Henry Cavendish | Biography

Today Henry Cavendish is recognized as one of the most brilliant scientists of his day, but his contemporaries knew him to be an extremely unusual person. Throughout his life Cavendish avoided women entirely; he even went so far as to order his female servants to stay out of his way, or they would be fired. He was so shy he almost never left his house, except to attend the weekly dinners and meetings of the scientific Royal Society. Sometimes, he would hang around outside the meeting room, waiting to slip in when no one would notice him. If a stranger came near him, he quickly walked away. The only picture we now have of Cavendish is a watercolor sketch that was painted without his knowledge. He never changed his style of dress; he wore old-fashioned clothes, which he replaced with an identical outfit according to a regular schedule.

Whatever he lacked in social graces, Cavendish, a Cambridge scholar, made up for in scientific excellence. His laboratories and experiments were all that he cared about, and he managed to take part in the scientific activities of his day even though he preferred to work alone. After leaving Cambridge without getting a degree, which was not unusual then, Cavendish moved in with his father in London, England, where he set up a laboratory and workshop. Cavendish also maintained a large library in a separate building in London, and he had a country house equipped with another laboratory.

In 1766 Cavendish presented a paper to the Royal Society telling how he discovered hydrogen gas, which he called inflammable air. Cavendish produced hydrogen by combining metals with acids. For example, he found that hydrogen is produced when zinc, iron, or tin is dropped into hydrochloric acid or a diluted sulfuric acid. Cavendish's inflammable air was given its modern name of hydrogen in 1791 by Antoine-Laurent Lavoisier. Although a few chemists had collected hydrogen previously, Cavendish was the first to distinguish it from ordinary air and to investigate its specific properties. He found that hydrogen was extremely light in comparison to other gases. Eventually, this discovery was used to develop hydrogen-filled balloons, which could travel higher and farther than balloons filled with hot air. In some of his most important experiments, done during 1784 and 1785, Cavendish discovered that when hydrogen is combined with air, the mixture explodes and creates water. Cavendish even figured out approximately how much hydrogen and air combine to produce water, which anticipated the development of water 's modern chemical formula (H₂O). At that time, many people still believed that water itself was a basic chemical element, along with fire, air, and earth.

Cavendish also discovered the inert gas argon while experimenting with nitrogen. Cavendish isolated nitrogen, although he is not credited with its discovery because his work remained unpublished, and then combined it electrically with oxygen. When finishing the experiment, he found that about one percent of the original gas was unaccounted for in the reaction. In 1894 this mysterious gas was identified as argon by Sir William Ramsey. Cavendish also discovered the composition of nitric acid. By dissolving the nitrogen-oxygen gas in water, he created nitric acid, proving that it is composed of nitrogen, oxygen, and hydrogen.

In a series of about 400 experiments, Cavendish established that the composition of air is the same regardless of the air's geographic origin. He determined that air contains about twenty-one percent oxygen, and he studied the properties of carbon dioxide, comparing its specific properties with those of air. During the same period Cavendish studied the freezing points of mercury and various acids.

Cavendish also performed many important physical and electrical experiments. He was the first scientist to calculate the Earth 's mass--and he was right, to within about ten percent of the best modern estimates. In this spectacular experiment, Cavendish made the most important advance in the understanding of gravity since Isaac Newton proposed the law of gravity in 1665. Newton's law lacked one key ingredient--a number called the gravitational constant, which represents gravity's force of attraction between objects. Without this number scientists could not calculate gravity 's effect on the orbits of the moon and planets, the ebb and flow of the ocean's tides, or the path of falling objects and projectiles. Cavendish measured gravity's force of attraction, using a method suggested earlier by John Michell (1724-1793). The gravitational attraction between objects that are small enough to work with in the lab is very weak, so Cavendish's equipment had to be very sensitive to detect the force. His equipment consisted of a lightweight rod suspended by a wire; small balls were placed at both ends of the rod. When Cavendish placed larger balls near the small ones, the gravitational attraction between each pair of balls caused the rod to twist. From this he calculated the strength of attraction, which enabled him to solve Newton's equation for the gravitational constant. Once that number was known, Cavendish was then able to calculate the mass of the Earth as well as its average density. Cavendish had made the law of gravity complete for the first time.

In Cavendish's day, electrical experimentation had become quite fashionable in scientific and popular circles throughout England and continental Europe. Cavendish anticipated many basic concepts that were later developed by Michael Faraday, Charles-Augustin Coulomb, and others. He explained how charged objects attract or repel each other, and he introduced the idea of voltage, or electrical potential. He also showed that different materials conduct different amounts of electric current and studied the capacity of those materials to store an electrical charge.

Although Cavendish published two papers on electricity during the 1770s, his work remained unknown until his notebooks and manuscripts were discovered and published by James Clerk Maxwell in 1879. Much of Cavendish's other scientific research in optics, geology, magnetism, and pure mathematics was not revealed during his lifetime, but Cavendish did not care whether his research was appreciated or whether he got credit for his work. He studied science to satisfy his own curiosity. When Cavendish died, his relatives left much of his fortune to Cambridge University, which established its Cavendish Professorship and the world-renowned Cavendish Laboratory.