A kettle never takes the water’s temperature. Near the handle, at the bottom of a short tube that opens into the top of the jug, sits a small dished disc of two metals bonded together. While the water is merely hot, nothing reaches it. Once the water really boils, steam is pushed down the tube, warms the disc, and the disc snaps inside out with the click that opens the circuit. That is why a kettle still works on a mountain, where water boils below a hundred degrees: it was never waiting for a number, only for the water to start sending something up. It is a patient arrangement. The kettle doesn’t go and check. It waits to be told, by the one thing that can only arrive once the job is done.