The Age of Sail in everything: Schiehallion


I was up Schiehallion on Saturday, and was reminded when I reached the car park of the part the mountain played in 18th century science. (I read quite a bit about this earlier in the year in a book which wasn’t supposed to be about the age of sail at all – it was about mountains. But it turned out to be, a bit, because everything is!)

Gravity experiment plaque

Basically, they were setting out to measure the mass of the earth, and needed something which they could compare it to – something big enough that its own mass would have a measurable effect – so a mountain – and something that stood away from other hills, and preferably was fairly symmetrical, allowing its own mass to be measured with reasonable accuracy. The comparison between the gravitational pulls of the earth and of the mountain could then be used to work out the relative mass of the earth.

It doesn’t look particularly symmetrical from this side, to be fair – although it is a big imposing lump that stands alone.

Schiehallion from the east

But as soon as you drop off the summit to the west it begins to look symmetrical again – it mostly is one long triangular ridge.

Triangular summit

A useful side effect of the experiment was the first use of contour lines to mark equal heights of land, as part of the attempt to work out the size of the hill.

This is the really classic view, from Loch Rannoch – if anyone involved with the experiment had looked at it from here, you can see why they chose it.

Triangular mountain

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