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)