Computing Earth's Mass Before G

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Computing Earth's Mass Before G

Name: Aaron
Status: student
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Question:

What were the ways of computing the mass of the earth in the 17th and 18th century?

Replies:

This link may help:

http://curious.astro.cornell.edu/question.php?number=207

Burr Zimmerman

Aaron,

The first recorded methods I know of were done in the middle of the 18th century.

One involved measuring the period of a pendulum on solid ground at sea level and on a plain very far above sea level. This can provide a ratio of the Earth's average density and the density of the ground that is above sea level.

A second involved deflection of a pendulum near a mountain. Using a star as a reference, deflection of a pendulum on top of a mountain and near the same mountain could provide a ratio of Earth mass to mountain mass.

Both are recorded in an 1893 essay by J. H. Poynting: The Mean Density of the Earth. A digitized copy of the text can be accessed currently through Google at

http://books.google.com/books?id=dg0RAAAAIAAJ&printsec=titlepage &source=gbs_v2_summary_r&cad=0#v=onepage&q=&f=false

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

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Update: June 2012