‘Power dwells apart in its tranquility’1
I should have thought of it before, it’s too late now. It’s nearly ten and I didn’t remember to get a Guinness; the shops will be closed until tomorrow. In 1774 the Royal Society funded an experiment to determine the mean density of the Earth. The hope was to measure a deflection of the plumb line, caused by the gravitational attraction of a nearby mountain. If I set off now there’s a danger I won’t make it. What, amongst the mystery alcohol in the kitchen, might work for Nigella’s Guinness cake? Rum, probably, but I choose a craft larger, safer to stick with beer. Schiehallion, in Perthshire, thanks to its isolation and cone-like shape, was considered the ideal location. French astronomers, Pierre Bouguer and Charles Marie de La Condamine, following in Alexander von Humboldt’s footsteps, attempted the experiment at Chimborazo in the Viceroyalty of Peru in 1738, but downplayed their results due to the difficult conditions. I can’t remember making a cake like this before, you put the beer in a large saucepan and, over the heat, add the butter, whisking until it’s melted. I miss the meditative process of creaming butter and sugar with a wooden spoon. A Committee of Attraction was formed, members including Joseph Banks, Benjamin Franklin, Charles Mason, and Nevil Maskelyne, with the latter, once the suitable mountain had been found and granted temporary leave as Astronomer Royal, left for Perthshire. Waves of nostalgia are breaking over me, listening to The Blue Nile, while I add the cocoa and sugar to the beer—indulging myself in the synth. The expedition was well endowed, money and equipment carried over from Cook’s 1769 transit of Venus expedition. The party built two observatories on the northern and southern flanks of Schiehallion, where the zenith line was established to compare it to the hanging plumb line. ‘Beat the sour cream with the eggs and vanilla and then pour into the brown, buttery, beery pan and finally whisk in the flour and bicarb’. I can’t match Nigella’s rhythm—who can? After seventeen weeks, calculations showed a deflection such that the earth was roughly twice as dense as the quartzite mountain. In the ensuing celebrations, the northern observatory was burned to the ground. Once everything’s folded in, I pour this mixture into the tin and bake for 45(ish) minutes. The mathematician and surveyor Charles Hutton was charged with figuring an estimate for the volume of Schiehallion, from which to calculate the earth’s density. Using vertical prisms, he hit upon the idea of interpolating a series of lines at set intervals between his measured values, marking points of equal height. Contour lines have since come into common use for depicting cartographic relief. I read in the comments that ‘the cake is as rich and as deep as Irish folklore. The taste is legendary. Thank you, Ms. Lawson.’ Same, same, but different. Hutton’s measurements led him to conclude that the Earth was about
4.5g/cm34.5g/cm3
, resulting in his belief that the core of the Earth must be metal. Nigella again: ‘This cake is magnificent in its damp blackness. I can’t say that you can absolutely taste the stout in it, but there is certainly a resonant, ferrous tang which I happen to love. The best way of describing it is to say that it’s like gingerbread without the spices.’ Using this estimate for the mean density of the earth, Hutton went on to calculate the densities of the Sun, the Moon, and the planets (out to Saturn) based on their known astronomical properties, mostly to within about 20% of the modern values. I take the cake out, and let it cool for the morning.
Nigella Lawson, Chocolate Guinness Cake, accessed 11 July 2022 [https://www.nigella.com/recipes/chocolate-guinness-cake].
Information on Schiehallion from a mixture of information boards in the carpark.