Henry Cavendish (1731 – 1810) The Weighing of the Earth

Henry Cavendish (1731 – 1810)

• The Weighing of the Earth

Personal Life

• As the grandson of the Second Duke of Devonshire, he was considered nobility
• He attended Cambridge University from 1749 – 1753, but left without earning a degree
• His inherited fortune enabled him to pursue scientific studies
• Viewed as solitary and eccentric, he had no friends apart from his family
• Asperger’s Syndrome – account for his unusual shyness
• Prohibited from publishing his work until James Clerk Maxwell looked through his papers
• Saw credit to most his discoveries had been given to others:
• Richter’s Law of Reciprocal Proportions, Ohm’s Law, Dalton’s Law of Partial Pressures

Discovery of Hydrogen

• In 1766, In a paper called On Factitious Airs Cavendish addresses a “inflammable air” which forms water as a result of combustion.
• Antoine Lavoisier later reproduced the experiment giving Cavendish’s element the name Hydrogen

Composition of Atmosphere

• Established an accurate composition of the atmosphere
• ~79% “phlogisticated” air (nitrogen and argon)
• ~21% “dephlogisticated” air (oxygen)

Weighing of Earth

• Cavendish used an torsion balance apparatus to complete the experiment in 1797
• Originally created by John Mitchell who died before he could put it to use
• Apparatus sent in crates to Cavendish
• The apparatus consisted of a torsion balance to measure the gravitational attraction between two 350 pound lead spheres
• Consisted of a 6-ft wooden rod with metal spheres attached to each end, hanging from a wire which twisted as a result of the gravitation attraction between them
• Wind proof room
• Torsion of wire measure by the telescope

Gravitation Constant and Mass of Earth

• With G, he could easily calculate the earth’s mass to be 5.9725 billion trillion tons (his estimate was 1% off)