The History
Sir George Biddell Airy (27 July 1801 – 2 January 1892)
was an English mathematician and astronomer who also became the
Astronomer Royal in 1835. In 1854 Airy visited the Harton pit to
conduct an experiment into measuring the mean density of the earth
by using a pendulum and comparing information gathered at the
surface of the pit shaft with information gathered at the bottom of
the pit shaft. When the pendulum was underground it was in a room
that was vertically directly underneath the pendulum location on
the surface (image below). By using the pendulums swinging on agate
plates, timed by precision chronometers synchronized by an
electrical circuit Sir Airy found the lower pendulum was slower by
2.24 seconds per day. From samples of surface rock he estimated the
mass of the spherical shell of crust, and from this estimated that
the density of the Earth was 6.565 times that of water (or grams
per cubic centimetre). For comparison, the currently accepted value
for Earth's density is 5.5153 g/cm³.”
The Earthcache
Harton pit is now closed but at the given co-ordinates, that was
part of the Harton colliery estate, there is a pit tub and a
memorial plaque outside the entrance to the public library. To
claim this cache you need to answers the following questions and
email the answer to me via my profile:
Question One: According to the plaque how deep was the pit
shaft?
Question Two: According to the plaque how many people were employed
at Harton colliery when it closed?
To claim this cache you could also (as well as answering the
questions) take a photograph of your GPS and/or yourself with the
pit tub in the background. Please ensure the plaque is not included
in the photograph.
Please note that whilst I will look at each email received and
also look at each log and photograph to check for the right answers
etc; I may not be able to email a confirmation that all is correct.
However, incorrect answers and/or logs will be deleted without
notice. Please do not put your answer in your log entry; any logs
that contain the answers will be deleted so that following
geocachers can complete the required tasks unaided.
Thank you to the staff of Boldon Lane Library for allowing this
earthcache to be developed; and thank you to GeoawareUk for the
support and advice in the review process
Earthcache.org
Remember to look at www.earthcache.org where you can see if you
will qualify for either a bronze, silver, gold, or platinum pin
badge depending on how many earthcaches you have visited and/or
developed.