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An intriguing combination of Harvey’s idea of the heart as a pump with the idea of air pressure was made in early 1700 by Stephen Hales. This English clergyman used a barometer arrangement to make a direct measurement of the blood pressure of a horse. He inserted at tube into a horse’s main artery to see how high up in the air the heart could put the blood. Unfortunately for the horse, the experiment did not work out well. She had to be sacrificed. But fortunately for other horses, the experiment only needed to be done once. But the experiment confirmed the indirect method for measuring blood pressure, which is still an important tool in medical practice today.

Excerpted from ‘Children of Promotheus: A history of Science and Technology’ by James McLachlan