Yet another huge place, up in the group of 3 museums (Natural History, V&A, Science) in South Kensington. So we cherry-pick: machinery and marine, plus the genetics/brain development part of the Wellcome Wing.
The machinery is quite astounding: some of the earliest steam engines (beam pumps from the Cornish mines, made by Boulton, Watt and Trevithick, around 1770) are there. Extremely crude in making: hand-filed cylinders (machine tools had simply not been invented), few screws, lots of wedges to hold things together, lots of wood. Yet the progress within just a few decades was also impressive: as those machine tools started to be used widely. So much is there: Stephenson's 'Rocket' locomotive (1829, looking very fragile, small, bendy frames), Brunel's block-making machines (the first production line machinery in wide use outside textiles), early lathes, planers, steam hammers. Not that I would have liked to run any of it: dangerous looking boilers everywhere, nasty flat-belt drives.
Driven by what else? There's a full-size, working (on steam) stationary engine - the real old workhorse type that ran factories in the UK and sawmills (in NZ bush). Huge flywheel: fully 20 feet diameter, making 700hp. And so quiet! A bit of clacking from the valve gear but otherwise pure rotation without noise. This particular engine ran 1700 looms in a woollen mill well into the 1970's, and now runs for a couple of hours on Sundays (at least). I'd heard of such engines: an old bushman mentioned one with a 24ft flywheel at the 'Razorback' mill on the coast south-west of Tuatapere, but I didn't really understand just how big they were. Drive was straight from the outside of that flywheel, so it didn't need to run fast - around 40-60rpm, to make good belt speed. And very little wear at that sedate speed, hence the longevity. Quite a peak, seeing this beauty.
The genetics/brain exhibit was very current and informative. Good written material, but no book back at the store afterwards - a disappointment.