## Trigonometry lesson, 2

In the previous post on trigonometry I explained the strange chain of circumstances that led to the Latin word “sinus” (meaning a bay or inlet, or alternatively a bosom) came to be used for the ratio of the half-chord of a circular arc to the radius of the circle.

Today I was in Oxford. Despite the forecast of storms, the morning dawned cloudless and calm, and we decided to go for a walk near Dorchester-on-Thames, south-east of Oxford. The walk took us along an ancient earthwork called the Dyke Hills, across the river, up the twin hills of the Wittenham Clumps (which tower above the village of Little Wittenham), into Shillingford, across the famous bridge, and back to Dorchester on the Thames Path.

While we were climbing the hills, I remembered that Tiresias (Roger Green), in his book Notes from Overground, has this to say about Wittenham Clumps:

At 0722 BST on 7 October 1975, the Didcot side of Appleford, I caught the sun slap bang between the Tiresian mamelles of Wittenham Clumps, thus: [diagram]

Felt as thrilled as a Druid. It must be possible to see this phenomenon on most days from some vantage-point or other, but not so easy to get the train to coincide, on a clear morning, at the vital moment. Worth some research.

Curious that Paul Nash, who was obsessed with both Wittenham Clumps and the sun, and who loved juxtaposition, never (as far as I know) hit upon this symbol of male head on female bosom (let alone all the implications of another local name – Mother Dunch’s Buttocks). … Yet what does the old name Sinodun mean if not something like Breast Hill (cf. Latin sinus, French sein, and “dune”, “down”)?

So possibly the name Sinodun Hills is cognate with the word “sine”.

I am not completely confident in this identification: “dun” here is an Anglo-Saxon word meaning “hill”. Paradoxically, it gives us the word “down”. I remember that my son James once asked me (when he was at university in Sussex, under the shadow of the South Downs) why they were called Downs when they so clearly went up? The research I did suggested that the word “down” was originally “a-down”, meaning “from the Downs”. But why would an Anglo-Saxon suffix be added to a Latin (or possibly British) name?

It is true that this was an area of ancient settlement: the Dyke Hills, the Iron Age hill fort on top of one of the clumps, both show this; and the foundation of the large and influential Dorchester Abbey suggests that it was an important place (and possibly a stronghold of paganism).

Wikipedia, however, prefers an alternative derivation of the name, from the British Seno-Dunum, “Old Fort”.