I’m supposed to be preparing a lecture on the eighteenth-century pneumatic chemists and I noticed this morning that today is the birthday of Stephen Hales who was responsible for a small invention that made pneumatic chemistry possible, so I decided to write a post about him.
Hales, who is largely unknown today, except by experts, was regarded in the eighteenth century as one of the most important English natural historians with an international reputation amongst both natural historians and chemists. Born on the 17th September 1677 the tenth child and sixth son of Thomas Hales, heir to the Baronetcy of Beakesbourne and Brymore. As a younger son he was destined for the clergy and duly ordained in 1703 after graduating BA in 1700 at Corpus Christi College Cambridge. He obtained a fellowship in the same year and qualified MA in 1704. He remained in Cambridge until 1708 devoting his time to the study of the sciences mostly in tandem with William Stukeley, who would later become Newton’s physician. The two of them, being Cambridge men, studied Newton’s physics and astronomy as well as John Ray’s natural history.
Family connections found a curacy for Hales, which was the start of his long and successful church career, the high point of which was being appointed private chaplain to Princess Augusta, Dowager Princess of Wales and mother of George III in 1751. He was awarded a Doctor of Divinity by the University of Oxford in 1733 and is said to have turned down the offer of a canonry at Windsor from George II. Princess Augusta held him in such esteem that she had a monument erected to his memory in Westminster Abbey after his death in 1761, at the ripe old age of 83.
However as stated above Hales was not only a successful pastor but also a very successful and important amateur natural historian making him an excellent example of the eighteenth- and nineteenth-century Anglican clergymen who devoted themselves to the study of the sciences making substantial advances to many fields. This historical phenomenon, of course, makes a mockery of the claims of the Gnu Atheists that religion and science are incompatible and that belief in God somehow hinders scientific thought.
Hales who became a member of the Royal Society in 1718 devoted his scientific studies to the circulatory systems of plants and animals. The results of his experimental studies on plants where published in his Vegetable Staticks. Hales determined the direction and force of sap flow in plants by inserting glass tubes into the stump of a vine with the branches cut off. He also inserted glass tubes containing water into the root systems of plants to determine the water absorption rate. Hales’ greatest achievement in his plant studies was to measure the transpiration rate. Through a series of complex and ingenious experiments he was able to determine how much water a plant perspired during its growing season and to demonstrate that this transpiration helped to draw water up through the roots.
Hales carries out similar experiments over many years on the circulatory systems of animals, which he published in his Haemastaticks in 1733. He later published both books together as his Statical Essays. Using the same method of inserting glass tubes into arteries and veins of various animals, Hales made the first ever blood pressure measurements. He then went on to measure cardiac output and compare pulse rates and blood pressure. These experiments were conducted on live animals without the benefits of sedation, which led his friend and neighbour, Alexander Pope, a dog lover, to condemn him for his cruelty to animals.
During his plant experiments Hales noted that air was expelled by his plants along with the water and he set out to devise methods to collect and measure the quantities of air thus produced. This is where Hales becomes interesting for the pneumatic chemists, who succeeded him in the eighteenth century and thus for my planned lecture. Hales devised a series of apparatuses to collect the air, which culminated in his invention of the pneumatic trough. A device that could be set to the general purpose of collecting gases separated from the generating apparatus.
The pneumatic trough would go on to be further developed by Henry Cavendish, William Brownrigg, Joseph Priestly and Antoine Lavoisier all of whom would use it in the discovery of various gasses, most notably hydrogen and oxygen; discoveries that would lead to the discovery of the composition of water and the beginnings of modern molecular chemistry. All of these researchers acknowledged their debt to Hales and his invention.
Throughout the late eighteenth century and the nineteenth century all of the great natural historians who laid the foundations of modern biology also acknowledge their debt to Hales for his pioneering work in both animal and plant physiology. It is only in the late nineteenth century that he began to be forgotten and to slide into obscurity; to become only the subject of study of specialist historians of science and no longer to be counted amongst the great natural historians.
As we have seen Hales was not just a brilliant theorist but also a very practical investigator designing and building complex experimental apparatus with which to conduct his researches. He applied this practical bent to the solution of an important social problem. His researches into air were a continuation of work begun in the seventeenth century by people such as Boyle and Hooke into air and its properties. One of the central concerns of these researches was the investigation of bad or foul airs, like those found in swamps, mines and enclosed spaces, such as prisons or ships. In fact Brownrigg’s development of Hales’ pneumatic trough was dedicated to this research. Hales was one of several researchers to invent a ventilator driven by bellows worked by hand and in larger versions by windmills to provide fresh air to enclosed spaces. Hales’ ventilators were a success and were widely employed in ships, prisons and mines.
Addendum: 17 September 2020
I think it’s an important part of Hales’ legacy that his celebrated ventilators were trialled by his contacts among slaveship owners, and that ventilation was advanced by supporters of slavery as a meliorist response to the conditions on board slaveships.
Hales is a classic example of those small scientific researchers, who upon investigation turn out not to be so small after all, who get lost and forgotten in our hagiographical presentation of the so-called giants of science. Next time you are at your doctors having your blood pressure checked spare a thought for the Reverend Stephen Hales the very first person to measure blood pressure.