Stephen Hales was a clergyman, naturalist and inventor active in the early eighteenth century. Hales was interested in pneumatics and spent much time studying the chemistry of the air, the movement of water in plants, breathing and blood circulation. He was the first scientist to measure blood pressure.

Statical Essays contains a collection of Hales’s writings on these subjects. This first volume concerns his botanical research. In plants, he looked at how water travelled from their roots to their leaves. He also speculated that they used light as a source of energy for growth (photosynthesis) as well as absorbing air through the leaves. Although little understood in his own time and his studies quickly forgotten, several of his theories on the subject have since been proven correct.