Schiehallion
I ascended Schiehallion in the summer this year. That famous high
mountain is in the dead centre of Scotland in Perthshire. It was at the
heart of a scientific experiment in the eighteenth century. I want to
tell you about the experiment.
The Astronomer Royal, Nevil Maskelyne, spent seventeen weeks living in
a bothy on the mountain. He was there to measure the mass of the world.
It wasn’t known at that time if the Earth was hollow in the middle or
full of something.
Maskelyne was wanting to find a mountain whose volume was easy enough
to measure. He was going to measure what fraction of the earth the
mountain was representing. He would then measure the weight of the
mountain according to its gravitational pull. From that, he would get
the weight of the entire Earth.
The first thing was to find a suitable mountain. The Royal Society sent
Charles Mason to the Highlands of Scotland. He found Schiehallion.
It wasn’t easy for Nevil Maskelyne to get there. The roads were poor
and there were no railway lines. Maskelyne travelled by sea to Perth.
He reached the mountain on the last day of June 1774. He gave work to
the local people. They built two experimental stations on the mountain.
He used the stars to measure the true vertical. He used pendulums and
he measured the sideways gravitational pull of the mountain. From that,
he obtained the density of the mountain. Then he measured the volume of
the mountain to get its weight.
He obtained assistance in that from the mathematician, Charles Hutton.
Hutton decided that the best way to measure the volume of Schiehallion was
to divide the mountain into horizontal slices. For that, he created lines
of equal altitude, contour lines. That was the first time that people [had]
used contour lines to map a mountain. Where would our maps be without such
things today?!
Sìth Chailleann (1)
Dhìrich mi Sìth Chailleann as t-samhradh am-bliadhna. Tha a’ bheinn àrd
ainmeil sin ann an teis-meadhan na h-Alba ann an Siorrachd Pheairt. Bha i
aig cridhe deuchainn saidheansail anns an ochdamh linn deug. Tha mi airson
innse dhuibh mu dheidhinn na deuchainne.
Chuir an Reultair Rìoghail, Nevil Maskelyne, seachad seachd seachdainean
deug a’ fuireach ann am bothan air a’ bheinn. Bha e ann airson cuideam an
t-saoghail a thomhas. Cha robh fios aig an àm sin an robh an Talamh falamh
sa mheadhan no làn rudeigin.
Bha Maskelyne ag iarraidh beinn a lorg a bha furasta gu leòr a thomhas a
thaobh a meud-lìonaidh. Bha e a’ dol a thomhas dè a’ bhloigh dhen t-saoghal
a bha a’ bheinn a’ riochdachadh. Bhiodh e an uair sin a’ tomhas cuideam na
beinne a rèir a h-iom-tharraing, no gravity. Às a sin, gheibheadh
e cuideam na cruinne gu lèir.
B’ e a’ chiad rud beinn fhreagarrach a lorg. Chuir an Comann Rìoghail fear
Teàrlach Mason gu ruige Gàidhealtachd na h-Alba. Lorg e Sìth Chailleann.
Cha robh e furasta do Nevil Maskelyne faighinn ann. Bha na rathaidean
truagh agus cha robh rathaidean-iarainn ann. Chaidh Maskelyne ann air
soitheach-mara gu ruige Peairt. Ràinig e a’ bheinn air an latha mu
dheireadh dhen Ògmhios, seachd ceud deug, seachdad ʼs a ceithir (1774).
Thug e obair do mhuinntir an àite. Thog iad dà ionad-deuchainne air a’
bheinn.
Chleachd e na rionnagan airson a bhith a’ tomhas fìor-dhìreachdas no ‘ true vertical’. Chuir e crochadain an sàs agus rinn e tomhas air
tarraing na beinne orra don taobh. Às a sin, fhuair e dùmhlachd na beinne.
An uair sin thomhais e meud-lìonaidh na beinne airson a cuideam fhaighinn.
Fhuair e taic ann an sin bho fhear-matamataig, Teàrlach Hutton. Chuir
Hutton roimhe gur e an dòigh as fheàrr airson tomhas-lìonaidh a dhèanamh
air Sìth Chailleann a bhith a’ roinneadh na beinne ann an sliseagan
còmhnard. Airson sin, chruthaich e loidhnichean co-àirde nocontour lines
. B’ e sin a’ chiad turas a chleachd daoine loidhnichean co-àirde airson
mapa a dhèanamh de bheinn. Càite am biodh ar mapaichean às aonais na
leithid an-diugh?!
