Before Stephen Hales, plants were described.

Their appearance was catalogued. Their uses were recorded. Their parts were named. The great botanists of the preceding centuries had built an extraordinary descriptive record of the plant kingdom.

But how plants worked — what moved inside them, what forces drove their growth, how water traveled from root to leaf — was a matter of theory and analogy, not measurement.

Hales changed that.

Who He Was

Stephen Hales was an English clergyman — the vicar of Teddington, a village outside London. He was also a natural philosopher with a systematic mind and a willingness to conduct experiments that required extraordinary patience.

In 1727 he published Vegetable Staticks — a record of quantitative experiments on plant physiology that had no precedent in the literature.

He was fifty-three years old when it appeared.

He had spent decades taking measurements.

What He Measured...