Excerpt from The Age of Wonder by Richard Holmes, plus links to reviews, author biography & more

The Endeavour expedition remained for three months on Tahiti. Its main object was to observe a Transit of Venus across the face of the sun. (Cook stated that this was the reason their settlement was named Fort Venus, though his junior officers gave a different explanation.) This was due on the morning of 3 June 1769, and there would be no other transit for the next hundred years (not until 1874). It was a unique chance to establish the solar parallax, and hence the distance of the sun from the earth. This calculation depended on observing the exact timing at which the silhouette of Venus first entered, and then exited from, the sun’s disc.

Banks was not part of the astronomical team, but when the expedition’s quadrant was stolen one night shortly before the transit was due, he reacted with characteristic energy and courage. He knew that without this large and exquisitely calibrated brass instrument, used to measure precise astronomical angles, the entire observation would be rendered valueless. Not waiting for Cook or his marine guards, Banks roused the expedition’s official astronomer, William Green, and set off immediately on foot in pursuit of the thief. In the dizzy heat, Banks followed the trail far up into the hills, accompanied only by a reluctant Green, one unarmed midshipman and a Tahitian interpreter. They penetrated seven miles inland through the Tahitian jungle, further than any European had been before: ‘The weather was excessive hot, the Thermometer before we left the tents up at 91 made our journey very tiresome. Sometimes we walk’d sometimes we ran when we imagind (which we sometimes did) that the chase was just before us till we arrivd at the top of a hill about 4 miles from the tents. From this place [the interpreter] Tubourai shew’d us a point about 3 miles off and made us understand that we were not to expect the instrument till we got there. We now considerd our situation. No arms among us but a pair of pocket pistols which I always carried; going at least 7 miles from our fort where the Indians might not be quite so submissive as at home; going also to take from them a prize for which they had ventured their lives.’

Banks decided to send back the midshipman with a brief message to Cook that armed reinforcements would be welcome. Meanwhile he and Green would press on alone, ‘telling him at the same time that it was impossible we could return till dark night’.

Before dusk, Banks ran the thief to ground in an unknown and potentially hostile village. A crowd quickly gathered round them, ‘rudely’ jostling them. Following a Tahitian custom he had already learned, Banks quickly drew out a ring on the grass, and surrounded by ‘some hundreds’ of faces, sat quietly down in the centre. Here, instead of threatening or blustering, he began to explain and negotiate. For some time nothing transpired. Then, piece by piece, starting with its heavy wooden deal case, the quadrant was solemnly returned. ‘Mr Green began to overlook the Instrument to see if any part or parts were wanting?…?The stand was not there but that we were informd had been left behind by the thief and we should have it on our return?…?Nothing else was wanting but what could easily be repaired, so we pack’d all up in grass as well as we could and proceeded homewards.’

By the time armed marines came up, sweating and jittery, about two miles down the track, Banks had completed the transaction and made several new friends. Everyone returned peacefully to Fort Venus on the shore. For this exploit, all conducted with the greatest calm and good humour, Banks earned the profound gratitude of Cook, who noted that ‘Mr Banks is always very alert upon all occasions wherein the Natives are concerned.’ Banks concluded mildly in his journal: ‘All were, you may imagine, not a little pleased at the event of our excursion.’

Excerpted from The Age of Wonder by Richard Holmes Copyright © 2009 by Richard Holmes. Excerpted by permission of Pantheon, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.