with a roar of noise and a glory of daylight

Thoreau continued to search for this balance. Over the years, the struggle became less intense, but he remained worried. One evening, for example, when he had spent a day at a river, scribbling page after page of notes on botany and wildlife, he finished the entry with the sentence: ‘Every poet has trembled on the verge of science.’ But as he plunged into Humboldt’s writing, Thoreau slowly lost his fear. Cosmos taught him that the collection of individual observations created a portrait of nature as a whole, in which each detail was like a thread in the tapestry of the natural world. Just as Humboldt had found harmony in diversity, so too did Thoreau. Detail led to the unified whole or, as Thoreau put it, ‘a true account of the actual is the rarest poetry.’ The most graphic proof of this change came when Thoreau stopped using one journal for ‘poetry’ and another for ‘facts’. He no longer knew which was which. It had all become one and the same, because ‘the most interesting & beautiful facts are so much the more poetry,’ as Thoreau said.

What kind of science was this, Thoreau asked, ‘which enriches the understanding, but robs the imagination’? This was what Humboldt had written about in Cosmos. Nature, Humboldt explained, had to be described with scientific accuracy but without being ‘deprived thereby of the vivifying breath of imagination’. Knowledge did not ‘chill the feelings’ because the senses and the intellect were connected. More than any other, Thoreau followed Humboldt’s belief in the ‘deeply-seated bond’ that united knowledge and poetry. Humboldt allowed Thoreau to weave together science and imagination, the particular and the whole, the factual with the wonderful.

At a time when imagination had been firmly excluded from the sciences, Humboldt insisted that nature couldn’t be understood in any other way. One look at the heavens, Humboldt said, was all it took: the brilliant stars ‘delight the senses and inspire the mind’, yet at the same time they move along a path of mathematical precision.

In the history of publishing, the book’s popularity was ‘epoch making’, Humboldt’s German publisher announced. He had never seen so many orders – not even when Goethe had published his masterpiece Faust. Students read Cosmos, as did scientists, artists and politicians. Prince von Metternich, the Austrian Chancellor of State, who had so disagreed with Humboldt about reforms and revolutions, now brushed politics aside and enthused that only Humboldt was capable of such great work. Poets admired it, as did musicians, with the French Romantic composer Hector Berlioz declaring Humboldt a ‘dazzling’ writer. The book was so popular among musicians, Berlioz said, that he knew one who had ‘read, re-read, pondered and understood’ Cosmos during his breaks at opera performances when his colleagues played on. In England Queen Victoria’s husband, Prince Albert, requested a copy, while Darwin professed himself impatient for the English translation. Within weeks of the book’s publication in Germany and France, a pirated English language edition had begun to circulate – translated in such execrable prose that Humboldt worried it might ‘severely damage’ his reputation in Britain. His ‘poor Cosmos’ had been butchered and was unreadable in this version.

As Darwin read Personal Narrative, he highlighted many of these examples. Why was it, Humboldt had asked, that the birds in India were less colourful than those in South America, or why was the tiger only found in Asia? Why were the great crocodiles so plentiful in the Lower Orinoco but absent from the Upper Orinoco? Darwin was fascinated by these examples and often added his own comments in the margins of his copy of Personal Narrative: ‘like Patagonia’, ‘in Paraguay’, ‘like Guanaco’ or sometimes just an affirmative ‘yes’ or ‘!’.