 We should assume, Hartley writes, that the body’s “component particles” are “subjected to the same subtle laws” (OM 1, prop. 9) as are all other material entities. The subtle laws are those Newton suggested in the “Queries” to his Opticks, and which Stephen Hales (1677–1761, remembered today as the father of plant physiology and for the measurement of blood pressure) further developed in the chemical theory in his Statical Essays—i.e., Vegetable Staticks (1727) and Haemastaticks (1733). Descartes had earlier proposed a model of neural physiology, but in 1740s Britain the physics the model depended upon would have looked out of date. Hartley, in contrast, presented a “theory of vibrations” that explained how the “component particles” that constitute the nerves and brain interact with the physical universe suggested by Newton—a world composed of “forces of attraction and repulsion” and having a minimum of solid matter.