Dobson's original ozone spectrometer, 1926.
© Science Museum / Science & Society Picture Library
This instrument was designed by Gordon Dobson of Oxford University to measure the amount of ozone in the stratosphere. He set it up on the ground, pointing vertically, to record the amount of ultra-violet light that had penetrated the atmosphere. This technique was key to the detection of the hole in the ozone layer over the Antarctic in 1985.