Gaining a new insight, perhaps, from Celia Fiennes's 1690s travel accounts into the economics of the Cornish tin and copper mines in the years just before Newcomen invented his engine.

A few stray observations:

She notes the tin mines, mainly near the southern coast, had major problems with mine flooding. If they could afford it, they used horse-driven pumps, better still they'd use water-powered ones like those used for London or Derby's domestic water supply - but capital costs high.

She was presumably told, while there that the water-powered mills "do five times more good" than the horse-driven ones. Would be interesting to corroborate this productivity improvement using other sources.

Also, that's a pretty huge improvement! Why bother with steam?

So here's the other thing: the fuel sources don't make sense to me from a "costs drove the invention of steam engines" perspective.

1) She notes that the mines near the north coast of Cornwall predominantly dig for copper, and that flooding not as big an issue.

But 2) the northern-coast copper mines were the ones that actually got cheap coal. She notes that due to on-and-off war, as well as privateers and pirates in the Channel, coal-laden boats from the Bristol coalfields mainly served the north, and wouldn't risk going to the south.

Perhaps this changed by the 1710s? I suppose a lot can change in a decade, but if anything the wars with France intensified immediately after she wrote, due to the Wars of the Spanish Succession.

And then there's 3) the matter of the demand for coal in Cornwall:

Fiennes notes that in the tin-mining south, where coal supply is lacking and thus more expensive, and where mine flooding more of an issue, they were actually doing the tin-smelting themselves. Predominantly by burning turf. Other main fuel for the area being furze/gorse.

Whereas in the north, where coal was cheaper due to the Bristol supply, and where mine flooding less of an issue, the copper they mined was instead being sent off to Bristol for smelting (exception being a small bit of smelting at St Ives).

Finally, 4) Fiennes makes a very interesting observation about the capital costs of the mills, either horse-drawn or water-driven, and presumably relevant to any early steam engines for pumping too: in Cornwall, the main constraint is the county's lack of *timber*.

So a purely economic story, unless something dramatically changed between 1698 and the 1710s, doesn't add up for me:

Cornwall seems to have actually had high capital costs, and places that most needed to deal with flooding, in the south, also lacked access to the coal supply.

It's a bit strange, too, that the tin-smelting south would do its own smelting given the higher fuel cost. But I suspect tin-smelting requires less heat?

A stray observation: she didn't see a single windmill there. Why didn't they tap this whole other energy source for pumping?!

I've got a bunch of extremely specific and detailed papers sitting in my inbox, sent to me by a specialist that I still need to read in detail, and which may have some answers or even corrections to the Fiennes observations.

All the same, thought I'd think aloud on this!

A bit more. I'll add to this if more comes up, as this is an off-the-cuff thread: furze as a fuel clearly couldn't get to very high temperatures, as she notes that her landlady in the south could only boil food, rather than roast it - again, the constraint being lack of wood fuel

She expresses surprise that wood couldn't just be imported by ship, which is where she hears again that due to French war/privateering, it's risky and thus costly for ships laden with wood to get round Land's End and supply the south coast.

An absolutely crucial piece of the story will be details of Newcomen's early experiments. We know the later *successful* ones were at coal mines, as the fuel was essentially free. But if coal was v expensive for first ones it may fundamentally undermine Robert Allen's case study.

It would leave intact Allen's thesis with regards to where the steam engine was profitable to be *applied*. But it would undermine his claim that factor prices were a source of the *invention* and even the initial tinkering with Newcomen's engine.