Maskelyne at Schiehallion

[Martin Meredith]

It isn't often that my twin obsessions of Munro-bagging and astronomy collide, but they did yesterday at the base of Schiehallion, a 3553 ft Scottish mountain lying to the east of Rannoch Moor. Here I came across the following plaque to the work of Nevil Maskelyne, the Astronomer Royal, who used Newton's theory of gravity to estimate the density of the Earth. He did this by measuring the deflection of a plumb-line caused by the attractive force of Schiehallion. The deflection in turn was estimated by examining the distance of 77 stars from zenith on either side of the mountain, using the same zenith instrument used by Maskelyne during the 1761 transit of Venus.

The entire method and the accuracy of the outcome is well-described in this commemorative article.

Schiehallion is in some ways an exceptional mountain, standing some distance away from other mountain ranges (cleaner data), being steep on two sides (allowing the instrument to get close to the centre of mass on each side), and being almost symmetrical (easier to estimate its mass). As part of the need to precisely survey the mountain during the experiment, Charles Hutton was the first to use contour lines. On learning this I was rather hoping Charles Hutton was related to the father of geology, the Scot James Hutton, but although they were born within 10 years of each other I don't see any relationship.

Here's an earlier shot of Schiehallion from a neighbouring mountain range to the west:

In hillwalking terms it is a mountain of two parts, an easy well-made path up the first half through bracken and heather, followed suddenly on achieving the ridge by an extremely rocky landscape calling for stout boots, ending in a surprisingly bijou summit. If you do toil against gravity to reach the top, I can recommend rewarding yourself with a nice pint of Schiehallion IPA in a bar of the same name in the Macdonald Hotel in nearby Kinloch Rannoch!

Martin

 

[andrew s]

1 hour ago, Martin Meredith said:

Munro-bagging

You must have a very big bag.

Regards Andrew

PS Nice shots. You deserve the IPA

[Knight of Clear Skies]

I vaguely recognised the names in the thread title but was still expecting to see an astronomical image when I clicked on it. If Andromeda gave us Var 1, the star that expanded the universe, can Scotland lay claim to the mountain that gave us G?

[Les Ewan]

I came across the plaque when I climbed Schiehallion in 2004 the weather was hot with good visibility with Ben Nevis in one direction and Arthurs Seat and ther Pentland Hills  on the other on view  on the summit .Its a great mountain to climb made more interesting with its scientific past.

[DRT]

On 01/08/2017 at 12:52, Martin Meredith said:

a surprisingly bijou summit

This is that summit on a frosty morning in November 2010...

Whilst sitting eating my breakfast on the summit that morning I saw one of these for the first time...

The circular rainbow-like hallo appeared to be floating about 10m out from the pointed rock and was created/projected through ice crystals on the top of that rock. It looked much clearer on the day than it does in the picture and was about the size of a basketball. 

I knew the general story of Schiehallion being used in that experiment but didn't know the detail. Thanks for posting!