It’s some measure of the extent of urbanisation that the bookends to our day may not be birdsong but the sound of a kettle as the water in it reaches boiling point. That “tock” is made by a miniature device, a small disc consisting of alternating strips of two different metals. When exposed to heat, the metals expand at different rates, the disc gradually curves, and a switch is tripped, cutting off electricity to the kettle. Few of us know this; we write odes to nightingales, not thermostats, even though it is the latter that provides our morning soundtrack, those…