Instrument Breakage and Repair

The sextant was an essential navigational instrument, so large ships carried several as insurance against failure. As the example in Image 1 demonstrates, the telescope tube, horizon glass, and movable shades were particularly vulnerable to breakage.

When novice astronomer William Gooch joined the Vancouver Expedition in 1791, he must have cursed his luck when both his sextants were damaged beyond use only a month into his voyage. As he recorded in his journal:

“We arrived [in Rio] on the 27th Oct … I found the Micrometer screw on the Troughtons Sextant immoveable & about 10 days before I found one Corner of the Brass frame of the Dollond Sextant eaten thro with Rust & the Horizon Glass loose.”(1)

But in an extraordinary stroke of luck, Gooch soon found a man with suitable skills to repair both:

“Luckily one of Ramsdens Principal workmen was on board the Pitt as a convict he was brought on board the Daedalus & repaired both in my presence.”(1)

Remarkably, Gooch had discovered in Rio harbour a convict bound for Australia who had apprenticed under the preeminent London instrument-maker Jesse Ramsden—and the prisoner was willing to carry out the essential fixes!

Critics of the mercury barometer argued that it was easier to measure atmospheric pressure (and hence altitude) from the boiling point of water using a device like the example shown in Image 3, a hypsometer, marketed in the 19th Century as ‘Wollaston’s thermometric barometer’.

Detractors, however, condemned Wollaston’s design as “of no use; you cannot take them out of their case without breaking,”(4) and advised merely using a good thermometer in a basin of water.

British explorer Richard Francis Burton was left measuring altitude from basic “bath thermometers” after a disastrous trek across East Africa in 1857:

“All along our way we were saddened by the sight of clean-picked skeletons, and here and there the swollen corpses of porters who had perished in this place by starvation. …

'When we arrived at Rufuta I found that nearly all our instruments had been spoilt or broken, the barometer had come to grief, no aneroid had been sent from Bombay, and we had chiefly to get on with two bath thermometers.”(5)