertical elevation above
the sea. It is further necessary to investigate the laws which regulate the
differences of temperature and climate, and the meteorological processes of
the atmosphere, before we can hope to explain the involved causes of
vegetable distribution; and it is thus that the observer who earnestly
pursues the path of knowledge is led from one class of phenomena to another,
by means of the mutual dependence and connection existing between them.

I have enjoyed an advantage which few scientific travelers have shared to an
equal extent, viz., that of having seen not only littoral districts, such as