John Hadley

Biography

John Hadley (1731-1764) was an English chemist and physician who made significant contributions to early experimental chemistry during the mid-18th century. Born in London to Henry Hadley, he received his education at Queens' College, Cambridge, where he graduated with a Bachelor of Arts degree in 1753. His academic excellence and scientific aptitude led to his appointment in 1756 as the fourth Professor of Chemistry at Cambridge University, a position that holds the distinction of being the oldest continuously occupied chair of Chemistry in the United Kingdom.

During his tenure at Cambridge, Hadley conducted groundbreaking research in collaboration with the renowned American polymath Benjamin Franklin. In 1758, they performed a series of experiments investigating the phenomenon of latent heat, particularly focusing on evaporation and cooling effects. Their most notable experiment involved spraying a mercury thermometer with ether and then evaporating it by blowing air across the surface. This procedure resulted in the thermometer registering temperatures as low as minus seven degrees Celsius, even when conducted in a warm room. This work contributed to the early understanding of evaporation cooling and heat transfer principles.

Since the Chemistry Professorship at Cambridge was unpaid, Hadley pursued medical studies to secure financial stability. In 1758, he obtained a Physick Fellowship, which enabled him to practice medicine alongside his chemical research. Two years later, in 1760, he relocated to London to take up a position as Assistant Physician at St Thomas' Hospital, one of London's most prestigious medical institutions. His medical career progressed rapidly, and by 1763, he had been promoted to full Physician at Charterhouse School, while also achieving Fellowship of the Royal College of Physicians.

Hadley's scientific contributions were recognized by his election as a Fellow of the Royal Society in 1758, an honor that acknowledged his research achievements and standing within the scientific community. On December 16, 1763, he performed what is recorded as the first dissection of a mummy in British history, demonstrating his interest in advancing medical knowledge through anatomical investigation. Unfortunately, his promising career was cut short when he died of fever in 1764 at the young age of 33, leaving behind a legacy of important early work in experimental chemistry and medicine.