Henry Cavendish

Investigator of Hydrogen; Calculator of Earth’s Gravitational Constant

Cavendish was born on October 10, 1731, to a wealthy English family in Nice, France. He was sent to Dr. Newcome’s Academy in London and entered Cambridge University in 1749. Cavendish left the school four years later without a degree, an occurrence that was not uncommon in his day. His father provided him with a laboratory and generous allowance. Cavendish became a member of the Royal Society in 1760 and attended the meetings regularly. While at Society meetings, he rarely spoke but listened avidly to the debates. His shy demeanor developed into increasingly reclusive behavior as he grew older.

Many of Cavendish’s significant discoveries were in chemistry. One major finding was that the composition of the atmosphere remained constant regardless of location. He also experimented with atmospheric gases and studied what he called inflammable air. This gas was later named hydrogen by ANTOINE LAVOISIER. In a 1766 paper he discussed many of hydrogen’s properties, noting that it was much lighter than other gases. He experimented with hydrogen during 1784 and combined it with ordinary air. When the hydrogen burned, water was produced. This conclusively demonstrated that water was not an element as previously believed, but rather a compound. Cavendish isolated another gas, nitrogen, but did not publish his results and therefore was not credited with its discovery. Cavendish used nitrogen to create nitric acid in 1795.

Although he experimented extensively with electricity and wrote personal notes on its properties and uses during the 1770s, he only published a few of his findings.

His last major work was a calculation of Earth’s gravitational force. ISAAC NEWTON had postulated a way to find this constant value but could not do the exacting experimentation. Cavendish devised a system of lightweight balls suspended on a flexible rod. The gravitational attraction between the objects caused the rod to twist. Using this minute measurement of attraction and knowing the mass of the objects, Cavendish was able to find the gravitational force between the two objects. From that information he was able to calculate the gravitational force for Earth. He used this value to eventually find the density and mass of Earth within 10% of current estimates. In 1798, Cavendish published his findings.

In his later years Cavendish became increasingly withdrawn. He shunned the company of others, particularly women. He died at his London home on February 24, in 1810.

Henry Cavendish’s Legacy

Much of what Cavendish discovered during his solitary life was not shared with the scientific community for many years. What he did share prodded important information for understanding gravity and how gases interact.

The isolation and study of hydrogen provided scientists with an understanding of a known gas that could be used for comparison with other gases. Cavendish discovered that hydrogen was the lightest known gas, and, as such, it became the basis for chemist JOHN DALTON’s comparative atomic weights, which in turn were the precursor to the periodic table. As the lowest density gas, hydrogen was useful for a number of things. Its lighter­ than­ air properties made it very useful in the construction of dirigibles. These flying airships became multipurpose modes of transportation. The use of hydrogen in water experiments allowed Cavendish to show that water was not an element and paved the way to understanding the difference between elements and compounds. This break from the Greek idea about the four components of matter (fire, earth, air, and water) opened new paths of thinking among scientists.

The calculation of the constant gravitational force on Earth not only allowed Cavendish to estimate the mass of Earth, it also prodded the key to understanding other gravitational systems. This constant has been used to explain tides, the orbits of the moon and planets, and the paths of falling objects. It is a factor in projectile motion. Satellites used for communications and our understanding of planetary systems are dependent upon this constant.

Perhaps the greatest contribution of Cavendish came after his death. In 1871 his family funded the creation of a laboratory at Cambridge in his honor. The prestigious Cavendish Laboratory is well known for its experimental physics research facilities.

While Cavendish did not share many of his findings, JAMES MAXWELL collected and published Cavendish’s notebooks in 1879, nearly seven decades after his death. In these writings Cavendish described many of the principles of electricity that are credited to later scientists, for example, the concept of voltage and the inverse square law of attraction. Historians have speculated that Cavendish’s work, had it been disseminated during his life, could have precipitated some of the great leaps in scientific thought that occurred many years later.

Henry Cavendish – 1731-­1810