 (1) We noted above Hartley’s collaboration with his friend Stephen Hales to discover a medical treatment that would dissolve bladder stones. Following Newton, Hales believed “forces of attraction and repulsion” to be the basis of physical nature, and through various chemical experiments he demonstrated that solid concretions, including bladder stones, were compounds that had locked within themselves large quantities of “air,” which normally manifests a strongly repelling force. The “air” within a bladder stone could be released, and the stone dissolved, through reaction with an agent that would change the pH of the urine. Such chemicals are plentiful in the laboratory; the two men were looking for one that a person could safely ingest.