Regardless of communication between man and man, speech is a necessary condition for the thinking of the individual in solitary seclusion. In appearance, however, language develops only socially, and man understands himself only once he has tested the intelligibility of his words by trial upon others.

Words well up freely from the breast, without necessity or intent, and there may well have been no wandering horde in any desert that did not already have its own songs. For man, as a species, is a singing creature, though the notes, in his case, are also coupled with thought.

[Herschel and Humboldt] stirred up in me a burning zeal to add even the most humble contribution to the noble structure of Natural Science. No one or a dozen other books influenced me nearly so much as these two. I copied out from Humboldt long passages about Teneriffe and read them aloud on one of [my walking excursions].

I find in Geology a never failing interest, as [it] has been remarked, it creates the same gran[d] ideas respecting this world, which Astronomy do[es] for the universe.—We have seen much fine scenery that of the Tropics in its glory & luxuriance, exceeds even the language of Humboldt to describe. A Persian writer could alone do justice to it, & if he succeeded he would in England, be called the 'grandfather of all liars'.— But I have seen nothing, which more completely astonished me, than the first sight of a Savage; It was a naked Fuegian his long hair blowing about, his face besmeared with paint. There is in their countenances, an expression, which I believe to those who have not seen it, must be inconceivably wild. Standing on a rock he uttered tones & made gesticulations than which, the cries of domestic animals are far more intelligible.