The explorer Alexander von Humboldt is fed up, frustrated and far from home. He waits in a miserable village, by the Magdalena river in Colombia in 1801. “It was suffocatingly hot; at this time of year there is not a breath of wind. Feeling depressed, we lay on the ground in the main square,” he writes in his Personal Narrative of a Journey to the Equinoctial Regions of the New Continent.

“My barometer had broken and it was the last one I had. I had anticipated measuring the slope of the river and fixing the speed of its current and the positions of different stages through astronomical observations. Only travellers know how painful it is to suffer such accidents, which continued to dog me in the Andes and in Mexico; each time this happened I felt the same.

“Of all the instruments a traveller should carry the barometer is the one, despite all its imperfections, that caused me the most worry and whose loss I felt the most. Only chronometers, which sometimes suddenly and unpredictably change their rates, give rise to the same sense of loss.

“Indeed, after travelling thousands of leagues over land with astronomical and physical instruments, you are tempted to cry out ‘Lucky are those who travel without instruments that break, without dried plants that get wet, without animal collections that rot; lucky are those who travel the world to see it with their own eyes, trying to understand it, and recollecting the sweet emotions that nature inspires’.”